Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session T1: Poster Session III (13:00 - 16:00)Poster
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Room: Exhibit Hall J |
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T1.00001: ATOMIC, MOLECULAR AND OPTICAL (AMO) PHYSICS |
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T1.00002: Nonlinear Mixing of Optical Vortices with Fractional Topological Charges in Raman Sideband Generation. James Strohaber, Yakup Boran, Muhammed Sayrac, Lewis Johnson, Feng Zhu, Alexandre Kolomenskii, Hans Schuessler We studied the nonlinear parametric interaction of femtosecond fractionally-charged optical vortices in a Raman-active medium. Propagation of such beams is described using the Kirchhoff-Fresnel integrals by embedding a non-integer 2pi phase step in a Gaussian beam profile. When using fractionally-charged pump or Stokes beams, we observed the production of new topological charge and phase discontinuities in the Raman field. These newly generated fractionally-charged Raman vortex beams were found to follow the same orbital angular momentum algebra derived by [Strohaber et al., Opt. Lett. 37, 3411 (2012)] for integer vortex beams. [Preview Abstract] |
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T1.00003: Toward Imaging of Small Objects with XUV Radiation Muhammed Sayrac, Alexandre A. Kolomenski, Yakup Boran, Hans Schuessler The coherent diffraction imaging (CDI) technique has the potential to capture high resolution images of nano- or micron-sized structures when using XUV radiation obtained by high harmonic radiation (HHG) process. When a small object is exposed to XUV radiation, a diffraction pattern of the object is created. The advances in the coherent HHG enable obtaining photon flux sufficient for XUV imaging [1]. The diffractive imaging technique from coherent table top XUV beams have made possible nanometer-scale resolution imaging by replacing the imaging optics with a computer reconstruction algorithm [2]. In this study, we present our initial work on diffractive imaging using a tabletop XUV source. The initial investigation of imaging of a micron-sized mesh with an optimized HHG source [3] is demonstrated. This work was supported in part by the Robert A. Welch Foundation Grant No. A1546 and the Qatar Foundation under the grant NPRP 8-735-1-154. M. Sayrac acknowledges support from the Ministry of National Education of the Republic of Turkey. [1] G. Vaschenko, et al. Optics Letters 31 (2006). [2] C. Song, et al. Physical Review B 75 (2007). [3] M. Sayrac, et al. Rev. Sci. Instrum. 86 (2015). [Preview Abstract] |
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T1.00004: Propagation of Quantized Optical Field in Gaussian Spatial Modes through non-linear Medium Zhihao Xiao, R. Nicholas Lanning, Mi Zhang, Irina Novikova, Eugeniy Mikhailov, Jonathan Dowling We examine the propagation of quantized optical field, in Gaussian spatial modes, through a non-linear medium. Due to the structure of Gaussian spatial modes, and non-linearity of the medium, both classical amplitude and the quantum state of the optical field will propagate in a unique way. We simulate the injection a linearly polarized laser beam into a Rb vapor cell, which acts as non-linear medium, creating squeezed vacuum state of light which is linearly polarized in the perpendicular direction. We examine the model using semi-classical calculation and then fully quantize the optical field. The Rb atomic structure is simplified as a three-level system. We further examine the mechanism of generation of squeezed state of light in this process and compare the theory with our experiment. Finally we discuss the distribution of squeezed state among different Gaussian spatial modes and possible improvement in setup to achieve the desired squeezed state. [Preview Abstract] |
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T1.00005: Focusing properties of vector optical fields with both orientation and ellipticity arbitrarily modulated Guigeng Liu, Xuemei Wu, Juan Liang, Xi Cheng, Yupei Wang, Chenghou Tu Arbitrary modulation of both the orientation and the ellipticity is realized through a spatial light modulator and a common path interferometer. Compared with linearly and hybrid vector optical fields, those fields process an extra degree of freedom to modulate. Through simulation, we analyze the focusing properties of those fields when both the orientation and the ellipticity are modulated. By modulating the ellipticity of radially polarized light, one can adjust the relative energy between the transverse and the longitudinal components arbitrarily, which can also be understood that the total fields are the combination of radially and azimuthally polarized light. And also, the polarization distribution of focusing fields resembles the polarization of the input fields. When ellipticity of input fields varies azimuthally, the energy distribution of focusing fields also depends on the input fields. We let the orientation of input fields keep azimuthal, but left-circularly polarized in the first and the third quadrant, right-circularly polarized in the second and the fourth quadrant, thus we get square patterned focusing fields. Those novel focusing fields can be helpful in optical trapping and optical micromachining. [Preview Abstract] |
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T1.00006: Optical-reciprocity-induced symmetry in photonic heterostructures and its manifestation in scattering PT-symmetry breaking Li Ge, Liang Feng The scattering matrix $S$ obeys the symmetry property ${\cal PT}S{\cal PT}=S^{-1}$ in a Parity-Time (${\cal PT}$) symmetric system and the unitary relation $S^\dagger S=1$ in the absence of gain and loss. Here we report a different symmetry relation of $S$ in a one-dimensional heterostructure, which is given by the amplitude ratio of the incident waves in the scattering eigenstates. It originates from the optical reciprocity and holds independent of the presence of gain and loss in the system. Guided by this symmetry relation, we probe the reminiscence of the spontaneous symmetry breaking of a $\cal PT$-symmetric $S$ matrix, when the system does not have exact $\cal PT$ symmetry due to unbalanced gain and loss and even in the absence of gain. We show that the additional symmetry relation provides a clear evidence of a quasi-transition, even when all previously found signatures of the $\cal PT$ symmetry breaking of $S$ are completely erased. [Preview Abstract] |
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T1.00007: Ultrastrong coupling phenomena beyond the Dicke model Tuomas Jaako, Ze-Liang Xiang, Juan Jose Garcia-Ripoll, Peter Rabl We study effective light-matter interactions in a circuit QED system consisting of a single $LC$ resonator, which is coupled symmetrically to multiple superconducting qubits. Starting from a minimal circuit model, we demonstrate that in addition to the usual collective qubit-photon coupling the resulting Hamiltonian contains direct qubit-qubit interactions, which have a drastic effect on the ground and excited state properties of such circuits in the ultrastrong coupling regime. In contrast to a superradiant phase transition expected from the standard Dicke model, we find an opposite mechanism, which at very strong interactions completely decouples the photon mode and projects the qubits into a highly entangled ground state. These findings resolve previous controversies over the existence of superradiant phases in circuit QED, but they more generally show that the physics of two- or multi-atom cavity QED settings can differ significantly from what is commonly assumed. [Preview Abstract] |
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T1.00008: A Non-Abelian Geometric Phase for Spin Systems Bharath H M, Matthew Boguslawski, Maryrose Barrios, Michael Chapman Berry’s geometric phase has been used to characterize topological phase transitions. Recent works have addressed the question of whether generalizations of Berry’s phase to mixed states can be used to characterize topological phase transitions. Berry’s phase is essentially the geometric information stored in the overall phase of a quantum system. Here, we show that geometric information is also stored in the higher order spin moments of a quantum spin system. In particular, we show that when the spin vector of a quantum spin system with a spin 1 or higher is transported along a closed path inside the Bloch ball, the tensor of second moments picks up a geometric phase in the form of an SO(3) operator. Geometrically interpreting this phase is tantamount to defining a steradian angle for closed paths inside the Bloch ball. Typically the steradian angle is defined by projecting the path onto the surface of the Bloch ball. However, paths that pass through the center cannot be projected onto the surface. We show that the steradian angles of all paths, including those that pass through the center can be defined by projecting them onto a real projective plane, instead of a sphere. This steradian angle is equal to the geometric phase picked up by a spin system. [Preview Abstract] |
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T1.00009: Effective Field Theory for Strongly Correlated Photonic Matter Michael Gullans, Jacob Taylor, Yidan Wang, Jeff Thompson, Qiyu Liang, Vladan Vuletic, Mikhail Lukin, Alexey Gorshkov A promising route to scaling up quantum information systems is to strongly couple light, or other propagating quantum fields, to localized electronic degrees of freedom in solids or trapped atoms. Describing the emergent non-equilibrium behavior of such strongly coupled light and matter is an outstanding challenge for theoretical physics and quantum information science. A simplifying feature of these systems, however, is that they are often characterized by a large separation of scales between the atomic and photonic degrees of freedom. In this talk, I will discuss recent results where we took advantage of this separation of scales to develop an effective field theory description of interacting photons in cold gases of Rydberg atoms, where the photons become dressed with highly excited Rydberg states. This theoretical approach is analogous to semiclassical nonlinear optics, where the electronic degrees of freedom are integrated out to give rise to effective photon-photon interactions. As an application of this theory, I will show how such Rydberg polariton systems may provide new insights into universality in few-body quantum systems. [Preview Abstract] |
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T1.00010: Ex Vacuo Atom Chips Benjamin Stuhl, Matthew Squires, Spencer Olson, Brian Kasch, Rudy Kohn, Christopher Erickson, Jonathon Crow, Evan Carlson, James Stickney, John Burke We report on recent progress in our group's development of direct-bonded copper atom chip technology. These chips, in conjunction with a custom thin-walled vacuum chamber, allow the production of deep magnetic traps and degenerate Bose gases while keeping the atom chip itself outside of the vacuum envelope. This enables rapid testing of novel chip designs without disturbing either the vacuum quality or the optical alignment of the larger system. [Preview Abstract] |
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T1.00011: Terahertz-frequency magnon-phonon-polaritons in the strong coupling regime Prasahnt Sivarajah, Jian Lu, Keith Nelson, Maolin Xiang, Wei Ren, Shixun Cao, Stanislav Kamba Strong coupling between light and matter occurs when the two interact strongly enough to form new hybrid modes called polaritons. Thus far, the focus of strong coupling physics has been on either the electric or magnetic degrees of freedom, yet the ensuing physics and potential applications motivate the prospect of simultaneously coupling to both. Spintronics, in its quest toward long-range and terahertz (THz) frequency operation, would particularly benefit from such strong coupling because it provides a means for facile transport and interaction with THz spin information. Here we report our results on the strong coupling of both the electric and magnetic degrees of freedom to an ultrafast terahertz frequency electromagnetic wave. In our system, optical phonons in a slab of ferroelectric lithium niobate (LiNbO3) are strongly coupled to a THz electric field to form phonon-polaritons, which are simultaneously strongly coupled to magnons in an adjacent slab of canted antiferromagnetic erbium orthoferrite (ErFeO3) via the THz magnetic field. The strong coupling leads to the formation of new magnon-phonon-polariton modes, which we experimentally observe in the wavevector-frequency dispersion curve in the form of an avoided crossing, and in the time-domain as a normal-mode beating. [Preview Abstract] |
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T1.00012: Towards coupling nitrogen vacancy spins to spin-transfer-driven nanoscale magnetic circuits Adrian Solyom, Zackary Flansberry, Alexandre Bourassa, Jack Sankey, Lilian Childress The nitrogen vacancy (NV) center in diamond is a solid state spin system with long coherence times, with promising applications in quantum information and precision sensing. Optical readout of the spin state allows for the detection of magnetic fields, in principle localized at the nano-scale. Our first goal is to use NV sensors to measure the stray field from magnetic nanocircuits, fabricated on the diamond surface and controlled by spin-polarized currents. Thus far we have fabricated Py/Pt nanowires on single-crystal diamond having a layer of NV centers implanted $\sim$100 nm below the surface. Using the Spin Hall torque from the platinum layer, we can efficiently drive ferromagnetic resonance in the wires, and detect the response via its anisotropic magnetoresistance. We discuss preliminary efforts toward observing spatially- and spectrally-resolved stray fields using nearby NVs, as well as long term considerations for controlling NV centers via related magnetic nanocircuits. [Preview Abstract] |
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T1.00013: Photo-induced charge state switching of the nitrogen-vacancy center in diamond Luke Hacquebard, Loutfi Kuret, Lilian Childress As a strong candidate for quantum computation and metrology applications, the nitrogen-vacancy (NV) defect center in diamond has gained much interest in the solid-state community. The NV center can exist in two different charge states (NV$^0$ and NV$^-$) which have very different optical and spin properties, where typically only the negatively charged state is desired since it provides the triplet ground state used for many experimental applications. Since most experiments involving NV centers use lasers for readout or manipulation it is important to understand the photo-induced charge state ionization and recombination processes at different wavelengths and powers. We developed a charge state readout and initialization method using a 594 nm laser with optimized duration and power, which was used to investigate the ionization and recombination processes from other laser sources. We report charge state switching data from a single NV center when illuminating with 594 nm CW, 532 nm CW, 532 nm pulsed and 766 nm pulsed lasers. We also explore the spin dependence of ionization through the use of applied microwaves. [Preview Abstract] |
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T1.00014: Abstract Withdrawn
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T1.00015: Investigation of the Wave Propagation of Vector Modes of Light in a Spherically Symmetric Refractive Index Profile Preston Pozderac, Cody Leary We investigated the solutions to the Helmholtz equation in the case of a spherically symmetric refractive index using three different methods. The first method involves solving the Helmholtz equation for a step index profile and applying further constraints contained in Maxwell's equations. Utilizing these equations, we can simultaneously solve for the electric and magnetic fields as well as the allowed energies of photons propagating in this system. The second method applies a perturbative correction to these energies, which surfaces when deriving a Helmholtz type equation in a medium with an inhomogeneous refractive index. Applying first order perturbation theory, we examine how the correction term affects the energy of the photon. In the third method, we investigate the effects of the above perturbation upon solutions to the scalar Helmholtz equation, which are separable with respect to its polarization and spatial degrees of freedom. This work provides insights into the vector field structure of a photon guided by a glass microsphere. [Preview Abstract] |
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T1.00016: Engineering matter interactions using squeezed vacuum Sina Zeytinoglu, Atac Imamoglu, Sebastian Huber Virtually all interactions that are relevant for atomic and condensed matter physics are mediated by the quantum fluctuations of the electromagnetic field vacuum. Consequently, controlling the latter can be used to engineer the strength and the range of inter-particle interactions. Recent experiments have used this premise to demonstrate novel quantum phases or entangling gates by embedding electric dipoles in photonic cavities or waveguides which modify the electromagnetic fluctuations. In this submission, we demonstrate theoretically that the enhanced fluctuations in the anti-squeezed quadrature of a squeezed vacuum state allows for engineering interactions between electric dipoles without the need for a photonic cavity or waveguide. Thus, the strength and range of the resulting dipole-dipole coupling can be engineered by dynamically changing the spatial profile of the squeezed vacuum in a travelling-wave geometry. [Preview Abstract] |
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T1.00017: Investigation of Trapped-Ion Heating Rate with Surface Preparation Techniques Jules Stuart, Jonathon Sedlacek, Colin Bruzewicz, Robert McConnell, Jeremy Sage, John Chiaverini Systems of trapped ions are promising candidates for scalable quantum computing applications. The motional states of ion crystals can be used as a bus to transfer entangled states between ions and perform multiple complex quantum operations. Electric field noise tends to heat up the ions in an incoherent way that prevents long sequences of multi-qubit gates. We seek to characterize and reduce this effect by monitoring the heating rate of trapped Sr+ ions in surface electrode traps. We employ surface preparation techniques, including plasma cleaning and ion milling, and analyze the effects on ion behavior. In complementary experiments, we test the effect of a thin dielectric oxide layer deposited on the trap by sputtering and monitored using XPS. We also measure heating rates of co-trapped Sr+ and Ca+ ions in the stretch and common motional modes. [Preview Abstract] |
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T1.00018: Localization of Interacting Particles in a Random Potential Well Khang Pham In many physics textbooks, the authors often show the time-independent view of a single particle interacting with its surrounding. However, only a fraction of the books presents the time-dependent processes. By introducing the time-dependency, the difficulty of solving the Schrodinger equation becomes much more challenging. To solve such equation, the use of numerical methods, which need to be programmed, is often required. Through many trials, we have developed an open source code written in C$++$. In this program, we use the Crank-Nicolson method to solve the Schrodinger equation. Crank-Nicolson is an implicit finite-difference method for solving partial differential equations. The program simulates a particle in a two-dimensional space or a system of two interacting particles. Also, parameters such as mass, initial positions and velocities, and potential can be changed with ease. [Preview Abstract] |
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T1.00019: Disorder Induce the Topological Superfluid in Rashba Spin-Orbit Coupled Fermi Gases Xiaosen Yang We present a theoretical study of the effects of Anderson disorders on the two- and three-dimensional attractive Fermi gases with Rashba spin-orbit coupling. By self-consistent Born approximation approach, we show that the Anderson disorder can induces topological phase transition from topological trivial superfluid phase into nontrivial phase in two dimension case. In three dimension case, the disorder can induce two types of topological nontrivial superfluid phases in which the excitation has gapless nodes. Additionally, the pair coherence length is logarithmic divergent for two dimension case and not divergent for three dimension case. The divergence behavior maybe used to determine the topological phase transition in experiment. [Preview Abstract] |
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T1.00020: Spontaneous dipole-dipole interactions in many-body, driven, dissipative Rydberg systems James Maslek, Thomas Boulier, Eric Magnan, Carlos Bracamontes, Jeremy Young, Alexey Gorshkov, Steve Rolston, Trey Porto We observe unexpected dipole-dipole interactions leading to the violation of a forbidden transition to the 18s manifold of ultra-cold $^{87}Rb$ atoms in a 3D optical lattice, as well as an increase in the linewidth of the allowed two photon rydberg transition. At increasing two photon Rabi frequency, a new resonance appears 10 MHz detuned from the main rydberg transition. Due to the selection rules of the circularly-polarized 2-photon excitation, the $|F=1,m_F=-1>$ state, which lies roughly 10 MHz away, should be inaccessible, and is not present at rabi frequencies less than 60kHz. We interpret this as a mixing of both the accessible and forbidden 18s states, which comes from the dipole-dipole interaction between these states and the populations of nearby p states, which are induced from blackbody decay from the. $|18s,F=2,m_F=-2>$ state. These p states are created faster than the timescales of the experiment, making their effect instant. We observe that the pumping rates of these resonances tend to the same value as the rabi frequency gets large enough, showing a complete mixing of the states. This phenomenon occurs due to the finite lifetimes of rydberg atoms and occurs in highly excited many-body systems. It is relevant for a wide array of proposals, including rydberg dressing [Preview Abstract] |
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T1.00021: Superfluid mixture of a Bose-Einstein condensate and a crossover superfluid Shanshan Ding, Yicai Zhang, Shizhong Zhang In this presentation, I discuss the influence of Boson-fermion interactions in a superfluid mixture consisting of a weakly interacting Bose-Einstein condensate and a fermionic superfluid along BEC-BCS crossover. Within random phase approximation, we calculate how the sound velocity changes with the inter-species interactions; the results are consistent with the analytic calculation in hydrodynamic regime. We further calculate the dynamic structure factor in this superfluid mixture which can be measured using Bragg spectroscopy. Relevance to the recent experiments on superfluid mixture will be commented. [Preview Abstract] |
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T1.00022: Robust entangled states in a non-hermitian periodically driven two-band Bose-Hubbard Hamiltonian Carlos Alberto Parra Murillo, Manuel Humberto Muñoz Arias, Javier Madroñero, Sandro Wimberger The steady state properties of a many-body Wannier-Stark system coupled to an effective reservoir is studied within the non-Hermitian approach in the presence of periodic time-dependent driving. We show how the interplay between dissipation and shaking dynamics reveals a hidden symmetries yielding the occurrence of a (quasi-) loss- and interaction-free subspace. We numerically probe the geometric structure of the asymptotic state and its robustness to imperfections in the preparation of the initial conditions, dissipation and the size of system. [Preview Abstract] |
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T1.00023: Quantum crystallography of Rydberg-dressed Bose gases on a square lattice Wen-Chin Wu, Che-hsiu Hsueh, Makoto Tsubota We numerically investigate the quantum crystallographic phases of a Rydberg-dressed Bose gas loaded on a square lattice by using the mean-field Gross--Pitaevskii model. For a relatively weak lattice confinement, the phases of ground state undergo amorphism, polycrystal, and polymorphism following the increase of the blockade radius, and if the confinement is stronger, a single crystal with a specific filling factor will be formed. In order to distinctively characterize these phases, the structure function is also studied. In such an anisotropic system, we show that the superfluid-fraction tensor should be a measurable quantity, and an anisotropy parameter can be defined. In addition, for such crystallographic phases, the interaction potential can manifest where the grain boundaries appear. [Preview Abstract] |
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T1.00024: A Microscopic Fabry-Perot Cavity for Quantum Optics with NV Centers Erika Janitz, Yannik Fontana, Maximilian Ruf, Mark Dimock, Jack Sankey, Lilian Childress We report on efforts to couple nitrogen vacancy (NV) centers in diamond membranes to optical cavities formed by a microscopic mirror on the tip of an optical fiber and a macroscopic flat mirror. These cavities could dramatically increase the fraction of coherent photons emitted in the NV center zero phonon line (ZPL) at low temperature, which can be used to generate interactions between distant spins. We will present room temperature characterization results from a cavity containing a few-microns thick diamond membrane, where it should be possible to observe cavity coupling to a single NV center via phonon-assisted cavity feeding. At low temperature, the ZPL optical transitions are narrowed and the cavity length must be stabilized to within a cavity linewidth (on the order of 10 pm). We will present our preliminary low temperature fiber cavity designs that should achieve this level of stability using the Pound-Drever-Hall cavity locking technique and a custom vibration isolation platform. [Preview Abstract] |
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T1.00025: Electric field noise in surface ion traps Crystal Noel, Maya Lewin-Berlin, Clemens Matthiesen, Yi Zhou, Hartmut Haeffner Trapped ions provide a suitable platform for quantum information applications due to long coherence times and well-controlled manipulation of their quantum state. In order to scale to many qubits and allow for fast processing, traps are getting smaller and ions are trapped closer to the surface. An unfortunate consequence of this scaling is an increased sensitivity to electric field noise emerging from the surface of the trap electrodes that leads to ‘anomalous heating’ of the ions. We present recent results exploring the frequency scaling of the measured noise as well as novel trap treatment effects. [Preview Abstract] |
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T1.00026: Spreading of waves in disordered media Zilin Ma, Deepak Iyer The localization of classical waves in linear and nonlinear disordered media has been extensively studied in the context of the nonlinear Schr\"odinger equation. Here, we study this phenomenon in the context of other classical systems described by nonlinear equations in the presence of disorder to establish the existence of localization as a generic phenomenon that survives in the presence of nonlinearities. [Preview Abstract] |
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T1.00027: Raising the Bose-Einstein condensation critical temperature using vacancies M.A. Solis, J.G. Martinez, J. Garcia, M. Fortes, P. Salas, O.A. Rodriguez We have studied the thermodynamic properties of an Ideal Bose gas confined within a semi-infinite box with periodic permeable multilayers [1], in particular we have calculated its BEC critical temperature and isochoric specific heat, where we have always observed a critical temperature $T_c$ smaller than the BEC critical temperature ($T_0$) of an infinite homogeneous ideal Bose gas. However, when we introduce a plane vacancy, a finite gap between the ground and first excited states in the particle energy spectrum is introduced, which increases the critical temperature beyond $T_0$ and generates a specific heat jump at $T_c$. We expect that these vacancies could lead to a raise in the critical temperature of superfluids within lattice structures. \noindent [1] P. Salas, et al., PRA {\bf 82}, 033632(2010); O.A. Rodr\'iguez, et al., J. Low Temp. Phys. {\bf 183}, 144 (2016); V.E. Barragan, et al., Int. J. Mod. Phys. B {\bf 30}, 1650099 (2016). \noindent We acknowledge partial support from grants PAPIIT IN107616 and CONACyT 221030. [Preview Abstract] |
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T1.00028: Efficient Non-Resonant Absorption in Thin Cylindrical Targets: Experimental Evidence Andrey Akhmeteli, Nikolay Kokodiy, Boris Safronov, Valeriy Balkashin, Ivan Priz, Alexander Tarasevitch A theoretical possibility of non-resonant, fast, and efficient (up to 40 percent) heating of very thin conducting cylindrical targets by broad electromagnetic beams was predicted in [Akhmeteli, arXiv:physics/0405091 and 0611169] based on rigorous solution of the diffraction problem. The diameter of the cylinder can be orders of magnitude smaller than the wavelength (for the transverse geometry) or the beam waist (for the longitudinal geometry) of the electromagnetic radiation. This can be used for numerous applications, such as pumping of active media of short-wavelength lasers, e.g., through efficient heating of nanotubes with laser radiation. Experimental confirmation of the above results is presented [Akhmeteli, Kokodiy, Safronov, Balkashin, Priz, Tarasevitch, arXiv:1109.1626 and 1208.0066]. Significant (up to 10\%) absorption of microwave power focused on a thin fiber (the diameter is three orders of magnitude less than the wavelength) by an ellipsoidal reflector is demonstrated experimentally. For the longitudinal geometry, experiments provide a confirmation of significant absorption (up to 35\%) of the power of a wide CO2 laser beam propagating along a thin wire (the diameter of the wire can be orders of magnitude less than the beam waist width). [Preview Abstract] |
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T1.00029: Theoretical study on the optical response of silver nanoparticles and array Zhiyu Jiang, Songyou Wang The optical properties of nanoparticles and their arrays are closely related to their surface plasmon resonance. This paper reports a study of optical response of single Ag nanosphere and periodical two-dimensional structure arrays by computer simulation based on the Mie and the multipole resonance theory. For Ag spheres with a radius of less than 40 nm, one observed extinction peak is attributed to electric dipole resonance. For spheres more than 40 nm in radius, apart from the peak contributed by the electric dipole, there is a peak at shorter wavelength, caused by resonance of the electric quadrupole. The electric fields in the particle are weaker than that in the two poles, suggesting the toroidal current in the particle is small and the magnetic dipole and quadrupole resonance contribute little to the extinction efficiency. The simulated results are in accord with the experimental data. For an infinite two-dimensional Ag-nanosphere arrays, two resonance peaks attributed to the dipole resonance of single particle and the Wood-Rayleigh anomalous diffraction were observed. The frequency of multipole resonance can be controlled by tuning the size and the periodicity distribution of the arrays. [Preview Abstract] |
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T1.00030: INSULATORS AND DIELECTRICS |
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T1.00031: Ultra-low coercive field of improper ferroelectric Ca$_{3}$Ti$_{2}$O$_{7}$ epitaxial thin films. Junming Liu, Xiang Li, Lin Lin, Sang-Wook Cheong Hybrid improper ferroelectrics have their electric polarization generated by two or more combined non-ferroelectric structural distortions such as the rotation and tilting of Ti-O octahedral in Ca$_{3}$Ti$_{2}$O$_{7}$ (CTO) family. In this work, we prepare the high quality (010)-oriented CTO thin films on (110) SrTiO$_{3}$ (STO) substrates using pulsed laser deposition. The well epitaxial growth of the CTO thin films on the substrates with the interfacial epitaxial relationship of [001]CTO//[001]STO and [100]CTO//[-110]STO is revealed. The in-plane ferroelectric hysteresis unveils an ultralow coercive field lower than \textasciitilde 5 kV/cm even at low temperature, nearly two orders of magnitude lower than that of bulk CTO single crystals. The huge differences between the epitaxial thin films and bulk crystals is most likely due to the lattice imperfections in the thin films rather than substrate induced lattice strains, suggesting high sensitivity of the ferroelectric properties to lattice defects. [Preview Abstract] |
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T1.00032: Spatial anisotropy of topological domain structure in hexagonal manganites. Junming Liu, Kunlun Yang, Lin Lin, Sang-Wook Cheong The domain structure of hexagonal manganites is simulated based on the phenomenological Ginzburg-Landau theory, and special attention is paid to the evolution of topological vortex-antivortex pattern with the varying out-of-plane anisotropies of two stiffness parameters for the in-plane (\textit{xy}-plane) trimerization amplitude $Q$ and out-of-plane ($z$-axis) polarization $P$. It is revealed that the topological domain structure can be remarkably modulated by the stiffness anisotropies. A larger stiffness for $Q$ along the $z$-axis makes the trajectory lines of the vortex nodes and antivortex nodes to be seriously stretched along the $z$-axis, eventually leading to the topological stripe-like domain pattern. The larger stiffness for either $Q$ or $P$ along the $z$-axis makes the domain walls perpendicular to the $z$-axis wider, while the domain walls parallel to the $z$-axis remain less affected. The present work suggests that the topological domain structure may be controlled by some approaches (e.g. lattice strain) which can change the trimerization stiffness and polarization stiffness in hexagonal manganites. [Preview Abstract] |
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T1.00033: Dielectric characteristics of Mn-doped LaTiO$_{\mathrm{3+\delta }}$ ceramics. Yan Chen, Yimin Cui A series of ceramic composites of Mn-doped La$_{\mathrm{1-}}_{x}$Mn$_{x}$TiO$_{\mathrm{3+}}_{\delta }$ and LaMn$_{x}$Ti$_{\mathrm{1-}}_{x}$O$_{\mathrm{3+}}_{\delta }$ ($x \quad =$ 0.1, 0.2) were synthesized by conventional solid-state reaction method. The low-frequency complex dielectric properties of the composites were investigated as functions of temperature (77 K $\le \quad T \le $ 360 K) and frequency (100 Hz $\le \quad f \le $ 1 MHz), respectively. The dielectric constant of $A$-site doped samples is higher than that of $B$-site doped samples. The loss tangent of low doped samples is much less than that of high doped samples. The $A$-site doped composites exhibit intrinsic dielectric response with a dielectric constant of \textasciitilde 40 in the temperature below 250 K. Interestingly, the dielectric constants of $B$-site doped ceramics increase slightly in the temperature range from 77 to 360 K. And it is clearly observed that extraordinarily high dielectric loss tangent (\textasciitilde 6) appear at low frequency (100 Hz) in LaMn$_{\mathrm{0.2}}$Ti$_{\mathrm{0.8}}$O$_{\mathrm{3+}}_{\delta }$, which is \textasciitilde 8 times larger than that of LaMn$_{\mathrm{0.1}}$Ti$_{\mathrm{0.9}}$O$_{\mathrm{3+}}_{\delta }$, which indicates that the doped content can affect the intrinsic dielectric characteristics significantly. [Preview Abstract] |
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T1.00034: Floquet Spectrum in Weyl semimetal via a One-Photon Resonance Jie Cao Weyl semimetal such as {\$}AsTa{\$} is a new kind of topological material which is protected from small perturbation. In the vicinity of one Weyl point, the linear dispersion indicates that the low-energy excitation is a 3D massless quasi-particle. Usually a photon perturbation could cause a dynamic gap at the resonance energy, however, in Weyl semimetal we find that the dynamic gap stays gapless no matter the form of the perturbation. We also investigate the topology of the dynamic gapless spectrum. [Preview Abstract] |
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T1.00035: Suppression of ferroelectricity in YCrO$_{3}$ Rajeev Gupta, Ashish Garg, Ashish Mall We report the results of temperature dependent X-ray diffraction (XRD) and Raman spectroscopy measurements on YCrO3. X-ray diffraction studies carried out up to 900K and subsequent Rietveld refinement of the data show that there is no evidence of any structural phase transition in YCrO$_{3}$ across the paraelectric to ferroelectric phase transitions ($T_{C\, }$\textasciitilde 470K) and the material retains the orthorhombic structure with \textit{Pnma }space group. Subsequently, temperature dependent unpolarized Raman spectroscopy measurements, from 300 K to 600 K, were carried out to investigate the role of phonons across the $T_{C\, }$. All Raman lines below 600 cm$^{-1}$ are assigned to definite phonon modes of \textit{Pnma }structures on the basis of comparison to a previous experiment at room temperature. For further analysis of the Raman data, the line shape parameters were obtained by fitting a Lorentzian function to each peak. YCrO$_{3}$ shows a strong anomalous temperature variation near $T_{C\, }$in the peak positions and line widths for selected modes as a function of temperature. . [Preview Abstract] |
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T1.00036: Dielectric Relaxation in (BiFeO3)1-x-(KNbO3)x solid solutions Radhe Agarwal, Fan Zheng, Yogesh Sharma, Andrew Rappe, Ram Katiyar We have studied structural, optical and dielectric properties of (BiFeO3)x-(KNbO3)1-x (BFO-KNO) solid solutions with a combination of first principle calculations and experimental methods. Theoretically, we have used density functional theory to predict optical band gap in 40 atom pseudocubic ABO3 type (BFO)1-x-(KNO)x [x$=$0 to 1] supercells. We observed a rhombohedral to orthorhombic type distortion as the doping concentration increased from 0 to 1. For x$=$0.05, we observed a random off center displacements of A-site atoms (Bi, K) from the corresponding oxygen cage (BO6). Such type of behavior can be associated with disruption in long range polar orderings and thus creating short range (nano) polar regions. To further investigate the possibility of dielectric relaxation, we carried out temperature dependent dielectric spectroscopic measurements on (BFO)0.95-(KNO)0.05 bulk ceramics. We observed frequency dependent temperature of permittivity maximum (Tmax) around 540 K. Further, the frequency dispersion in dielectric constant and dielectric loss spectra, and a clear polarization hysteresis near room temperature were observed, which indicate relaxor behavior of (BFO)0.95-(KNO)0.05. Our study leads a way to develop lead free relaxor material, which can be used for various piezoelectric applications. [Preview Abstract] |
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T1.00037: Effect of Bromine Deficiency on the Lattice Dynamics and Dielectric Properties of Alpha-Phase Diisopropyl Ammonium Bromide Molecular Crystals . Ahmad Alsaad, Chris Marin, Nabil Alaqtash, Hsien-Wen Chao, Tsun-Hsu Chang, Chin Li Cheung, Renat Sabirianov Diisopropyl ammonium bromide (DIPAB) molecular ferroelectric crystals exhibiting a large electric polarization (\textasciitilde 23$\mu $C/cm$^{\mathrm{2}})$, a large dielectric constant and a low tangent loss of 0.00068-0.0008 in the $\alpha $-phase. Although XRD shows overall excellent crystallinity, the analysis of vibrational spectra of $\alpha $-DIPAB obtained by FT-IR and Raman spectrometry suggests the presence of disorder in synthesized crystals as indicated by the presence of broad features in Raman spectra. Using vdW $+$ DF2 calculations, we identified majority of vibrational modes present in experimental spectra, specifically analyzing the ones due to Br-disorder. We find that the Br deficiency strongly affects the electric properties of $\alpha $-DIPAB. Particularly, the experimentally measured dielectric constant is large (\textasciitilde 20), while DFT-based calculations of the ideal DIPAB give much smaller values (\textasciitilde 2-3). However, the Br-deficiency leads to a drastic increase of the calculated dielectric constant (\textasciitilde 15-20). Finally, using vdW$+$DF2 method we show that the van der Waals forces have only a slight effect on the structural parameters. [Preview Abstract] |
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T1.00038: Observation of Dirac-Like Semi-Metallic Phase in NdSb. Klauss Dimitri, Madhab Neupane, M. Mofazzel Hosen, Ilya Belopolski, Nicholas Wakeham, Nagendra Dhakal, Jian-Xin Zhu, M. Zahid Hasan, Eric D. Bauer, Filip Ronning The search of new topological phases of matter is one of the new directions in condensed matter physics. Recent experimental realizations of Dirac semimetal phases pave the way to look for other exotic phases of matter in real materials. Here we use a systematic angle-resolved photoemission spectroscopy (ARPES) study of NdSb as well as first-principles calculations to study the electronic structure of NdSb. Our studies reveal two hole-like Fermi surface pockets present at the zone center ($\Gamma )$ point as well as two elliptical electron-pockets present in the zone corner (X) point of the Brillouin zone (BZ). Interestingly, Dirac-like linearly dispersive states are observed about the zone corner (X) point in NdSb. Moreover, the Dirac-like state observed in NdSb may be a novel correlated state, not yet predicted in calculations. Our study opens a new direction to look for Dirac semi-metal states in other members of the rare earth monopnictide family. [Preview Abstract] |
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T1.00039: Transmission line model for channels with spin-momentum locking Shehrin Sayed, Seokmin Hong, Supriyo Datta We will present a simple transmission line model for channels with spin-momentum locking (SML) based on the Boltzmann formalism with four electrochemical potentials [1, 2], which can be used for both time-dependent and steady-state analysis on a wide variety of materials including topological insulators, Rashba interfaces and heavy metals. The model has two components: charge and spin which are coupled by a factor $p_0=\left(M-N\right)/\left(M+N\right)$ representing the degree of SML, where $M$ and $N$ are number of modes for forward moving up and down spins respectively. In normal metal channels ($p_0 = 0$), the charge and spin signals travel at different velocities resulting in spin charge separation. In spin-momentum locked channels, an additional spin signal accompanies the charge signal which suggests a new mechanism in such materials with possible spintronic applications. [1] Hong et al., Sci. Rep. 6, 20325 (2016). [2] Sayed et al., Sci. Rep. 6, 35658 (2016). [Preview Abstract] |
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T1.00040: Growth, transport properties and ARPES measurements of topological Co$_{1-x}$Rh$_{x}$As$_{3}$ and Co$_{1-x}$Rh$_{x}$Sb$_{3}$ single crystals Chaowei Hu, Chang Liu, Bing Shen, Jie Xing, Suyang Xu, Ni Ni Skutterudite materials such as TX$_{3}$ (T= Co, Rh, X=As, Sb, P) have been previously studied for their promising thermoelectric properties. Recently they have been proposed as materials with non-trivial topology. In this poster, we report the growth of Co$_{1-x}$Rh$_{x}$As$_{3}$ and Co$_{1-x}$Rh$_{x}$Sb$_{3}$ using self-flux method. The thermoelectric, transport properties and ARPES measurements of them will be presented. [Preview Abstract] |
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T1.00041: Giant negative magnetoresistance induced by the chiral anomaly in individual Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$ nanowires. Li Caizhen, Wang Lixian, Liu Haiwen, Wang Jian, Liao Zhimin, Yu Dapeng Dirac electronic materials beyond graphene and topological insulators have recently attracted considerable attention. Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$ is a Dirac semimetal with linear dispersion along all three momentum directions and can be viewed as a three-dimensional analogue of graphene. By breaking of either time-reversal symmetry or spatial inversion symmetry, the Dirac semimetal is believed to transform into a Weyl semimetal with an exotic chiral anomaly effect, however the experimental evidence of the chiral anomaly is still missing in Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$. Here we show a large negative magnetoresistance with magnitude of 63{\%} at 60 K and 11{\%} at 300 K in individual Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$ nanowires. The negative magnetoresistance can be modulated by gate voltage and temperature through tuning the density of chiral states at the Fermi level and the inter-valley scatterings between Weyl nodes. The results give evidence of the chiral anomaly effect and are valuable for understanding the Weyl fermions in Dirac semimetals. [Preview Abstract] |
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T1.00042: Prediction of Robust Non-centrosymmetric Topological Dirac Semi-metallic State in Ternary Half-Heusler Compounds Koushik Pal, Umesh Waghmare Topological Dirac semi-metal (TDSM), a novel quantum state of matter with exotic transport, magnetic, chiral and superconducting properties, has been a subject of intense research in recent years. TDSM is a 3-dimensional analogue of graphene, and is also interesting as a parent to other topological states. Although half-Heusler (HH) compounds were shown to exhibit rich topological phases, a robust TDSM phase in them is yet to be discovered. Here, we present a generic topological phase diagram of a large family of HH compounds with strained structures maintaining a three-fold symmetry, and discover their highly robust non-centrosymmetric TDSM state. We show that its symmetry permits a direct control of valley current with parallel electric field. Using an existing, stable half-Heusler LiMgBi as a model system in first-principles theoretical analysis we show that topological semi-metal, topological Dirac semi-metal, normal and topological insulating states are common to strained structure of these HHs which can be realized experimentally through epitaxially grown hetero-structures. Uncovering many HHs exhibiting a variety of topological states, our work opens up exciting phenomena involving chirality, polarity, valley and topology that have the potential for novel technologies. [Preview Abstract] |
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T1.00043: Theory of photoinduced Floquet Weyl semimetal phases Xiao-Xiao Zhang, Tze Tzen Ong, Naoto Nagaosa Weyl semimetal exhibits various interesting physical phenomena because of the Weyl points, i.e., linear band-crossings. We show by Floquet theory that a linearly polarized light applied to a band insulator can induce controllable Weyl points. In a tight-binding model, we classify different types of photoinduced Weyl points that lead to a rich phase diagram characterized by the Chern number defined on each momentum slices of the bulk states. Taking into account the nonequilibrium electron distribution, we calculate and explain the nonmonotonous anomalous Hall conductivity in terms of the light frequency controlled shift of Weyl points' position, which also allows us to examine the conductivity's dependence on the driving electric field. [Preview Abstract] |
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T1.00044: Ferri magnetic fluctuation in Molecular Dirac Fermion System $\rm \alpha \! - \! (BEDT\!-\!TTF)_2 I_3$ Genki Matsuno, Akito Kobayashi In an organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$, a two-dimensional massless Dirac Fermion system is realized under pressure. Because the Dirac Fermion phase is next to the charge ordered phase observed under low pressures, it is expected that electron-electron interaction is relevant even in the Dirac Fermion phase. The sublattice-selective nuclear magnetic resonance measurement have revealed anomalous temperature dependence of the spin susceptibilities under pressure. Below 100K, all component of the Knight shift is heavily suppressed compared to the value expected in a non-interacting Dirac Fermion model. Furthermore, the first evidence of the ferrimagnetic polarization, negative magnetic responce on the B sublattice below 60K, is reported [1]. In this study, we examine the spin susceptibility with random phase approximation in a Hubbard model describing $\alpha$-(BEDT-TTF)$_2$I$_3$. It is found that the ferrimagnetic fluctuation emerges only if there exist cross terms between intra- and inter-band irreducible susceptibilities in the presence of on-site Coulomb repulsion U, reflecting the characteristic phase structure of wave functions in the Dirac Fermion system with multi-sublattices. [1] M. Hirata et al., Nat. Commun. 7, 12666 (2016) [Preview Abstract] |
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T1.00045: Limiting factors for the power conversion efficiency of hybrid organic-inorganic halide perovskite photovoltaic devices under operating conditions. Oscar Granas, Dmitry Vinichenko, Efthimios Kaxiras We use first-principles calculations and thermodynamic modelling to establish that the theoretical maximum efficiency limit is in the range of ~25-27\% under operating conditions. We examine compounds of ABX3 composition, where A={Methylammonium, Methyleniminium, Formamidinium, Guanidinium}, B={Pb,Sn}, X={Br,I} with estimated band-gaps of 0.9 to 2.3 eV. Effective band masses and level alignments for all compounds are determined. Based on this data we setup an effective circuit model for a PIN-cell, including entropic contributions to the free energy of the carriers. Our results indicate that the state-of-the art perovskite based solar cells, due to their intrinsic resilience to defect-induced trap-states and interface quality is already above 80\% of their theoretical maximum efficiency. Our result provide a useful framework for estimating the impact of level alignment to hole and electron transporting materials on the PCE. It also indicates the need for the use of multi-junction cells or hot-carrier extraction in order to reach cells of more than ~27\% power conversion efficiency at room temperature. \footnote{O. Gr\aa n\"as \emph{et al.} Sci. Rep. 6, 36108; doi: 10.1038/srep36108 (2016)} [Preview Abstract] |
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T1.00046: First-principles investigation of charge carrier trapping at surface defects of organic-inorganic hybrid perovskites as photovoltaic materials Hiroki Uratani, Koichi Yamashita Organic-inorganic hybrid perovskites (OIHPs) such as ${\rm CH_3NH_3PbI_3}$ are attracting much interest for photovoltaic application. One of the determining factors of their performance is charge carrier trapping at defects on their surface or grain boundaries. For example, remarkable improvement of photoconversion efficiency from $13.1\,\%$ to $16.5\,\%$ was achieved by surface passivation with Lewis bases due to suppression of charge carrier trapping at surface defects\footnote{N. K. Noel, A. Abate, S. D. Stranks, E. S. Parrott, V. M. Burlakov, A. Goriely, and H. J. Snaith, \textit{ACS Nano} \textbf{8}, 9815 (2014)}. However, the chemical nature of such surface defects (e.g. vacancy or interstitial) is still not well understood. In this work, types of surface defects responsible for charge carrier trapping were clarified by comprehensive first-principles investigation of various types of defects using slab models. It is shown that the defect states originated in Pb-Pb covalent bonding orbitals formed by excessive Pb atoms on OIHPs’ surface are responsible for charge carrier trapping. Our result paves the way for improvement of the photovoltaic performance of OIHPs through rational strategy of suppressing charge carrier trapping at surface defects. [Preview Abstract] |
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T1.00047: Quantifying B Site Disorder in Polycrystalline and Single Crystal Yb$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ Pyrochlore by Quantitative Scanning Transmission Electron Microscopy at Atomic Resolution Zahra Shafieizadeh, Yan Xin, Haidong Zhou The cubic pyrochlore oxides, A$_{\mathrm{2}}$B$_{\mathrm{2}}$O$_{\mathrm{7}}$, have attracted much attention over the past 20 years. A and B ions reside on two distinct interpenetrating lattices of corner-sharing tetrahedral. It has been noticed that the magnetic ground states of Yb$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ are sample dependent. It could have long-range ordered collinear ferromagnetic state, or non-collinear ferromagnetic fluctuations, or short ranged fluctuations. In particular, the specific heat shows sharp peaks at 265 mK for polycrystalline samples, but a broad peak at 214 mK to 250 mK for optical floating zone (OFZ) single crystals. Neutron scattering study shows that OFZ single crystals are lightly stuffed pyrochlore with 2.3{\%} Yb on to Ti sites. We have studied this disorder by quantitative scanning electron microscopy at atomic resolution for both polycrystals and single crystals. We have carried out atomic resolution imaging of Yb$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ along [110] and by comparing image simulations, we have quantified the Yb atoms on the Ti atomic columns, and compared the disorders for both crystals. We also related the degree of the disorder to their magnetic ground states. [Preview Abstract] |
(Author Not Attending)
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T1.00048: Effects of gamma-ray irradiation on the electrical properties of ferroelectric thin films Sang Don Bu, Sam Yeon Cho, Sin Wook Kang We have investigated the effects of gamma-ray irradiation on the electrical properties of ferroelectric thin films such as PbTiO$_{\mathrm{3}}$, Pb(Zr$_{\mathrm{0.52}}$Ti$_{\mathrm{0.48}})$O$_{\mathrm{3}}$, (K$_{\mathrm{0.5}}$Na$_{\mathrm{0.5}})$(Mn$_{\mathrm{0.005}}$Nb$_{\mathrm{0.995}})$O$_{\mathrm{3}}$. The thin films were prepared on Pt/Ti/SiO$_{\mathrm{2}}$/Si substrate using a chemical solution deposition method through a spin-coating process and were subject to gamma-ray radiation at various total doses from 0--3000 kGy. The structural properties as well as the ferroelectric and dielectric properties of the prepared films were examined before and after the gamma-ray irradiation. We found that their crystalline quality did not vary with an increase in the total dose. It was also observed that the remnant polarization value of the films decreased by \textasciitilde 10{\%}, but the films maintained ferroelectricity even after the irradiation up to 3000 kGy. In addition, the dielectric constant of the films decreased gradually with the total dose. The observed variation of the electrical properties on the total dose might be mainly associated with the mobile defects in the thin films such oxygen vacancies and the stored energy gained from the gamma-ray. [Preview Abstract] |
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T1.00049: Bulk and surface electronic structure of hexagonal structured PtBi$_{\mathrm{2}}$ studied by angle-resolved photoemission spectroscopy Qi Yao, Yongping Du, Xiaojun Yang, Yi Zheng, Difei Xu, Xiaohai Niu, Xiaoping Shen, Haifeng Yang, Pavel Dudin, Timur Kim, Moritz Hoesch, ivana vobornik, Zhu-An Xu, Xiangang Wan, Donglai Feng, Dawei Shen PtBi$_{\mathrm{2}}$ with a layered hexagonal crystal structure was recently reported to exhibit an unconventional large linear magnetoresistance. Using angle-resolved photoemission spectroscopy, we present a systematic study on its bulk and surface electronic structure. Through comparison with first-principle calculations, our experiment distinguishes the low-lying bulk bands from entangled surface states. We find significant electron doping in PtBi$_{\mathrm{2}}$, implying a substantial Bi deficiency induced disorder therein. Intriguingly, we discover a Dirac-cone-like surface state without topological protection on the boundary of the Brillouin zone. Our findings exclude linear band dispersion in the quantum limit as the cause of the unconventional large linear magnetoresistance but put support to the classical disorder model from the perspective of the electronic structure. [Preview Abstract] |
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T1.00050: Direct Observation of Large Flexoelectric Bending at the Nanoscale in Lanthanide Scandates Pratik Koirala, Christopher Mizzi, Laurence Marks Large bending of materials can occur at the nanoscale in response to an electric polarization, what is called the flexoelectric effect, but to date this has not been observed directly. Most measurements reported in literature have relied upon the application of a small oscillatory strain gradient to induce. We report here the direct observation of large flexoelectric bending in [110] oriented DyScO$_{3}$ inside an electron microscope. Thin rods of DyScO$_{3}$ bent with under a converging electron beam. The bending was reversible with reduction in beam flux and could be cycled many times. Real time imaging of the bending was complemented with electron diffraction. Similar results were obtained for two other scandates of terbium and gadolinium. Characterization of the surface structure and electronic structure was done using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and reflection electron energy loss spectroscopy. Subsequently, we corroborated these observations with independent ex-situ measurements of the flexoelectric coefficient with a three-point bending setup. The relevant flexocoupling voltage was measured to be -42(2) V, which is higher than expected based upon current flexoelectric models. [Preview Abstract] |
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T1.00051: Infrared induced Hall conductivity measurement of the surface state in 3D TI: experimental development Seongphill Moon, Yang Xu, Ireneusz Miotkowski, Yong P. Chen, Dmitry Smirnov Recently, it has been experimentally demonstrated that irradiation of circularly polarized light with the below-resonant frequency, smaller than the bulk band gap of the 3D TI, can open up a band gap at the Dirac point on the surface state[1]. It is predicted that by shining CP light the quantum hall-like transport phenomena can be observed on the surface of the 3D TI[2]. For doing so, the Fermi level of 3d TI should be placed in between bulk band gap, such as BiSeTeSb2(BSTS)[3]. Inspired by these experimental and theoretical works, we developed the experimental set-up to study out-of-equilibrium magneto-transport of the surface state of 3D TIs under the circularly polarized mid infrared radiation provided by tunable quantum cascade lasers. A detailed description of the experimental apparatus and first results of infrared induced Hall conductivity measurements on BiSeTeSb2 will be presented. [1] K. H. Wang, et al., Science 342, (2013) 453. [2] T. Kitagawa, et al., Phys. Rev. B 84, (2011) 235108 [3] Yang Xu, et al., Nat. Phys$. $\textbf{10}, \quad (2014) 956--963 [Preview Abstract] |
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T1.00052: Engineering topological surface states of Cr-doped Bi2Se3 films by spin reorientation and electric field. Jeongwoo Kim, Seung-Hoon Jhi, Ruqian Wu We propose new ways to achieve the quantum anomalous Hall phase and unusual metal-insulator transition in Cr-doped Bi2Se3 films based on results of model analyses and the first-principles calculations. Using the combination of in-plane and perpendicular components of spins along with electric fields, we demonstrate that the topological state and band structures of TI films exhibit rich possibilities, from the shift of Dirac cones to the opening of nontrivial band gaps. Furthermore, then-plane magnetization leads to the significant suppression of inter-TSS scattering. Our work provides new strategies to obtain the desired electronic structures for the device, complementary to the effort of extensive material search. Work was supported as part of the SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Grant No. SC0012670. Calculations were performed on parallel computers at NERSC supercomputer centers. [Preview Abstract] |
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T1.00053: First Principles Study on Topological-Phase Transition in Ferroelectric Oxides Kunihiko Yamauchi, Paolo Barone, Silvia Picozzi Graphene is known as a 2D topological insulator with zero energy gap and Dirac cone. In this study, we theoretically designed a honeycomb structure of Au ions embedded in a ferroelectric host oxide, in order to exploit structural distortions to control topological properties. We show that the polar structural distortion induces the emergence of spin-valley coupling, together with a topological transition from a quantum spin-Hall insulating phase to a trivial band insulator. The phase transition also affects the Berry curvature and spin-valley selection rules. Analogously to graphene, the microscopic origin of this topological phase is ascribed to a spin-valley-sublattice coupling, which arises from the interplay between trigonal crystal field and an ``effective'' spin-orbit interaction due to virtual excitations between e$_{\mathrm{g}}$ and t$_{\mathrm{2g}}$ states of transition-metal ions. [Preview Abstract] |
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T1.00054: Evolution of the carrier dynamics with quantum transport properties for topological insulator Bi2Se3 as a function of annealing temperature Hanbum Park, Jimin Chae, Kwangsik Jeong, Mann-ho Cho Topological insulator (TI) has conducting surface state with Dirac fermions. Although the novel properties of surface are robust against perturbations, direct observation of the surface carrier dynamics is usually hindered by unintentional doping from bulk defects. Therefore, it is a critical issue in TI research field to distinguish the surface effects from bulk. In this work, we systematically investigated relationship between the surface and bulk states of Bi2Se3 thin films with post-annealing temperature for crystallization of initially grown as [BixSey]n multilayer. As raise the temperature, Bi2Se3 film, a typical TI material, is formed through self-ordering and has n-type states due to Se defects. In this process, we discovered an evolution of band structure including Dirac cone and upward shift of Fermi level from the photoemission studies. We distinguished contribution of the surface and bulk carriers to electrical properties, and investigated the surface-bulk interaction induced quantum transport by magneto-temperature-resistance measurements. In conclusion, crystallization-induced structural modification and increment in an amount of defects lead to enhance the surface-bulk coherent coupling and suppress the intrinsic transport of topological surface. [Preview Abstract] |
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T1.00055: Electron spin resonance of polymer polyvinyl pyrrolidone Doping In Topological Insulator Bi2Se3. yeojin lee, gi wan jeon, kyu won lee, do wan kim, dong min choi, cheol eui lee In this work, we have studied microscopic properties of hydrogen-mediated bismuth selenide by employing electron spin resonance (ESR) measurements. Bismuth selenide was synthesized through hydrothermal co-reduction method with and without a linear polymer polyvinyl pyrrolidone (PVP). An ESR signal is detected only in PVP added bismuth selenide. The ESR intensity of the donor spins can be described in terms of the intrinsic carrier concentration in semiconductors. The ionization energy is obtained to be 47±11meV from the temperature dependency of ESR intensity, which in fact quite compatible to that of hydrogen shallow donors reported in ZnO. [Preview Abstract] |
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T1.00056: Quantum oscillations in metallic Sb$_{\mathrm{\mathbf{2}}}$\textbf{Te}$_{\mathrm{\mathbf{2}}}$\textbf{Se topological insulator} Keshav Shrestha, Vera Marinova, David Graf, Bernd Lorenz, Ching Wu Chu We have studied the magnetotransport properties of the metallic, $p$-type Sb$_{\mathrm{2}}$Te$_{\mathrm{2}}$Se which is a topological insulator. Magnetoresistance shows Shubnikov de Haas oscillations in fields above B$=$15 T. The maxima/minima positions of oscillations measured at different tilt angles with respect to the B direction align with the normal component of field Bcos$\theta $, implying the existence of a 2D Fermi surface in Sb$_{\mathrm{2}}$Te$_{\mathrm{2}}$Se. The value of the Berry phase $\beta =$0.43, determined from a Landau level fan diagram, further suggests that the oscillations result from topological surface states. From Lifshitz-Kosevich analyses, the position of the Fermi level is found to be E$_{\mathrm{F}}=$250 meV, above the Dirac point. This value of E$_{\mathrm{F}}$ is almost 3 times as large as that in our previous study on the Bi$_{\mathrm{2}}$Se$_{\mathrm{2.1}}$Te$_{\mathrm{0.9}}$ topological insulator; however, it still touches the tip of the bulk valence band. This explains the metallic behavior and hole-like bulk charge carriers in the Sb$_{\mathrm{2}}$Te$_{\mathrm{2}}$Se compound. [Preview Abstract] |
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T1.00057: Transfer Matrix Method for Optical Calculations of Multilayered Topological Insulators Ang Chen, Lixin Ge, Yunyun Dai, Lei Shi, Xiaohan Liu, Dezhuan Han, Jian Zi Owing to a topological magneto-electric effect, topological insulators (TIs) show unusual electromagnetic response. As a result, TI films and multilayers possess many interesting and unique optical properties which could offer many important potential applications in designing new functional devices. An efficient method for optical calculations on TI multilayers is thus highly desired. Here, a 4$\times$4 transfer matrix method is developed for optical calculations in layered media consisting of TIs. With the framework of this method, optical properties such as reflection and transmission, and magneto-optical effects such as Kerr and Faraday rotations for different TI-layers are calculated. Unusual photonic band structures and band gaps in TI photonic crystals are also revealed. [Preview Abstract] |
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T1.00058: Tuning surface Dirac valleys by strain in topological crystalline insulators Jianfeng Wang, Lu Zhao, Bing-Lin Gu, Wenhui Duan Topological crystalline insulator has an even number of Dirac cones (i.e., multiple valleys) in its surface band structure, thus potentially leading to valleytronic applications such as graphene. Using the density-functional-theory method, we systematically investigate the strain-induced evolution of topological surface states on the SnTe(111) surface. Our results show that compressive strain can shift the Dirac cones at the $\bar{\Gamma}$ and $\bar{\mathrm{M}}$ valleys to different extents (even oppositely) in energy, while tensile strain can induce different band gaps at the valleys due to the enhanced penetration depths of surface states. Exploiting a strain-induced nanostructure with well-defined edges on the (111) surface, we demonstrate strong valley-selective filtering for massless Dirac fermions by dynamically applying local external pressure. Our findings may pave the way for strain-engineered valley-resolved manipulation of Dirac fermions with high tunability and scalability. [Preview Abstract] |
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T1.00059: Gate-tuned Longitudinal Spin Seebeck Effect in Topological Insulators Victor H. Ortiz, Yadong Xu, Mohammed Aldosary, Cui-Zu Chang, Jing Shi The recent study of the topological spin Seebeck effect (SSE) in magnetic insulator (MI)/topological insulator (TI) heterostructures has raised an interesting question about the Fermi level tuning in the topological surface states of the TI and its effects on the spin Seebeck voltage (V$_{SSE}$). In this work, we fabricate longitudinal SSE devices with a 50 nm Al$_{2}$O$_{3}$ layer prepared by a two-step atomic layer deposition process. In this structure, the heater atop Al$_{2}$O$_{3}$ serves as a top gate as well. The MI/TI heterostructure samples consist of a 20 nm YIG and a 5 quintuple layer thick (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$ (x = 0.25, 0.27, 0.30 and 0.32) TI thin film. As the top gate voltage is swept, the resistance of the TI sample shows expected changes as the Fermi level position is varied. However, as the heater is turned on to measure the SSE response while the gate voltage is simultaneously swept, we find that the V$_{SSE}$/R ratio does not show a significant variation despite the observed change in resistance. We attribute this effect to the insensitivity of the bottom TI surface to top gate voltage. This result also suggests a short spin diffusion length in TI. [Preview Abstract] |
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T1.00060: STRONGLY CORRELATED SYSTEMS, INCLUDING QUANTUM FLUIDS AND SOLIDS |
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T1.00061: Intertwined Order in a Frustrated 4-leg t-J Cylinder John Dodaro, Hong-Chen Jiang, Steven Kivelson We report a density-matrix renormalization group study of the $t$-$J$ model with nearest ($t_1$ & $J_1$) and next-nearest ($t_2$ & $J_2$) interactions on a 4-leg cylinder with concentration $\delta=1/8$ of doped holes. We observe an astonishingly complex interplay between uniform $d$-wave superconductivity (SC) and strong spin and charge density wave ordering tendencies (SDW and CDW). Depending on parameters, the CDWs can be commensurate with period 4 or 8. By comparing the charge ordering vectors with $2 k_F$, we rule out Fermi surface nesting-induced density wave order in our model. Magnetic frustration (i.e. $J_2/J_1 \sim 1/2$) significantly quenches SDW correlations with little effect on the CDW. Typically, the SC order is strongly modulated at the CDW ordering vector and exhibits $d$-wave symmetry around the cylinder. There is no evidence of a near-degenerate tendency to pair-density wave (PDW) ordering, charge 4e SC, or orbital current order. [Preview Abstract] |
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T1.00062: Optical properties of pure and Ru doped mutiferroic material MnTiO3 Rajiv Maurya, Bindu Radhamnay MnTiO3 is a multiferroic material which establishes in the ilmenite structure with the space group R. This material shows a paramagnetic to antiferromagnetic phase transition TN 64K .This material shows a spin op transition at an applied magnetic eld of 6T along the hexagonal c-axis. The linear magnetoelectric effect has been observed in this compound by Mufti et al. The ferrotoroidicity has been observed in the thin lm of this material. The samples were prepared by the conventional solid state route. The samples were characterized using the x-ray diffraction, UV-vis spectrophotometer (Shimadzu, UV-2450) and UV/Vis/NIR spectrophotometer .The x-ray diffraction measurements reveal that the samples are single phase. To understand the optical properties of these materials the UV-vis spectra and DRS spectra were recorded on PerkinElmer UV/Vis/NIR spectrophotometer Lambda 750.The observed spectra show that these compounds show a wide band absorption in visible region. With the increase of doping of Ru at Ti site the absorbance is increasing and the value of max is shifting towards the higher wavelengths. In the Ru doped compounds MnTi0.9Ru0.1O3 and MnTi0.8Ru0.2O3, the value of band gap has been reduced to the 2.25eV and 2.10eV, respectively. The above behaviour suggests that the materi [Preview Abstract] |
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T1.00063: AntiFerromagnetic Heisenberg model on three lattices by a self-consistent Gaussian study Shirin Pourmiri The low temperature dynamics of the classical Heisenberg antiferromagnet with nearest neighbor interaction on three lattices were studied using self-consistent Gaussian approximation(SCGA). It is reported that the results from SCGA method are identical to the Monte Carlo's results. The phase transition temperature(Tc$=$1.37) and critical exponent of susceptibility($\gamma =$1.34) on simple cubic lattice are obtained by applying SCGA method on correlation function. Also the SCGA method is considered on FCC lattice and it is observed that the system cannot find a unique ground state and maintains its geometrical frustration. The effect of weak second-neighbor exchange on the appearance of order in FCC lattice is considered and points in which the antiferromagnetic order arise, are calculated. Moreover XY model on kagome lattice is studied and it's reported that there is no phase transition in this model. But the effect of adding anisotropic term to Hamiltonian is considered and phase transition temperature and critical exponent of susceptibility is obtained through SCGA: Tc$=$0.15, Tc$=$0.28 and Tc$=$0.40 respectively for D$=$0.2,D$=$0.5 and D$=$1 which are well consistent with Monte Carlo simulation. [Preview Abstract] |
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T1.00064: Revisit of the one-dimensional extended Hubbard model by functional renormalization group method Yuan-Yuan Xiang By the recently developed singular-mode functional renormalization group method, we studied the phase diagram of the one-dimensional extended Hubbard model systematically. In our scheme, $p$-wave bond-charge-density wave state and the tri-critical point naturally emerge without any artificial assumption or cutoff. Our phase diagram is consistent with that produced by density-matrix renormalization group method. Besides, we also analyzed the effects of spin-orbit coupling and doping on the various phases. [Preview Abstract] |
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T1.00065: Effect of Molybdenum Doping o the Magnetism Properties of Cobalt Ferrite SRINIVASA RAO SINGAMANENI, Luis Martinez, C. V. Ramana This work investigates the effect of molybdenum (Mo) doping on the magnetic properties of cobalt ferrite (CoFe$_{2}$O$_{4}$, referred to CFO) polycrystalline material. Mo incorporated CFO (CoFe$_{2-}_{x}$Mo$_{x}$O$_{4,\, }$referred to CFMO) ceramics were prepared by solid-state reaction by varying the Mo concentration ($x=$0.0-0.3). X-ray diffraction studies indicate that the CFMO materials crystallize in inverse spinel cubic phase. Mo doping increases the lattice parameter from 8.322 to 8.343 {\AA}. We noticed ferromagnetic-like behavior from all the samples studied, in which, the Curie temperature is found to be close to 300 K. Furthermore, we find almost 2-fold decrease in coercive field (H$_{c})$ from 2143 Oe to 1145 Oe with the increase in Mo doping up to 30{\%}, and is consistently observed at all the temperatures measured (4, 100, 200 and 300 K). In addition, the saturation magnetization estimated at 4 K and at 1.5 T goes through a peak at 92 emu/g (at 15{\%} Mo doping) from 81 emu/g (pristine CFO), and starts decreasing to 79 emu/g (at 30{\%} Mo doping). Our experimental findings led us to believe that the magnetic properties observed here could be due to the complex interplay of double-exchange and super exchange interactions between Fe$^{3+}$/Fe$^{2+}$ via Mo$^{6+}$. [Preview Abstract] |
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T1.00066: Interstitial oxygen as a source of p-type conductivity in RMnO$_{3\, }$hexagonal manganites Sandra Helen Skjærvø, Espen T. Wefring, Silje K. Nesdal, Nikolai H. Gaukås, Gerhard H. Olsen, Julia Glaum, Thomas Tybell, Sverre M. Selbach We use a combination of experiments and first principles electronic structure calculations to elucidate the effect of interstitial oxygen anions, Oi, on the electrical and structural properties of h-YMnO$_{3}$. Hexagonal manganites, h-RMnO$_{3}$ (R $=$ Sc, Y, Ho-Lu) have been intensively studied for their multiferroic properties, magnetoelectric coupling, topological defects and electrically conducting domain walls. Although point defects strongly affect the conductivity of transition metal oxides, the defect chemistry of h-RMnO$_{3}$ has received little attention. Enthalpy stabilized interstitial oxygen anions are shown to be the main source of p-type electronic conductivity, without reducing the spontaneous ferroelectric polarization. A low energy barrier interstitialcy mechanism is inferred from Density Functional Theory calculations to be the microscopic migration path of O$_{i}$. Since the O$_{i}$ content governs the concentration of charge carrier holes, controlling the thermal and atmospheric history provides a simple and fully reversible way of tuning the electrical properties of h-RMnO$_{3}$. [Preview Abstract] |
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T1.00067: Transport and magnetization effects in strain coupled VO$_{\mathrm{2}}$/FeRh heterostructures Steven Bennett, Christian Urban, Juan Trastoy, Ilya Valmianski, Ivan Schuller One of the great challenges of our time is to achieve maximum efficiency in the next generation of low power spintronics. To do so we can turn to inspiration from nature where the energy efficient control of hysteretic processes and exotic phase transitions in biological systems is commonplace. Specifically, the ability to change the magnetic state of a material with a low power electric field opens up a plethora of possible devices in spintronics and memory applications. Here we show the coupling effects between two materials with uniquely controllable phase transitions. VO$_{\mathrm{2}}$ exhibits a metal insulator transition (MIT) as it's structure transitions between T-like monoclinic and rutile, and FeRh has a close to room temperature antiferromagnetic to ferromagnetic phase transition which has been shown to be highly sensitive to interfacial strain. Here we explore how these materials behave as a coupled heterostructure and consider the controllability of these characteristics using electronic stimulation of the MIT. [Preview Abstract] |
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T1.00068: Quest for secondary $\mu $SR signals for Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ using MaxEnt: a Verwey phase transition study. C Boekema, A Colebaugh, A-L Lee, I Lin, A Cabot, C Morante Most muon-spin rotation ($\mu $SR) time series for magnetite (Fe$_{\mathrm{3}}$O$_{\mathrm{4}})$ have been interpreted in terms of \textit{one} $\mu $SR frequency signal. [1] Its Fourier transform appears to confirm this internal magnetic field. Yet many time series show a beat pattern, strongly suggesting a second signal with a close-by frequency. We are searching for secondary signals in zero-field Fe$_{\mathrm{3}}$O$_{\mathrm{4}} \quad \mu $SR data using Maximum Entropy, a recently developed technique [2] more sensitive than curve fitting and/or Fourier transformation. There is also another dilemma namely: the upper signal found for Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ has a local magnetic field larger than the maximum allowable vectorial sum of external and internal contributions. However, the (non)occurrence of secondary signals may shed light on the nature of the Verwey phase transition and its precursors in the Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ Mott-Wigner glass [3] between T$_{\mathrm{v}}$ (123 K) and twice T$_{\mathrm{v}}$ (247 K). [4] Research supported by LANL-DOE, SETI-NASA, SJSU {\&} AFC. [1] C Boekema \textit{et al,} Hpf Interactions 31 (1986) 487; Phys Rev B31 (1985) 1233. [2] C Boekema and MC Browne, MaxEnt 2008, AIP Conf Proc {\#}1073 p260. [3] NF Mott, Metal-Insulator Transitions, Taylor {\&} Francis (1974); C Boekema \textit{et al,} Phys Rev B33 (1986) 210. [4] C Boekema \textit{et al,} Proc 11th Int M2S Conf (2015). [Preview Abstract] |
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T1.00069: Nonlocal, yet translation invariant, constraints for rotationally invariant slave bosons Thomas Ayral, Gabriel Kotliar The rotationally-invariant slave boson (RISB) method \footnote{Lechermann et al., Phys. Rev. B 76, 155102} is a lightweight framework allowing to study the low-energy properties of complex multiorbital problems \footnote{Lanat\`a et al., Phys. Rev. B 85, 035133, Lanat\`a et al., Phys. Rev. X 5, 11008, Lanat\`a et al., arXiv 1606.09614} currently out of the reach of more comprehensive, yet more computationally demanding methods such as dynamical mean field theory.\\ In the original formulation of this formalism, the slave-boson constraints can be made nonlocal by enlarging the unit cell and viewing the quantum states enclosed in this new unit cell as molecular levels.\\ In this work, we extend RISB to constraints which are nonlocal while preserving translation invariance. We apply this extension to the Hubbard model.\\ [Preview Abstract] |
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T1.00070: Thickness driven metal-insulator transition in PLD grown Ga doped ZnO thin films: experiment and first principle studies Joynarayan Mukherjee, B. R. K. Nanda, M. S. Ramachandra Rao Electrical transport properties of Ga doped ZnO thin films, grown using pulse laser deposition technique, are investigated as a function of thickness (6 -- 75 nm) and further substantiated through density-functional calculations. We find that while the thinnest film exhibits a resistivity of 0.05 ohm-cm, lying on the insulating regime, the thickest has resistivity of 4.8 x 10$^{-4}$ ohm-cm to make the system metallic. Our analysis reveals that the Mott-VRH model governs the insulating behavior in the thinner Ga:ZnO whereas the weak localization theory is appropriate to explain the metallicity in the thicker Ga:ZnO. Complementing the experiment through first principle calculations on two extremes -- 2 unit cell film (1.04 nm) and bulk, we show that for the film, crystalline disorder sets in with Ga doping which in turn creates highly localized states in the vicinity of the Fermi level (EF) and restrict the electron mobility. Such is not the case with bulk, where EF is occupied with a dispersive band carrying the electron donated by the dopant. [Preview Abstract] |
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T1.00071: Variational Mean-field approach to three-body bound states in many- body systems Yashar Komijani, Piers Coleman Motivated by recent dynamical mean-field theory studies on the Hubbard model [Sakai et al., Phys. Rev. B 94, 115130 (2016)], we study the formation of symmetry-breaking three-body bound states in interacting systems. We introduce a new many-body approach, involving resonant Weiss fields that inject a test bound-state into the three body channel. Using a three-body adaptation of Feynman's variational mean-field approach, we are able to put a rigorous bound on the ground state energy of a state with three-body resonances that can be used as the basis for a new kind three-body Hartree Fock approach. This talk will present these new results and will discuss our ongoing efforts to apply it to physical systems, including Abrikosov-Suhl resonance formation in the Anderson impurity model and d-wave superconductivity in the Hubbard model. [Preview Abstract] |
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T1.00072: V$_3$O$_5$: Insulator-metal transition and electric-field-induced resistive-switching Bertina Fisher, Larisa Patlagan, K. B. Chashka, C. Makarov, G. M. Reisner Resistive-switching in oxides exhibiting insulator-metal-transitions (IMT) has many potential applications when the transition temperature (T$_{IMT}$) is above room temperature (RT). V$_3$O$_5$ is one of two vanadium oxides that exhibit IMT above RT (T$_{IMT}$=428 K); the other is VO$_2$ (T$_{IMT}$=340 K). We report on DC I-V characteristics of polycrystalline samples and single-crystals of V$_3$O$_5$ over wide ranges of currents. For all samples self-heating induced hysteretic nonlinear conductivity, followed at higher currents by onset of negative differential resistivity regime and finally, at highest currents, by switching to the metallic state. Self-heating was monitored by comparing R(V)=V/I obtained from I(V) with R(T) measured using low currents. Slow switching towards a partially transformed state with prolonged memory is typical of polycrystalline samples. High currents applied in the metallic state of one of the single crystals affected the oxygen content of the material and even caused appearance and disappearance of a VO$_2$ inclusion. Simple and reproducible I-V plots were obtained for a single crystal with currents that barely induced the metallic state. [Preview Abstract] |
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T1.00073: Abstract Withdrawn
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T1.00074: Time-resolved photoemission of a nonequilibrium charge-density-wave-ordered system Oleg Matveev, Andrij Shvaika, Thomas Devereaux, James Freericks We examine the response of an electronic charge-density-wave-ordered (CDW) system in a time-resolved pump-probe photoemission spectroscopy experiment. In this experiment, the system is driven out of the equilibrium by a high intensity but low frequency pump pulse and then photoexcited by a low intensity but high frequency probe pulse. The system we examine is the half-filled Falicov-Kimball model, which has an exact solution within dynamical mean-field theory. This system has an interesting quantum critical point in the ordered phase, which is insulating at $T=0$, but is metallic for all $T>0$. Interestingly, the quantum critical CDW cannot be pumped easily --- whatever energy is pumped in during the leading edge of the pump pulse is pumped out on the trailing edge. When one is in the weakly correlated insulator or the strongly correlated insulator, the system is much more easily pumped. These features occur only within the ordered phase. [Preview Abstract] |
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T1.00075: Coupling the spin resonance states in a carbon nanotube quantum dot to a dissipative environment Matthew Meers, Gu Zhang, Chung Ting Ke, Henok Mebrahtu, Alex Smirnov, Harold Baranger, Gleb Finkelstein When a resonance level couples to a dissipative environment, electrons tunnel only with a specific spectral function. Previously, we have restored single channel conductance by fine tuning the symmetry of tunneling barriers and the position of the resonance level with the spin degree of freedom. From this restoration of $e^2/h$, a quantum critical point and quantum phase transition can be observed. We study a series of devices with dissipation strengths of r =0.1, 0.3, 0.5 and 0.75 at zero field, where r is $R_{Lead}/$R_q$, ($R_q$=$h/e^2$). A peak bending feature is observed, which indicates a non-fixed point on a RG flow diagram. In addition, peak shifts change with temperature, especially for higher dissipation samples. This may indicate the restoration of an RG fixed point at higher temperature. We further explore the Kondo regime for spin ½ and singlet-triplet in the even valley. In a dissipative environment, the $T_K$ is highly suppressed and spin ½ Kondo can be only observed for r=0.1. When r $\geq$ 0.3, spin ½ Kondo is not observable. This may be due to the exponential decay of $T_K$ in the dissipation strength r. However, a spin singlet-triplet Kondo is observed for r=0.5. By fitting to our data to theory, we find that $T_{KS-T}$ can be higher than $T_{K-1/2}$ for r=0.5 [Preview Abstract] |
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T1.00076: Evidence of Phase Transitions in MoO$_{\mathrm{2}}$ single crystals Mario da Luz, Leandro Alves, Felipe Oliveira, Bruno Lima, Carlos dos Santos, A. Rebello, Sueli Masunaga, John Neumeier, Juscelino Leão, Carlos Giles In this work, physical and structural properties are revisited in the MoO$_{\mathrm{2}}$ compound. MoO$_{\mathrm{2}}$ single crystals were grown by chemical vapor transport. Heat capacity and electrical resistance as a function of temperature were performed using a 9 T cryo-free Physical Properties Measurement System (PPMS). Thermal expansion (TE) was measured using a high-resolution capacitive dilatometer cell constructed from fused quartz. High-resolution Synchrotron x-ray powder diffraction was measured using a Shimazu diffractometer (XRD 6000) at several temperatures in the Brazilian Synchrotron Light Laboratory. Furthermore, Neutron powder diffraction data were collected using the BT-1 32 detector neutron powder diffractometer at the NIST. Electrical resistivity, heat capacity, and TE measurements show two clear features near 220 K and 267 K suggesting two phase transitions in MoO$_{\mathrm{2}}$ compound. The transition at \textasciitilde 267 K has been related to a structural phase transition by high resolution synchrotron x-ray diffratometry measurements. Low temperature neutron diffraction measurements suggest that the phase transition near 220 K is electronic or magnetic in nature. [Preview Abstract] |
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T1.00077: Investigation of Broken Time Reversal Symmetry in Pr-concentrated side of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ P.-C. Ho, D. E. MacLaughlin, M. B. Maple, L. Shu, O. O. Bernal, A. D. Hillier, T. Yanagisawa One of the intriguing features that indicate unconventional superconductivity (SC) in the filled skutterudite compound PrOs$_4$Sb$_{12}$ is the broken time reversal symmetry (TRS)[1]. Previously in our muon spin relaxation ($\mu$SR) study on the influence of the Nd$^{3+}$ moment in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$[2], we found that the magnetism extends deep in the SC state for $0.45 \le x \le 0.55$ and a strong $\mu^+$ dynamic rate in $x = 0.25$ possibly resulting from significant Nd moment fluctuations. In our most-recent results of $\mu$SR experiments in the x=0.05 and 0.1 samples, at zero magnetic field, a combined exponential and Gaussian relaxation behavior was found. The exponential rate has a strong temperature dependence below $T_c$, which may originate from spontaneous supercurrents or spin texture due to broken TRS. [1] Y. Aoki et al., PRL 91, 067003 (2003). [2] D. E. MacLaughlin et al., PRB 89, 144419 (2014). [Preview Abstract] |
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T1.00078: Ferromagnetic quantum criticality in Sm$_{1-x}$La$_{x}$NiC$_{2}$ (x$=$0.85, 0.92 and 0.96) Wonjun Lee, Suheon Lee, Tuson Park, K.-Y. Choi We report \textmu SR experiments on the ternary compounds Sm$_{1-x}$La$_{x}$NiC$_{2}$ (x$=$0.85, 0.92, and 0.96), possessing a non-centrosymmetric orthorhombic CeNiC$_{2}$ structure (Amm2). The end members of these compounds have the ferromagnetic (FM) and charge-density-wave states at x$=$0 and the superconducting (SC) state at x$=$1. A FM quantum criticality (QC) is anticipated to occur around x$=$0.92. The x$=$0.96 SC sample exhibits a linear T dependence of the muon relaxation rate $\lambda_{muon}$, giving no indication of time-reversal symmetry breaking unlike the x$=$1 sample. ZF-\textmu SR measurements of the x$=$0.85 FM sample show a steep increase of $\lambda_{muon}$ below 5 K without obvious muon-spin precession, suggesting the formation of an inhomogeneous, weak magnetic ordered state. Longitudinal field-\textmu SR experiments unveil an ordered volume fraction of about 56 {\%}. For a case of the putative x$=$0.92 QC compound, the static fraction is decreased to 15 {\%}, while $\lambda_{muon}$ extracted from the ZF-\textmu SR spectra display ``persisting spin dynamics''. This suggests that the x$=$0.92 sample is close to QCP. [Preview Abstract] |
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T1.00079: Non-Fermi-liquid at (2+1)d ferromagnetic quantum critical point Xiao Yan Xu, Kai Sun, Yoni Schattner, Erez Berg, Zi Yang Meng Itinerant quantum critical points (QCPs), existing in heavy-fermion materials and transition-metal alloys, have constantly attracted people's attention. The reason of the intensive focus, partially, is that controlled investigation of such systems have been proved extremely difficult and consensus has not be reached. Attempts to analytically treat the problem, starting from the celebrated Hertz-Millis-Moriya framework, have provided valuable insights, but a full, controlled solution is still lacking. Here, we design a quantum Monte Carlo technique, that can study the itinerant QCP in an unbiased manner. By constructing a ferromagnetic QCP with Fermi surface coupled to ferromagnetic bosonic critical fluctuations, we have successfully realized a continuous quantum phase transition in itinerant ferromagnet in (2+1)d. Interestingly, at the QCP, clear signature of non-Fermi-liquid behavior in the fermion propagators manifests. Due to the coupling between fermions and bosonic modes, the (2+1)d ferromagnetic universality has also been found neither the naive bosonic one (i.e., (2+1)d Ising) nor the Hertz-Millis-Moriya prediction. [Preview Abstract] |
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T1.00080: Testing the validity of the Fisher-Langer relation in the vicinity of a quantum critical point Timothy Elmslie, Derrick VanGennep, Daniel Jackson, Dmitrii Maslov, James Hamlin Fisher and Langer pointed out that, in the vicinity of a magnetic order-disorder transition, the magnetic part of the specific heat and the temperature derivative of the electrical resistivity should be proportional to each other. This behavior has been observed in a wide variety of systems. However, it is unknown if this scaling relation remains valid as the system is tuned towards a quantum critical point. I will present our recent experiments aimed at testing the validity of the Fisher-Langer relation in the vicinity of a disorder-driven ferromagnetic quantum critical point. [Preview Abstract] |
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T1.00081: Magnetocrystalline anisotropy and magnetic properties of rare-earth dialuminides. Timothy Hackett, D. Paudyal, V. K. Pecharsky We report here how the electronic structure and magnetocrystalline anisotropy play a role in the magnetic and structural transformations of rare-earth dialuminides. In addition, we also present the delicate balance between the spin and orbital magnetic moments and their effect on these transformations. We have employed predictive advanced density functional theory calculations including Hubbard model for onsite 4f electron correlation and spin orbit coupling for magnetocrystalline anisotropy. The predicted magnetostructural properties have been validated from experiments. Although the cubic Laves phase structure is fairly isotropic, our theoretical and experimental studies reveal that most of the rare earth dialuminides undergo high temperature paramagnetic to the low temperature ferromagnetic transition with coupled or decoupled structural transformations. Calculations show that crystal field split localized 4f and crystal field and exchange split delocalized 5d states are responsible for the magnetostructural transformations in these dialuminides. [Preview Abstract] |
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T1.00082: Theoretical study on polarization effect in resonant x-ray emission spectroscopy for $3d$ systems Takayuki Uozumi The $3d$ systems show a rich variety of fascinating phenomena, such as superconductivity and magnetism, caused by strong correlation among $3d$ electrons. X-ray spectroscopy, such as x-ray photoemission spectroscopy (XPS) and resonant x-ray emission spectroscopy (RXES), has been a powerful technique to investigate the electronic state of the $3d$ systems. Especially, recent experimental progress in the energy resolution and in the use of incident-photon polarization has enabled us to observe the spectral fine features in the $2p$ XPS and $2p$-$3d$-$2p$ RXES, which are reflecting intrinsic characters of the correlated valence electrons. Concerning the analysis of the $2p$ XPS, we have developed a theoretical framework based on the impurity Anderson model considering dynamical mean field (EPL, {\bf 114} (2016) 27003). In this presentation, we treat mainly the $2p$-$3d$-$2p$ RXES, paying attention on the polarization dependence. Actually, we show the RXES results for typical $3d$ systems, such as TiO$_2$, LaMnO$_3$ and NiO, and discuss the possibility of experimental determination of final-state multiplet characters from the polarization dependence, based on the RXES function decomposed into the excitation paths with an irreducible tensor form for single- and polycrystals. [Preview Abstract] |
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T1.00083: Thermodynamics of disordered Heisenberg model Michael Mulanix, Ehsan Khatami Using numerical linked-cluster expansions, we study the thermodynamic properties of the disordered Heisenberg model on the square lattice. We implement a new technique for treating continuous disorder within the NLCE and obtain results for the energy, entropy, specific heat, and spin correlations in the thermodynamic limit. [Preview Abstract] |
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T1.00084: Emergence of the Isotropic Kitaev Honeycomb Lattice with Two dimensional Ising Universality in $\alpha $\textbf{-RuCl}$_{\mathrm{\mathbf{3}}}$ Seung-Hwan Do, Sang-Youn Park, Kwang-Yong Choi, D. Jang, T. -H. Jang, J. Schefer, C.-M. Wu, J. S. Gardner, J. M.S. Park, J. -H. Park, Sungdae Ji The Quantum Spin Liquid(QSL) state is indeed exactly derived by fractionalizing the spin excitation into spinless Majorana fermions in a perfect two-dimensional (2D) honeycomb lattice, so-called Kitaev lattice, and its experimental realization is eagerly being pursued. Here we report the Kitaev lattice stacking with van der Waals (vdW) bonding in a high quality $\alpha $-RuCl3 crystal using x-ray and neutron diffractions. Even in absence of apparent monoclinic distortion, the system exhibits antiferromagnetic (AFM) ordering below 6.5 K, likely due to minute magnetic interaction from trigonal distortion and/or interlayer coupling additionally to the Kitaev Hamiltonian. We also demonstrate 2D Ising-like critical behaviors near the Néel temperature in the order parameter and specific heat, capturing the characteristics of short range spin-spin correlations underlying the Kitaev model. Our findings hold promise for unveiling enigmatic physics emerging from the Kitaev QSL. [Preview Abstract] |
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T1.00085: Ground state properties of the ANNNI model in a transverse field: A quantum fidelity approach O. Bonfim, Beatriz Boechat, J. Florencio We analyze the ground-state properties of the {\$}s$=$1/2{\$} one-dimensional ANNNI model in a transverse field using the approach of quantum fidelity. We numerically determine the fidelity susceptibility as a function of the transverse field ({\$}B\textunderscore x{\$}) and the strength of the nearest-next-neighbor interaction ({\$}J\textunderscore 2{\$}) for systems of up to 24 spins. By analyzing the ground-state eigenvectors of finite systems, we expect that at the thermodynamic limit, the system will have an infinite number of phases, a ferromagnetic phase, a kink phase, an infinite number of modulated phases, floating phase and an antiphase. [Preview Abstract] |
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T1.00086: Structural disorder study of d- and f-metals close to ferromagnetic quantum critical point Jean-Guy Lussier, Adane Gebretsadik, Ruizhe Wang, Almut Schroeder, Katharine Page We present low temperature neutron diffraction data and pair distribution function analysis of two ferromagnetic alloys which can be driven to a paramagnetic phase by chemical substitution. Both series show indication that magnetic inhomogeneities like magnetic clusters play an important role for this magnetic quantum phase transition. All Ni$_{1-x}$V$_x$ polycrystalline samples up to $x=15\%$ crystallize in a single phase, random alloy FCC structure. The increase of lattice constant and the atomic displacement parameter can be explained by a random occupation of V- and Ni-ions on the lattice with a radius ratio of 1.05. This is sufficient to explain the magnetic cluster formation. All polycrystalline CePt$_{1-x}$Rh$_x$ samples as well as CePd$_{1-x}$Rh$_x$ samples with $0.2\leq x \leq 0.8$ crystallize in the CrB structure. The change of lattice constants and atomic displacement parameters towards higher $x>0.5$ indicate a large variation in Ce-Rh bond lengths. This disorder is created by the different Ce neighbor atoms, indicating Ce is mixed valent. (experiments performed at LANSCE, Los Alamos National Laboratory and SNS, Oak Ridge National Laboratory) [Preview Abstract] |
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T1.00087: Laughlin's argument for the quantized thermal Hall effect Ryota Nakai, Shinsei Ryu, Kentaro Nomura We have studied an application of the Laughlin's magnetic-flux-threading argument for the quantized thermal Hall effect. Owing to the analogy between electromagnetism and gravito-electromagnetism, there is one-to-one correspondence between Laughlin’s argument for the quantum Hall effect and that for the quantized thermal Hall effect. The gravitational counterpart of the magnetic flux induces the global diffeomorphism anomaly of the chiral boundary modes, and simultaneously adiabatic motions of the bulk quantum Hall states. These phenomena directly lead to the quantized thermal Hall effect. [Preview Abstract] |
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T1.00088: An explanation for the pseudogap states and the quantum phase transitions beneath the Dome Alejandro Genaro Cabo Montes de Oca, Yoandris Vielza de la Cruz, Mauricio Domingues A model is presented to improve the understanding of the normal state of cuprate superconductors. The analysis reproduces the AF correlations and insulator character of these materials. The discussion also led to an outstanding prediction: the existence of well defined pseudogap states, which physical origin constitutes still today a debated question. The pseudogap phase emerges as a paramagnetic excited state, breaking the square crystal symmetry of the CuO planes in the same way as the AF order does it in the material. The results defined the pseudogap effect as being of pure Coulomb origin. The Fermi surface exhibits the property defining its name: a momentum dependent gap, that closes at the four corners of the Brillouin cell. The effect of the hole doping on both the AF-Insulator and the pseudogap states was investigated. Surprisingly, the evolution of the energy and band structure with hole doping, became able to predict the quantum phase transition (QPT) which La2CuO4 and other cuprate materials show at doping value, laying ``beneath'' the superconductor ``Dome''. The energies of the insulator and pseudogap states, both tend to coincide at a critical doping value of 0.2, at which the QPT is observed in the material. [Preview Abstract] |
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T1.00089: COMPLEX STRUCTURED MATERIALS, INCLUDING GRAPHENE |
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T1.00090: Enhanced Chemical Vapor Sensing with MoS2 Using 1T/2H Phase Contacts/Channel Adam Friedman, Paul Campbell, Keith Perkins, James Culbertson, Aubrey Hanbicki Transition metal dichalcogenides show remarkable potential for use in chemical vapor sensor devices. They are inexpensive, inherently flexible, low-power, can be grown in large areas, and have shown high sensitivity and selectivity to electron donor analyte molecules important for explosives and nerve gas detection. However, for most devices the conductance response is dominated by Schottky contacts, to the detriment of the sensitivity and obscuring the intrinsic sensing capability of the devices. We use contact engineering to transition the contacts in a MoS2 FET-based chemical vapor sensor to the 1T conducting phase, leaving the channel in the 2H semiconducting state, thus providing functional Ohmic contacts to the device. We show that the resultant sensors have greatly improved electrical characteristics, are more selective, and recover fully after chemical vapor exposure—all major improvements to previous MoS2 sensor devices. We identify labile nitrogen-containing electron donors as the primary species that generate a response in MoS2, and we study the dynamics of the sensing reactions identifying two possible models for the chemical sensing reaction. [Preview Abstract] |
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T1.00091: Energy gap states and tunneling currents in semiconducting graphene Dominik Szczesniak, Ross Hoehn, Sabre Kais It has been predicted that when graphene is supported on a substrate or doped with foreign atom species, the inherent linear electronic dispersion of its pristine form can be strongly altered. Worthy of special attention is the situation when the interactions between graphene and the substrate or dopants lead to an opening of the finite electronic gap in the fermionic spectrum of this nano-material, and strongly influence its transport and optical properties. Herein, the fundamental electronic transport properties of such perturbed graphene are discussed in the framework of the complex band structure analysis, which not only accounts for the propagating but also the evanescent electronic states. Various scenarios responsible for the band gap opening and manipulation of its characteristics are considered, these considerations may entirely account for the aforementioned perturbations to the pristine graphene. It is shown, that the these perturbations are responsible for inducing gap states which allow electrons to directly tunnel between the conduction and valence bands in perturbed graphene. The resulting tunneling states are analyzed in a comprehensive manner, suggesting their great importance for the transport processes across graphene-based semiconducting nanostructures. [Preview Abstract] |
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T1.00092: Electronic Properties of Curved and Defective 2-D BN Nanostructures Kory Beach, Humberto Terrones, Aldo Raeliarijaona, Ross Siegel, Fred Florio Density functional theory (DFT) with local density approximation (LDA) pseudopotentials is used to calculate the band structure and density of states of various novel 2-D BN nanostructures. Three types of systems are studied: Schwarzites, a Haeckelite, and an h-BN monolayer. Schwarzites are negatively curved structures in which the curvature is due to the introduction of octagonal rings of alternating boron and nitrogen atoms. In particular, three families of Schwarzites are analyzed: P, G and IWP. The Haeckelites on the other hand, are flat layers composed of squares and octagons of BN. It is found that all these BN allotropes are metastable in which the band gap is direct and smaller than the most stable system, h-BN. [Preview Abstract] |
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T1.00093: Reflection of Low Energy Positrons from the Surface of Highly Oriented Pyrolytic Graphite and Single Layer Graphene. S.K. Imam, V. A. Chirayath, M. D. Chrysler, A. J. Fairchild, R. W. Gladen, A.R. Koymen, A.H. Weiss A time of flight positron annihilation induced Auger electron spectrometer (TOF-PAES) was utilized to measure the reflection of positrons as a function of incident positron energy (0 to 10 eV) from the surface of highly oriented pyrolytic graphite (HOPG) and from a single layer graphene (SLG) on a Cu foil. A NaI scintillation detector was used to measure the annihilation gamma from the reflected positrons as a function of incident positron kinetic energy. The annihilation of the positrons on HOPG and SLG were simultaneously measured using another NaI detector near the sample. The Auger electrons emitted as a result of the annihilation of positrons from the surface of the sample were also measured concurrently. As the positron kinetic energy was increased, the number of reflected positrons calculated from the intensity under the annihilation gamma peak showed a steady decrease. The positronium formation measured at the sample using the gamma spectrum showed a peak at \textasciitilde 6 eV. The intensity of the carbon KVV Auger peak showed a dip at the same energy. The correlation of the three signals, intensity of reflected positrons, positrons annihilating at the sample and the Auger intensity are discussed for both samples. [Preview Abstract] |
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T1.00094: Synthesis of Monolayer MoS$_{\mathrm{2}}$ by Chemical Vapor Deposition Sajeevi Withanage, Mike Lopez, Kenneth Dumas, Yeonwoong Jung, Saiful Khondaker Finite and layer-tunable band gap of transition metal dichalcogenides (TMDs) including molybdenum disulfide (MoS$_{\mathrm{2}})$ are highlighted over the zero band gap graphene in various semiconductor applications. Weak interlayer Van der Waal bonding of bulk MoS$_{\mathrm{2}}$ allows to cleave few to single layer MoS$_{\mathrm{2}}$ using top-down methods such as mechanical and chemical exfoliation, however few micron size of these flakes limit MoS$_{\mathrm{2}}$ applications to fundamental research. Bottom-up approaches including the sulfurization of molybdenum (Mo) thin films and co-evaporation of Mo and sulfur precursors received the attention due to their potential to synthesize large area. We synthesized monolayer MoS$_{\mathrm{2}}$ on Si/SiO$_{\mathrm{2}}$ substrates by atmospheric pressure Chemical Vapor Deposition (CVD) methods using sulfur and molybdenum trioxide (MoO$_{\mathrm{3}})$ as precursors. Several growth conditions were tested including precursor amounts, growth temperature, growth time and flow rate. Raman, photoluminescence (PL) and atomic force microscopy (AFM) confirmed monolayer islands merging to create large area were observed with grain sizes up to 70$\mu $m without using any seeds or seeding promoters. These studies provide in-depth knowledge to synthesize high quality large area MoS$_{\mathrm{2}}$ for prospective electronics applications. [Preview Abstract] |
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T1.00095: Electronic structure and lattice dynamics of few-layer InSe Lucas Webster, Jia-An Yan Studies of Group-III monochalcogenides (MX, M = Ga and In, X = S, Se, and Te) have revealed their great potentials in many optoelectronic applications, including solar energy conversion, fabrication of memory devices and solid-state batteries. Among these semiconductors, indium selenide (InSe) has attracted particular attention due to its narrower direct bandgap, which makes it suitable for photovoltaic conversion. In this work, using first-principles calculations, we present a detailed study of the energetics, atomic structures, electronic structures, and lattice dynamics of InSe layers down to two-dimensional limit, namely, monolayer InSe and bilayer InSe with various stacking geometry. Calculations using various exchange-correlation functionals and pseudopotentials are tested and compared with experimental data. The dependence of the Raman spectra on the stacking geometry and the laser polarization will also be discussed. [Preview Abstract] |
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T1.00096: Reduction of Graphene Oxide studied with FTIR Heike Geisler, Jacob Bachor, Nicolas LaScala Graphite oxide was successfully synthesized from graphite powder using the modified Hummers method*. The graphite oxide was then exfoliated to yield graphene oxide, which was subsequently reduced to give reduced graphene oxide. This employed two different chemical reduction methods, and one effective combination of the two. The two methods being a weaker sodium borohydride/calcium chloride catalyst and a hydrogenation through hydrogen produced from the reaction of hydrochloric acid and aluminum. This can be seen through the removal of various functional groups from our graphene oxide sample after each reduction method, as shown in FTIR spectra of each sample. While the reduction methods employed did remove a number of oxygenated functional groups on the graphene oxide sheet, we still observe the presence of hydroxyl and some carboxylic acids that persist through. We also notice the appearance of a well-defined peak at \textasciitilde 1600 cm-1 representing the conjugated system in the combined reduction method. * W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc., 1958, 80, 1339 [Preview Abstract] |
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T1.00097: Noise Analyses of NV Center Diamonds due to Bulk and Surface Effects Matthew Moore, Deborah Santamore, Yahui Xiao, Du Wang, Shamia Pamplin Nitrogen-vacancy (NV) center diamonds have seen tremendous applications in emergent quantum technologies including ultra-high resolution magnetic field sensors. However, coherence time and sensitivity of NV-based devices are limited by noise that causes decoherence and line broadening. We theoretically investigate the noise caused by the electric field and thermal fluctuations, which can be present naturally or in the presence of a laser. We examine the effects of charge fluctuations on the surface as well as strains caused by impurity contaminations in bulk diamond and surface contaminations, which can be present from the synthesis of NV centers and surface interactions with the environment. We derive the stochastic master equation from the Hamiltonian and analyze the noise spectrum for each cause. We also quantify thermal noise and its effect using the fluctuation-dissipation theorem. [Preview Abstract] |
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T1.00098: First-principles Study on Early Stage of Graphene Growth on SiC substrate by Si Sublimation. Jun Nara, Takahiro Yamasaki, Takahisa Ohno Graphene is known to have characteristic physical properties, such as high electron mobility and structural robustness, and then expected as future electronic device materials. Graphene growth on SiC substrate by Si sublimation is one of the promising graphene growth methods. However, the growth mechanism, especially, its early stage is not clear yet. In this study, we investigate the atomistic growth mechanism of the graphene growth by using first-principles molecular dynamics simulations. We used the PHASE/0 code [1] in this study. We found the remnant C atoms on SiC substrate after the Si sublimation preferably form one-dimensional (1D) structures than two-dimensional (2D) structures. Then, 2D structures are formed by the gathering of 1D structures. This is possible because 1D structures easily diffuse on the surface, differently from 2D structures, which are rather pinned on the surface. It seems that 2D structures have some difference depending on the distribution of surface Si dangling bonds. We will give the details of the result of FPMD simulations in the presentation. [1] https://azuma.nims.go.jp [Preview Abstract] |
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T1.00099: Evolution of the Valley Position in Bulk Transition-Metal Chalcogenides and their Mono-Layer Limit Y.L. Chen, H.T. Yuan, Z.K. Liu, G. Xu, B. Zhou, S.F. Wu, D. Dumcenco, K. Yan, Y. Zhang, S.-K. Mo, P. Dudin, V. Kandyba, M. Yablonskikh, A. Barinov, Z.X. Shen, S.C. Zhang, Y.S. Huang, X.D. Xu, Z. Hussain, H. Y. Hwang, Y. Cui Layered transitionmetal chalcogenides have heavy elements with strong spin-orbit interaction, thus provide a unique way to extend functionalities of novel spintronics and valleytronics devices. Currently, most understanding of electronic bands near valleys is based on either theoretical calculations or optical measurements, leaving the detailed band structure elusive. In this talk, using angle-resolved photoemission spectroscopy with sub-micron spatial resolution, we systematically imaged the band structures and evolution across representative chalcogenides MoS$_{\mathrm{2}}$, WS$_{\mathrm{2}}$ and WSe$_{\mathrm{2}}$, as well as the thickness dependent from bulk to the monolayer limit. These results establish a solid basis to understand the underlying valley physics of these materials, and also provide a link between their electronic structures and physical properties for potential applications. [Preview Abstract] |
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T1.00100: Molybdenum disulfide grown by gas-phase precursor hydrogen sulfide in MOCVD Zihan Yao, Sunphil Kim, Arend Van der Zande, Wenjuan Zhu In this work, we demonstrate molybdenum disulfide (MoS$_{\mathrm{2}})$ growth using a new gas-phase precursor hydrogen sulfide in a metal-organic chemical vapor deposition (MOCVD) system, where the flow rate and partial pressure of the gas-phase hydrogen sulfide can be precisely controlled and the gas precursors can be evenly distributed in the growth chamber. The Raman and photoluminescence spectra of the synthesized MOCVD MoS$_{\mathrm{2}}$ indicate that the film is monolayer. We also systematically investigate the impact of the growth conditions on the morphology of the MoS$_{\mathrm{2}}$ grown by CVD using solid sulfur powder and by MOCVD using hydrogen sulfide. In CVD MoS$_{\mathrm{2}}$, the grain size and the layer thickness of CVD MoS$_{\mathrm{2}}$ increase as the carrier gas flow rate and growth time increase. In MOCVD MoS$_{\mathrm{2}}$, the shapes of the MoS$_{\mathrm{2}}$ grains are highly influenced by the flow rate of the gas precursor and the chamber pressure. This work is the first demonstration of MOCVD MoS$_{\mathrm{2}}$ growth using hydrogen sulfide gas precursor. This new technique can lead to large-scale uniform growth of MoS$_{\mathrm{2}}$ and provide a solid material foundation for future nanoelectronics. [Preview Abstract] |
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T1.00101: Characterization of Interface States in Black Phosphorus Capacitors with Various Gate Dielectrics Jialun Liu, Wenjuan Zhu Interfaces and gate dielectrics in two-dimensional (2D) materials-based electronic devices are critical for the performance. In this work, we systematically studied the interface between black phosphorus (BP) and gate dielectrics, including hexagonal boron nitride (hBN) and aluminum oxide (Al$_{\mathrm{2}}$O$_{\mathrm{3}})$, using capacitance and AC conductance methods measured at various temperatures. We found that the interface state density in BP/hBN capacitors is one order of magnitude lower than that in BP/ Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ capacitors, indicating superior quality of hBN crystals. In addition, we found that as the temperature decreases, the interface trap density extracted from ac conductance decreases due to the reduced trap emission/capture rate. For both BP/hBN and BP/ Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ capacitors, the capacitance--voltage (CV) characteristics show that the accumulation occurs when a positive bias is applied on the black phosphorus terminal, indicating that the black phosphorus is naturally p-type doped. This work systematically characterizes interface trap density in the black phosphorus capacitors and provides a new approach for monitoring the interface quality and improving the performance of 2D materials devices. [Preview Abstract] |
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T1.00102: Role of the interlayer coupling for the thermoelectric properties of CuSbS2 and CuSbSe2 Najebah Alsaleh, Nirpendra Singh, Udo Schwingenschlogl The electronic and transport properties of bulk and monolayer CuSbS$_2$ and CuSbSe$_2$ are determined using density functional theory and semi-classical Boltzmann transport theory, in order to investigate the role of the interlayer coupling for the thermoelectric properties. The calculated band gaps of the bulk compounds are in agreement with experiments and significantly higher than those of the monolayers, which thus show lower Seebeck coefficients. Since also the electrical conductivity is lower, the monolayers are characterised by lower power factors. Therefore, the interlayer coupling is found to be essential for the excellent thermoelectric response of CuSbS$_2$ and CuSbSe$_2$ even though it is of weak van der Waals type. [Preview Abstract] |
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T1.00103: Optical properties of large-area MoS2 thin films grown via magnetron sputtering: Thickness and substrate dependence Asma Alkabsh, Hassana Samassekou, Dipanjan Mazumdar Transition metal dichalcogenides (TMDS) have gained exceptional attention because of their thickness dependent electronic structure which makes them suitable for electronic and optoelectronic applications. MoS2 is among the most promising material in this family. Recently we have successfully developed growth of large-area MoS2 using magnetron sputtering. In this work, we investigated the large-area optical properties of few and bilayer MoS2 grown on different amorphous underlayers (BN and SiO2) using spectroscopic ellipsometry (SE), UV-VIS and Raman spectroscopy. SE spectra provided thickness and optical constants within 1.0-3.0 eV range, whereas broadband (0.5-6.5 eV) transmission and reflectance measurements provided direct measurements of optical constants through Glover-Tinkham analysis. A comprehensive analysis of thickness and substance dependence of optical properties of our large-area films will be presented and compared with existing literature reports and first-principles electronic structure. Also, Raman measurements reveal interesting disorder related effects on our MoS2 films. [Preview Abstract] |
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T1.00104: Relativistic space-charge-limited transport in Dirac semiconductor Yee Sin Ang, M. Zubair, L. K. Ang, Philippe Lavoie The theory of space-charge-limited (SCL) current was first formulated by Mott and Gurney more than 70 years ago based on the semiclassical transport of quasi-free electron in dielectric solids. Its validity for recently fabricated 2D materials, which can host different classes of exotic quasiparticles, remains questionable. Recently, SCL transport measurements in 2D Dirac semiconductor, such as MoS$_2$ and hBN monolayers, revealed anomalous current-voltage scaling of $J\propto V^{1.7}$ which cannot be satisfactorily explained by conventional theories. In this work, we propose a theory of space-charge-limited transport that takes into account the relativistic quasiparticle dynamics in 2D Dirac semiconductor based on semiclassical Boltzmann transport equation. Our relativistic SCL model reveals an unconventional scaling relation of $J\propto V^\alpha$ with $3/2<\alpha<2$ in the trap-free (or trap-filled) regime, which is in stark contrast to the Mott-Gurney relation of $\alpha=2$ and the Mark-Helfrich relation of $\alpha>2$. The $\alpha<2$ scaling is a unique manifestation of the massive Dirac quasiparticles and is supported by the experimental data of MoS$_2$. The relativistic SCL model proposed here shall provide a physical basis for the modelling of Dirac-material-based devices [Preview Abstract] |
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T1.00105: Electrical Properties of 2D Si$_{\mathrm{1-x}}$Ge$_{\mathrm{x}}$ alloys by ultra-fast thermal annealing C.H Lee, Q.Y. Chen, P.V. Wadekar, W.C. Hsieh, C.F. Chang, H.C. Huang, C.M. Shiau, Y.S. Hong, Y.P. Cheng, C.Y. Dang, P.C. Kung, Y.Y. Liang, S.H. Huang, Z.Y. Wu, C.M. Lin, S.T. Yu, L.W. Tu, N.J. Ho, H.W. Seo, W.K. Chu Ultra-fast thermal processing has been used to acquire 2D Si$_{\mathrm{1-x}}$Ge$_{\mathrm{x}}$ alloys of different x-values and effective thicknesses. X-ray reflectivity (XRR) data were analyzed with a three-layer model to obtain the thickness, roughness, mass density, and thus also the compositions. Comparison was then made with direct TEM imaging and SIMS depth profiling. The electrical properties according to the RT curves demonstrate semiconducting behaviors, as judged by their negative temperature coefficients, fit well with a functional of dual-energy Arrhenius relation representative of band conduction mechanisms. The extracted activation energies correspond to the mid-gap levels contributed by mutual alloying. The carrier concentrations, mobility and magnetoresistive behaviors will be discussed in relation to the material processing conditions for the 2D alloys. [Preview Abstract] |
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T1.00106: Investigating the Electronic and Structural Properties of Stanene Brendan Ferris, Antonio Cancio We investigate the structural and electronic properties of two-dimensional tin, or stanene, under compressive and tensile biaxial strain using density functional theory (DFT). Stanene possesses a buckled honeycomb-like structure and is a potential candidate for a quantum spin hall (QSH) insulator in which a quantum hall effect is generated in the absence of a magnetic field due to strong spin-orbit coupling (SOC). This effect, in combination with a strain-tunable band gap, makes stanene an interesting material for spintronic applications. Stanene is stable in both a high-buckled configuration which is metallic and a low-buckled configuration which gives rise to a QSH effect, and a transition between the two can be induced through strain. For a monolayer of tin, the high-buckled phase is more stable; we investigate whether multiple layers of tin or a combination of tin and germanium can ensure the low-buckled phase remains the most stable configuration. We use ABINIT, a plane-wave pseudopotential DFT code that accurately reproduces all-electron calculations of ground-state energies and densities, and which is used to determine the ground state atomic structure and electronic band structure. [Preview Abstract] |
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T1.00107: Near-Field Optical Study of 2D Semiconductors Shangjie Yu, Geng Li, Min Ouyang Two-dimensional semiconductors have been attractive recently due to their novel physical (e.g., optoelectronic, valleytronic and mechanical) properties in a single or few atomic layers. Scanning near-field optical microscopy (SNOM) provides an exciting avenue to study those novel 2D materials with high spatial resolution. For example, zero and one-dimensional features or physical processes, including local defects or domain boundaries, can be imaged, which provides unique physics insights. In this talk we will focus on a few progresses on exciton inhomogeneity mapping by near-field photoluminescence spectroscopy and microscopy. [Preview Abstract] |
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T1.00108: Molecular sensitivity on graphene decorated with noble metal nanoparticles: Graphene-mediated surface-enhanced Raman scattering (G-SERS) substrates Sanju Gupta, Alexander Banaszak, Tyler Smith Raman scattering signal enhancement that uses graphene as support, graphene-enhanced Raman scattering (G-SERS), is a recent phenomenon. While SERS enhancement arises due to electromagnetic mechanism, G-SERS also relies on chemical mechanism and therefore it shows unique molecular sensitivity. In this work, we developed graphene materials decorated with silver and gold nanoparticles for detecting methylene blue (MB) and rhodamine 6G (Rh6G) in view of optical and biological importance. The results illustrate that silver and gold nanoparticles immobilized on multilayer graphene graphene oxide and reduced graphene oxide significantly enhance the signal, and as cascaded amplification of SERS signal on multilayer architecture, larger than those only on metal nanoparticles. The sensitivity can be tuned by controlling the size of nanoparticles and the highest SERS enhancement factor (four orders) is achieved at optimal 30 nm silver and 40 nm gold nanoparticles on reduced graphene oxide and multilayer graphene. They serve as `smart' SERS platforms capable of detecting MB and Rh6G below 10 pM concentration. The enhancement is discussed in 1. molecular structures (molecular symmetry; face-down and edge-on) 2. charge-transfer interaction between molecules and graphene and 3. graphene-metal nanoparticle interfacial hybridization. The signal enhancement is supported by change in UV--vis absorption spectra of molecules in contact with graphene guiding molecular detection and biotechnology. [Preview Abstract] |
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T1.00109: Graphene oxide based contacts as probes of biomedical signals N. G. Hallfors, A. Devarajan, I. A. H. Farhat, A. Abdurahman, K. Liao, D. L. Gater, M. I. Elnaggar, A. F. Isakovic We have developed a series of graphene oxide (GO$_{\mathrm{x}})$ on polymer contacts and have demonstrated these to be useful for collection of standard biomedically relevant signals, such as electrocardiogram (ECG). The process is wet solution-based and allows for control and tuning of the basic physical parameters of GO$_{\mathrm{x}}$, such as electrical and optical properties, simply by choosing the number of GO$_{\mathrm{x}}$ layers. Our GO$_{\mathrm{x}}$ characterization measurements show spectral (FTIR, XPS, IR absorbance) features most relevant to such performance, and point towards the likely explanations about the mechanisms for controlling the physical properties relevant for the contact performance. Structural (X-ray topography) and surface characterization (AFM, SEM) indicates to what degree these contacts can be considered homogeneous and therefore provide information on yield and repeatability. We compare the ECG signals recorded by standard commercial probes (Ag/AgCl) and GO$_{\mathrm{x}}$ probes, displaying minor differences the solution to which may lead to a whole new way we perform ECG data collection, including wearable electronics and IoT friendly ECG monitoring. [Preview Abstract] |
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T1.00110: Characterizations of Ion Gel Dielectrics for Flexible Nanoelectronic Devices Kwanbyung Chae, Woongbin Yim, Van Tu Nguyen, Jaewoo Park, Ji-Yong Park Electric double layer transistor (EDLT) utilizing ion liquid can be operated with small voltages with large carrier density controllability. However, ion liquid is generally incompatible with various processes or operating environments of nanoelectronic devices. Ion gels prepared by mixing a host polymer and ionic liquid are good candidates for device applications overcoming the aforementioned shortcomings of ion liquid. In this study, we investigated ion gels consisting of PVDF-HFP (Poly(vinylidene fluoride-co-hexafluoropropylene)) and [EMIM][TFSI] (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) for device applications, especially for graphene field effect transistors (GFETs). Ion gels with different ratio of the host polymer and ionic liquid are prepared and their capacitance and conductance are measured to assess the optimal condition for device applications. The time response and stability of GFETs with ion gels are also investigated for possible flexible electronics applications. [Preview Abstract] |
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T1.00111: Large Area CVD MoS2 RF transistors with GHz performance Maruthi Nagavalli Yogeesh, Atresh Sanne, Saungeun Park, Deji Akinwade, Sanjay Banerjee Molybdenum disulfide (MoS$_{\mathrm{2}})$ is a 2D semiconductor in the family of transition metal dichalcogenides (TMDs). Its single layer direct bandgap of \textasciitilde 1.8 eV allows for high I$_{\mathrm{ON}}$/I$_{\mathrm{OFF}}$ metal-oxide semiconducting field-effect transistors (FETs). More relevant for radio frequency (RF) wireless applications, theoretical studies predict MoS$_{\mathrm{2}}$ to have saturation velocities, $v_{\mathrm{sat}}$ \textgreater 3\texttimes 10$^{\mathrm{6}}$ cm/s. Facilitated by cm-scale CVD MoS$_{\mathrm{2}}$, here we design and fabricate both top-gated and embedded gate short channel MoS$_{\mathrm{2}}$ RF transistors, and provide a systematic comparison of channel length scaling, extrinsic doping from oxygen-deficient dielectrics, and a gate-first gate-last process flow. The intrinsic $f_{\mathrm{T}}$ ($f_{\mathrm{max}})$ obtained from the embedded gate transistors shows 3X (2X) improvement over top-gated CVD MoS$_{\mathrm{2}}$ RF FETs, and the largest high-field saturation velocity, $v_{\mathrm{sat}} \quad =$ 1.88 \texttimes 10$^{\mathrm{6}}$ cm/s, in MoS$_{\mathrm{2}}$ reported so far. The gate-first approach, offers enhancement mode operation, I$_{\mathrm{ON}}$/I$_{\mathrm{OFF}}$ ratio of 10$^{\mathrm{8}}_{\mathrm{,}}$ and the highest reported transconductance (g$_{\mathrm{m}})$ of 70 $\mu $S/$\mu $m. By manipulating the interfacial oxygen vacancies in atomic layer deposited (ALD) HfO$_{\mathrm{2-x}}$ we are able to achieve 2X current density over stoichiometric Al$_{\mathrm{2}}$O$_{\mathrm{3}}$. We demonstrate a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS$_{\mathrm{2}}$ may be suitable for industrial-scale electronic applications. [Preview Abstract] |
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T1.00112: Silicene Catalyzed Reduction of Nitrobenzene to Aniline: a Computational Study Christopher Morrissey, Haiying He The reduction of nitrobenzene to aniline has a broad range of applications in the production of rubbers, dyes, agrochemicals, and pharmaceuticals. Currently, use of metal catalysts is the most popular method of performing this reaction on a large scale. These metal catalysts usually require high-temperature and/or high-pressure reaction conditions, and produce hazardous chemicals. This has led to a call for more environmentally friendly nonmetal catalysts. Recent studies suggest that silicene, the recently discovered silicon counterpart of graphene, could potentially work as a nonmetal catalyst due to its unique electronic property and strong interactions with molecules containing nitrogen and oxygen. In this computational study, we have investigated the plausibility of using silicene as a catalyst for the reduction of nitrobenzene. Possible reaction mechanisms will be discussed with a highlight of the difference between silicene and metal catalysts. . All calculations were performed in the framework of density functional theory. [Preview Abstract] |
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T1.00113: Inscribing rewriteable graphene pn junctions under ambient conditions Eberth Quezada, John Davenport, Hechin Chen, Kenji Watanabe, Takashi Taniguchi, Jairo Velasco Heterostructures of graphene and hexagonal boron nitride (BN) are highly tunable platforms that enable the study of novel physical phenomena and technologically promising nanoelectronic devices. Recently, for such graphene/BN heterostructures, it has been shown that electric field excitation can be used to control charge-defect ensembles in the underlying BN. This enables nanoscale control of rewriteable graphene pn junctions. Notably, the fabrication of these pn junctions requires highly specialized conditions, such as ultra-high vacuum and cryogenic temperatures, thus limiting further exploration of these pn junctions. To address this issue, we have developed a new technique that uses an ambient atomic force microscope to inscribe rewriteable graphene pn junctions. We will discuss our latest experimental progress on the development of this technique. [Preview Abstract] |
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T1.00114: Transport studies in graphene p-n junctions with Moiré superlattices Jiuning Hu, Ji Ung Lee, Hsin-Yen Lee, Albert Rigosi, Yanfei Yang, Chieh-I Liu, Randolph Elmquist, David Newell Graphene p-n junctions can offer unique opportunities for applications such as scalable quantum Hall resistance standards, electron optics and photon detection. In order to study transport properties across the p-n junction, van der Waals assembly technique is employed to fabricate graphene p-n junction samples. Boron nitride (BN)-graphene-BN sandwich heterostuctures are placed on substrates with thin (18 nm) silicon nitride dielectrics and buried tungsten gates (in plane gate separation is $\sim$ 50 – 150 nm). One of the BN layer is carefully aligned with graphene to produce Moiré pattern superlattices of wave length about 10 nm. Multiple satellite peaks are observed in the cross junction resistivity vs. gates voltages. Transport results (particularly across the p-n junction) in high magnetic field will be presented. Numerical simulation of transport based on tight-biding models will be provided to investigate the effect of the p-n junction interface. [Preview Abstract] |
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T1.00115: Investigating the Structure and Mechanical Properties of Graphene via Nanoindentation and Atomic Force Microscopy Alem Teklu, Canyon Barry, Matthew Palumbo, Collin Weiwadel, Narayanan Kuthirummal Graphene oxide was converted to multi-layer graphene via Lightscribe DVD burner reduction. Images of the samples were captured using the Nanosurf Flex AFM. Spectroscopic analysis via nanoindentation was performed on the samples after each oxygen reduction cycle, thus allowing for a comparison of stiffness, hardness, and the reduced Young's modulus based on the number of reduction cycles. The highest values obtained were after the fifth and final reduction cycle, yielding a stiffness of 109.64 \textpm 2.59 N/m, a hardness of 607.82 \textpm 10.33 GPa, and a reduced Young's modulus of 9.14 \textpm 0.21 GPa. This data was then compared to the values measured with a commercially purchased chemical - vapor deposited (CVD) graphene. The stiffness, hardness, and reduced Young's modulus for the commercial sample were 141.57 \textpm 2.14 N/m, 637.38 \textpm 6.09 GPa, and 11.80 \textpm 0.18 GPa, respectively. Parallel plate square capacitors (2.5 cm \texttimes 2.5 cm) were also built using these laser-scribed graphene samples. [Preview Abstract] |
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T1.00116: Ferroelectric memory based on molybdenum disulfide and ferroelectric hafnium oxide Wui Chung Yap, Hao Jiang, Qiangfei Xia, Wenjuan Zhu Recently, ferroelectric hafnium oxide (HfO$_{\mathrm{2}})$ was discovered as a new type of ferroelectric material with the advantages of high coercive field, excellent scalability (down to 2.5 nm), and good compatibility with CMOS processing. In this work, we demonstrate, for the first time, 2D ferroelectric memories with molybdenum disulfide (MoS$_{\mathrm{2}})$ as the channel material and aluminum doped HfO$_{\mathrm{2}}$ as the ferroelectric gate dielectric. A 16 nm thick layer of HfO$_{\mathrm{2}}$, doped with 5.26{\%} aluminum, was deposited via atomic layer deposition (ALD), then subjected to rapid thermal annealing (RTA) at 1000 \textdegree C, and the polarization-voltage characteristics of the resulting metal-ferroelectric-metal (MFM) capacitors were measured, showing a remnant polarization of \textasciitilde 0.6 $\mu $C/cm$^{\mathrm{2}}$. Ferroelectric memories with embedded ferroelectric hafnium oxide stacks and monolayer MoS$_{\mathrm{2}}$ were fabricated. The transfer characteristics after program and erase pulses revealed a clear ferroelectric memory window. In addition, endurance (up to 10,000 cycles) of the devices were tested and effects associated with ferroelectric materials, such as the wake-up effect and polarization fatigue, were observed. This research can potentially lead to advances of 2D materials in low-power logic and memory applications. [Preview Abstract] |
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T1.00117: Gate Tunable Magneto-resistance of ultra-thin WTe$_{\mathrm{2}}$ devices Jian-Hao Chen, Xin Liu, Chao-Yi Cai, Zhiran Zhang, Shibing Tian, Hong Lu, Shuang Jia, Takashi Taniguchi, Kenji Watanabe We have carried out magneto-transport experiment on ultra-thin WTe$_{\mathrm{2}}$ field effect transistors that are far away from charge neutrality (in the heavily electron-doped regime). We found that the magnetoresistance (MR) of the samples is tunable by gate voltage, and the two-fluid model captured most of the physics in this regime phenomenogically. By tuning the 2D electron-hole imbalance from 8.2 × 10$^{\mathrm{17}}$m-2 to 3.3 × 10$^{\mathrm{17}}$m$^{\mathrm{-2}}$, we were able to change the MR of the devices by 850{\%}. The change of MR could be as large as 400,000{\%} if the sample is tuned to neutrality when preserving the mobility observed in bulk samples. We also found that the change of MR of the ultra-thin WTe$_{\mathrm{2}}$ is determined largely by a single parameter, namely, the difference between the number of electrons and holes. Our findings show the potential of ultra-thin WTe$_{\mathrm{2}}$ as a variable magnetoresistance material in future applications such as magnetic field sensors, information storage and extraction, and galvanic isolators. [Preview Abstract] |
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T1.00118: Superconducting transition temperature of a boron nitride layer with a high niobium coverage. Gerardo Vazquez, Fernando Magana We explore the possibility of inducing superconductivity in a Boron Nitride (BN) sheet, by doping its surface with Nb atoms sitting on the center of the hexagons. We used first-principles density functional theory in the general gradient approximation. The Quantum-Espresso package [1] was used with norm conserving pseudo potentials. The structure considered was relaxed to their minimum energy configuration. Phonon frequencies were calculated using the linear-response technique on several phonon wave-vector meshes. The electron-phonon coupling parameter was calculated for a number of k meshes. The superconducting critical temperature was estimated using the Allen-Dynes formula with $\mu $* $=$ 0.1 - 0.15. We note that Nb is a good candidate material to show a superconductor transition for the BN-metal system. [1] Giannozzi P, Baroni S, Bonini N, Calandra M, Car R, Cavazzoni C, \textit{et al.} Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials. J Phys Condens Matter 2009; 21\textbf{: }395502-19. [Preview Abstract] |
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T1.00119: Development and Measurement of Carbon Nanotube-metal composite conductors Mike Sumption There is a significant opportunity for the development of CNT-metal composites with high electrical and thermal conductivity, as well as high current density. Such conductors, aiming at high conductivity and/or high conductivity per unit weight, have potential applications in electronics, transportation, and high power density applications. In this work, we discuss the development of CNT/metal composites based on powder in tube, electrochemical metallization, and co-deposition approaches. Our composites are formed with Cu and Al metals, and various CNT and graphene additions. Functionalization both during and after composite fabrication are discussed. A particularly promising approach appears to be the encapsulation and functionalization of CNT yarns. We have measured both electrical and thermal conductivity in the temperature range from room temperature to 400C, as well as conductor ampacity. Absolute as well as mass-normalized electrical and thermal conductivity results are discussed, and it is seen that results on a mass based basis are already of potential application interest for some composites. [Preview Abstract] |
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T1.00120: Non-covalent functionalization of carbon nanotubes: Controlling Chirality Selectivity via Alkyl Groups of Conjugated Co-Polymers Braden Weight, Brendan Gifford, Svetlana Kilina Carbon nanotubes (CNTs) play an important role in nanotechnology, including electronics, chemical sensors, and solar cells. Their electronic and optical properties depend on the size and geometry (chirality) of the nanotube. However, one main concern regarding nanotube application in optoelectronic devices is the difficulty of separating them based upon chirality after synthesis, as all known synthesis methods produce more than one chirality simultaneously. To get around this, one method is the functionalization of the CNTs via non-covalent bonding of co-polymers by wrapping them around the tube. We use force field simulations to explore the effects of various structural manipulations to the co-polymer 9,9-dialkylfluorenyl-2,7-diyl bipyridine (PFO-BPY) to find the preferential mechanisms of selective interactions between the PFO-BPY and CNTs of various chiralities. In particular, we focus on the effect of the branching in alkyl side-groups of PFO-BPY on their binding to the CNT surface. We have observed correlations between the side-group structures and their wrapping morphology on the CNT-Polymer interactions. Our calculations demonstrate that the branching in the position closest to the conjugated backboned results in the strongest interaction with all CNT. [Preview Abstract] |
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T1.00121: Evolution of Raman active mode in linear acetylenic Carbon chains. Aldo Raeliarijaona, Jorge Alarcon Ochoa, Humberto Terrones, Yung Joon Jung We investigate the Raman signatures of linear Carbon chains using first-principles calculations, namely Density Functional Theory, Density Functional Perturbation Theory as well as molecular dynamics techniques. Our studies of the linear acetylenic Carbon chains (CnH2) of varying lengths (n$=$2 to n$=$60) focus on: a) the identification of the Longitudinal Optic (LO) mode by using its phonon eigenvector and eigenvalue for each Carbon chain length, b) tracking the evolution of the LO mode in question with respect to chain length. Our analyses reveal that: 1. the LO modes tend to soften with increasing chain length, 2. the vibration signal of unstrained acetylenic Carbon chain of length n$=$24 matches well that of the Coalescence Inducing Mode (1850 cm-1) of Carbon nanotubes, 3. short acetylenic chains may also be responsible for the CIM Raman signal but require tensile strain to soften their vibration further, 4. as the acetylenic Carbon chain grow longer, higher harmonics (2nd or 3rd ) LO vibrations can be present and for longer chains these higher harmonics mode exhibit Raman signals close to the CIM value of 1850 cm-1. [Preview Abstract] |
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T1.00122: Computational studies of layered trititanates with magnetic doping Caleb Heath, Salvador Barraza-Lopez, Z Ryan Tian Layered titanate nanostructures are of great interest due to their ease of synthesis, modifiability, and variety in application. A profusion of experimental literature exists for these compounds but existing computational work has been limited in both quantity and scope. We examine hydrogen trititanate (H$_{2}$Ti$_{3}$O$_{7}$) with and without magnetic substitutional doping. Band structure, elastic properties, material stability, and magnetic properties of these titanates will be discussed. [Preview Abstract] |
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T1.00123: Graphene and Graphene Derivatives for Pharmaceutical Residual Removal from Drinking Water Ming Yu, Haifeng Zhang Strategy to keeping pharmaceuticals out of the nation's water supplies is the most essential and long-term procedure, while improving effective filtering systems at water treatment plants or at resident home is more practical and efficient. Current techniques including oxidation/ozonation, activated carbons, and filtration using membranes are relatively efficient when the concentration of pharmaceutical residues in the aquatic ecosystem is high, while when the concentration is relatively low, no one effective technique can remove so many different pharmaceuticals. To overcome such significant limitation, we are seeking to develop graphene based materials for pharmaceutical residual removal from drinking water and to initiate the study on dealing with this issue through fundamental understanding. Our results have shown that the graphene/graphene derivate could possess high adsorption rate to pharmaceutical residues (e.g., estradiol), promising their potential applications for pharmaceutical contamination removal from drinking water. Detailed information about the activities of the graphene with a variety of biomolecules, the type of adsorptions, and the effects of the attached hydroxyl, epoxyl, and carboxyl functional groups will be presented in the Meeting. [Preview Abstract] |
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T1.00124: pysimm: A Python Package for Simulation of Molecular Systems Michael Fortunato, Coray Colina pysimm, short for python simulation interface for molecular modeling, is a python package designed to facilitate the structure generation and simulation of molecular systems through convenient and programmatic access to object-oriented representations of molecular system data. This poster presents core features of pysimm and design philosophies that highlight a generalized methodology for incorporation of third-party software packages through API interfaces. The integration with the LAMMPS simulation package is explained to demonstrate this methodology. pysimm began as a back-end python library that powered a cloud-based application on nanohub.org for amorphous polymer simulation. The extension from a specific application library to general purpose simulation interface is explained. Additionally, this poster highlights the rapid development of new applications to construct polymer chains capable of controlling chain morphology such as molecular weight distribution and monomer composition. [Preview Abstract] |
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T1.00125: Origin of Unusual Dependencies of LUMO Levels on Conjugation Length in Quinoidal Fused Oligosiloles Nana Misawa, Mikiya Fujii, Ryo Shintani, Tomohiro Tsuda, Kyoko Nozaki, Koichi Yamashita Quinoidal fused oligosiloles, a new family of silicon-bridged $\pi$-conjugated compounds, have been synthesized and their physical properties showed a unique trend in their LUMO levels, which become higher with longer $\pi$-conjugation.\footnote{Nozaki el.al, {\it JACS.} {\bf 2016}, {\it 138}, 3635} Although this trend was reproduced by the DFT calculations, its origin remained to be discussed. In this work we performed quantum chemical calculations and discovered that the unusual LUMO trend is attributable to the $\pi$-frameworks. We elucidated its origin by orbital correlation diagrams based on classical H\"{u}ckel calculations, essentially. However, LUMO trends cannot fully be explained only by H\"{u}ckel calculations because of the lack of the consideration of geometries. In the case of quinoidal fused oligosiloles, judging from DFT calculation results, the presence of silole fused structure play an important role in fixing the bond angles of the linear polyenes as an interior angle of siloles, leading to the unusual LUMO behavior. The qualitative but essential understanding of these LUMO trend would provide new insight into molecular design of $\pi$-conjugated compounds for tuning their LUMO levels. [Preview Abstract] |
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T1.00126: Crystalline inclusion, tensile strain and shear bands in metallic glass nanowires Matias Sepulveda-Macias, Nicolas Amigo, Gonzalo Gutierrez A molecular dynamics study of the effect of crystalline inclusions on the mechanical properties of metallic glass nanowires is presented. The system consists of a parallelepiped composed by a million atoms interacting by means of an embedded atom potential, where three different crystalline spheres of 2, 4 and 6 nm radii has been included. These systems have been submitted to uniaxial tensile test up to 25\% of strain. We describe in detail the evolution of the shear band formation confirming that it begin at the interface between the inclusion and glass phase, growing in the direction of the applied tensile force. In contrast to the case of bulk material, in nanowires the inclusion does not play a significant role on the mechanical properties of the sample. Nevertheless, the inclusion plays a role in developing an interconnected network of loosely packed atom regions, which defines a particular medium range order in the sample. [Preview Abstract] |
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T1.00127: Modeling the Local Structure of Amorphous Materials: A Density Functional Theory Investigation Kai Gong, Ongun Ozcelik, Claire White Here, we present an iterative methodology alternating between density functional theory (DFT) calculations and pair distribution function (PDF) analysis to uncover the detailed atomic structure of highly amorphous materials. In this methodology, the DFT calculations are used to maintain chemical feasibility of the atomic structure, while the experimentally-driven refinements allow for exploration of the potential energy landscape. Through this iterative process, a final structure is obtained that is not only thermodynamically favorable but also in agreement with experiment data. Previously, we have demonstrated the applicability of similar DFT-PDF iterative methods in metakaolin and amorphous magnesium carbonate. Here, we have modified the methodology and applied it to resolve the atomic structure of ground granulated blast-furnace slag, a highly disordered calcium-magnesium aluminosilicate glassy material. Prior to applying the iterative process, a high temperature molecular dynamics (MD) simulation was used to generate a reasonable starting structure, which was found to be crucial. The iterative methodology outlined here is expected to be readily transferable to other disordered material systems where detailed atomic structures are currently not available. [Preview Abstract] |
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T1.00128: Graphene Nanoribbons Encapsulated inside Boron Nitride Nanotubes. Hamid Reza Barzegar, Eduardo Gracia-Espino, Thang Pham, Alexandr V. Talyzin, Alex Zettl We report on bottom-up synthesis of graphene nanoribbons inside boron nitride nanotubes, using small molecules as building blocks. The small molecules are inserted in the inner cavity of the nanotube in vapor phase and further fused to each other at high temperature. The width of the synthesized nanoribbon is equal to the width of the used small molecule and can be tuned by tuning the width of the small molecules. We employ theoretical modeling and calculation to study the possible interaction between the synthesized graphene nanoribbons and boron nitride nanotube as well as electronic properties of the hybrid structure. The encapsulated carbon nanostructures can be eliminated from the inner cavity of the filled boron nitride nanotube via oxidation without any damage to the nanotube structure. [Preview Abstract] |
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T1.00129: Density Functional Calculation of Quantum Wire chin-sheng wu Quantum wire displays quantum ~effects on the electrical transport properties. If the diameter of a wire is in the nanometer dimension, the energy and momentum of free electrons will be limited to a series of discrete values. Following from the quantization of electron energy, the ~electrical conductance~ is found to be quantized in multiples of \textit{~2}$_{e}^{2}_{/\thinspace h}_{\mathrm{\thinspace }}$where e ~is the ~electron charge ~and ~h is the~ Planck constant. The conductance of a ballistic ~quantum channel is equal to the summation of each electron conductance. ~We apply density functional theory to calculate the electron structure of quantum wire. To perform a calculation for a specific case, we take Al ($r_{s\thinspace =}$\textit{2}) atoms for the quantum wire, which behave as potential quantum well with the barrier plus biased voltage between the two boundaries. The number of electrons is determined by the cross section and length of the quantum wire. The current density j is equal to electron charge density multiplying velocity. The quantizations of conductance ~corresponding to the lowest~ energy states ~are only observed for atom-size wires. Their corresponding wavelength being thus extremely small they have a very large energy separation which makes resistance quantization observable even at room temperature. [Preview Abstract] |
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T1.00130: Ultrafast strong broadband light source generated in nanoscale plasmonic Au-AAO-Al structures Junbo Han, Linhua Yao, Zongwei Ma we demonstrate an ultrafast strong broadband photoluminescence (PL) from Au-AAO-Al composite under low excitation power intensity of 3.8\textasciitilde 34.5 GW$/$cm2. The emission wavelength is in the range of 450-1050 nm and the lifetime is under sub-nanosecond. Comparative studies of PL in Au-AAO-Al with different Au rod length and Au-AAO without Al coupling layer, together with the finite difference time domain (FDTD) calculations, present that the fast PL originates from the surface plasmon enhanced supercontinuum generation (SCG) in AAO membrane. The observations indicate that strong SCG could be realized in nanoscale plasmonic structures, which have promise applications in the minimization and integration of ultrafast lighting sources in photonic devices. [Preview Abstract] |
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T1.00131: Increased sensitivity of amorphous carbon based gas-sensors due to different Au nanostructures. K. W. Liu, B. Y. Chen, H. S. Hsu, S. P. Ju, S. J. Sun, H. Chou We reported that gold nanoparticles attached with the amorphous carbon (a-C) could promote sp$^{\mathrm{2}}$ bonds around the gold nanoparticles. This can change the hopping characteristics and can control the carrier transport which results in increased conductivity. These nanocomposites exhibit a superior sensitivity towards NH$_{\mathrm{3}}$ at room temperature, as well as good reproducibility and short response/recovery time. To increase the sensitivity of gas-sensors we need to increase the interface effect between gold nanostructures and a-C. To increase this interface effect we choose gold nanorods instead of nanoparticles. To grow the gold nanorods along z-direction perpendicular to the substrate surface we use low temperature deposition technique. Improvement in the interfacial effect will greatly improve the sensitivity of gas-sensors. [Preview Abstract] |
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T1.00132: Charged impurity screening by monolayer graphene on a substrate at finite temperature Andrii Iurov, Godfrey Gumbs, Danhong Huang The static shielding of a charged impurity in the vicinity of a graphene layer on a substrate is investigated. Linear-response theory is employed for treating the interaction between the impurity, graphene layer and the thick conducting substrate. Our calculations involve a derivation of the inverse dielectric function which is obtained within the time-dependent self-consistent Hartree-Fock approximation. The cases we consider correspond to a gapped and gapless graphene and the effect of temperature on the static shielding. We also report on the effect on the shielding as the location of the nonmagnetic charged impurity is varied. [Preview Abstract] |
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T1.00133: Tight-binding calculation of single-band and generalized Wannier functions of graphene Allan Victor Ribeiro, Alexys Bruno-Alfonso Recent work has shown that a tight-binding approach associated with Wannier functions (WFs) provides an intuitive physical image of the electronic structure of graphene. Regarding the case of graphene, Marzari et al. [1] displayed the calculated WFs and presented a comparison between the Wannier-interpolated bands and the bands generated by using the density-functional code. Jung and MacDonald [2] provided a tight-binding model for the $\pi $-bands of graphene that involves maximally localized Wannier functions (MLWFs). The mixing of the bands yields better localized WFs [3]. In the present work, the MLWFs of graphene are calculated by combining the Quantum-ESPRESSO code and tight-binding approach. The MLWFs of graphene are calculated from the Bloch functions obtained through a tight binding approach that includes interactions and overlapping obtained by partially fitting the DFT bands. The phase of the Bloch functions of each band is appropriately chosen to produce MLWFs. The same thing applies to the coefficients of their linear combination in the generalized case. The method allows for an intuitive understanding of the maximally localized WFs of graphene and shows excellent agreement with the literature. Moreover, it provides accurate results at reduced computational cost. [1] N. Marzari, A. A. Mostofi, J. R. Yates, I. Souza, and D. Vanderbilt, Rev. Mod. Phys. 84, 1419 (2012). [2] J. Jung and A.H. MacDonald, Phys. Rev. B 87, 195450 (2013). [3] D.R. Nacbar and A. Bruno-Alfonso, Phys. Rev. B 85, 195127 (2012). [Preview Abstract] |
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T1.00134: Transport through Polyene Junctions in between Angled-cut Armchair Carbon Nanotubes Yiing-Rei Chen, Ming-Kuan Lin Single-polyene and two-polyene molecular junctions bridging carbon nanotube (CNT) leads are further studied in this work. We calculate and investigate the Green’s function of the CNT leads from the edge into the bulk tube, to show the oscillation in the layer-by-layer DOS of the cross-cut armchair CNT’s, and the edge states of the cross-cut zigzag CNT’s. Also exhibiting a zigzag rim at the cut, an angled-cut armchair CNT gives a layer-by-layer DOS that shows not only evanescent edge states, but also an oscillation into the bulk tube. We study the polyene junction transport with these angled-cut armchair CNT leads, to find the interference between transport channels. The contributions from the bulk states and edge states are differentiated, by understanding the difference in the Green’s functions obtained from direct integration method and iterative method, separately. [Preview Abstract] |
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T1.00135: Detailed line shape analysis of the C KVV Auger peak of two carbon allotropes measured using a time of flight positron annihilation induced Auger electron spectrometer A J Fairchild, V A Chirayath, M D Chrysler, R W Gladen, S K Imam, A R Koymen, A H Weiss We report a detailed line shape analysis of the positron induced C KVV Auger line shape from highly oriented pyrolytic graphite (HOPG) and a single layer of graphene grown on polycrystalline Cu. A model consisting of the self-fold of the one-electron density of states including terms for hole-hole interactions, charge screening effects, and intrinsic loss mechanisms is compared to experimental C KVV line shapes measured using a positron induced Auger electron spectrometer (PAES). In traditional Auger spectroscopies which use an electron or photon to initiate the Auger process, extracting the relatively small Auger signal from the large secondary background can be quite difficult. Using a very low energy positron beam to create the core hole through an anti-matter matter annihilation entirely eliminates this background. Additionally, PAES has sensitivity to the top most atomic layer since the positron becomes trapped in an image potential well at the surface before annihilation. Therefore, the PAES signal from a single layer of graphene on polycrystalline Cu is primarily from the graphene overlayer with small contributions from the Cu substrate while the PAES signal from HOPG can be viewed as a single graphene layer with a graphite substrate. The influence of these two substrates on C KVV line shape is discussed. [Preview Abstract] |
(Author Not Attending)
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T1.00136: Electron dynamical polarization function and plasmons in metallic armchair graphene nanoribbons Samvel Badalyan, Artsem Shylau, Francois Peeters, Antti-Pekka Jauho The dynamical polarization function and plasmon excitations in metallic armchair graphene nanoribbons are investigated using the random phase approximation. An exact analytical expression for the polarization function of Dirac fermions is obtained, valid for arbitrary temperature and doping. We find that at finite temperatures, due to the phase space redistribution among inter-band and intra-band electronic transitions in the conduction and valence bands, the full polarization function becomes independent of temperature and position of the chemical potential. It is shown that for a given width of nanoribbon there exists a single plasmon mode whose energy dispersion is determined by the graphene’s fine structure constant. In the case of two Coulomb-coupled nanoribbons, this plasmon splits into in-phase and out-of-phase plasmon modes with splitting energy determined by the inter-ribbon spacing. [Preview Abstract] |
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T1.00137: Strain-induced chiral symmetry breaking leads to Dirac cone opening in graphene heterostructure Enrique Munoz, Deya Das, Swastibrata Bhattacharyya, Abhishek Singh Using first-principles calculations, we report [1] a large band-gap opening in the van der Waals heterostructure of graphene and graphane (hydrogenated graphene) under normal compressive (NC) strain. In the presence of graphane, interlayer charge transfer from graphene to graphane triggers the intralayer charge redistribution in graphene, breaking the equivalence of the two sublattices. The application of the NC strain enhances the inter- and intralayer charge transfer leading to a splitting of the Dirac cone, reflected as a redshift of the G peak in Raman spectra. We further present an analytical theory, based on the Dirac approximation, that provides a simple explanation of this effect within a general framework that suggests the same mechanism for band gap opening can be observed in other graphene based heterostructures. References [1] D. Das, S. Bhattacharyya, E. Munoz and A. K. Singh, Phys. Rev. B 94, 115438 (2016) [Preview Abstract] |
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T1.00138: Combined effect of doping and temperature on the anisotropy of plasmon Antonios Balassis, Godfrey Gumbs, V. M. Silkin We compare the plasmon dispersion relations for monolayer graphene when the sample is doped with carriers in the conduction band and the temperature is zero versus when the temperature is finite and there is no doping. Additionally, we have obtained the plasmon excitations when there is doping at finite temperature. The plasmon dispersion in the $\Gamma M$ direction may be different in substantial ways from that along the $\Gamma K$ direction at sufficiently high temperature and doping concentrations. The results were obtained in the random-phase approximation which employs energy bands calculated using {\em ab initio\/} density functional theory. In addition to the usual square root plasmon dispersion relation, a linear (optical) plasmon mode may appear in the $\Gamma K$ but not the $\Gamma M$ direction. [Preview Abstract] |
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T1.00139: Influence of the Raman laser power on the opto-electronics properties in graphene with water molecule R R Rey-González, A. Champi, A. M. Rojas Cuervo The study of physical and chemical properties of nanostructures has contributed in great part with advance of the nanotechnology, which is important for the development of present and future technological applications. An important key in this purpose is the interaction of atoms and molecules with nanostructures. The principal interest of this experimental work is to study these processes on the interaction between liquid and vapor phases water with a graphene bilayer which is obtained through micromechanical exfoliation technique from a sample of natural graphite deposited on a $SiO_2$ substrate. The number of layers and the interaction water-bilayer are analyzed systematically by means of Raman spectroscopy $\lambda$ = 532nm). Also, the influence of variation of the Raman laser power and its effects in the opto-electronic properties of the system are studied. From the usual G, D and 2D bands of these spectra, we analyze the relation between the laser power and some band parameters, such as its area, position and wide. Finally, these results permit us to quantify the density of defects and the distance among them as function of Raman power before and after of the water vapor incorporation in bilayers [Preview Abstract] |
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T1.00140: Stacking effects on bilayer graphene and dichalcogenide hybrid structures Abdulrhman Alsharari, Mahmoud Asmar, Sergio Ulloa Heterostructures of graphene (G) and transition metal dichalcogenides (T) create novel 2D systems with exotic properties[1]. In multilayers, stacking ordering is crucial to the resulting band structure in such systems. We use a tight binding formalism to calculate the band structure and analyze it in terms of the symmetries of the Hamiltonian. We characterize state topology through the calculation of Berry curvatures, and Chern numbers, and study zigzag edge states to identify and classify different phases. A superstructure of G-G-T is shown to exhibit a massive Dirac band structure at low energy similar to the TMDs band structure with scaled parameters. A possible inverted mass gap regime appears upon changing Rashba spin orbit coupling strength. A second G-T-G superstructure preserves mirror symmetry (z to -z) which leads to the formation of bands with definite parity 1(-1) that do not interact with each other. These two sets of bands have inverted and parabolic band structure, respectively. Possible symmetry breaking effects, e.g., mirror symmetry breaking in the presence of a field, may lead to distinct topological phases in the system. [1] A. M. Alsharari et al., arXiv:1608.00992. [Preview Abstract] |
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T1.00141: Inhomogeneous ozone doping and heat induced defects in graphene studied by infrared near-field microscopy Wenjie Wang, Jiawei Zhang, Haiming Deng, Megnkun Liu, Du Xu With the potential use of surface plasmon such as transfer data many orders faster than traditional wires, it has been very popular in research. The fact is that the wavelength of of plasmon is much shorter than the one of free space radiation. The UV ozone doping level can be fine controlled in room temperature creating selected plasmon circuit. We study inhomogeneous graphene plasmonics in ozone doped graphene using scattering-type scanning near-field infrared microscopy and spectroscopy. The single layer and bilayer graphene are doped with different dosage of ozone under UV exposure, which lead to surface inhomogeneity and inhomogeneous graphene plasmon polarition excitation under tip. After annealing the ozone doped graphene in air, the inhomogeneous doping induced plasmons disappear, together with the occurrence of local defects after high temperature annealing. [Preview Abstract] |
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T1.00142: Adiabatic Quantum State Transfer in Triple Quantum Dot System in Monolayer Graphene Sankalpa Ghosh, Amit Vashisht, Akash Kumar Singh, Rohit Narula We describe a scheme for the adiabatic population transfer of electron between two graphene quantum dots (GQDs) spatially separated by a potential barrier between them in a triple-dot system via the dark state. We give a comparison of results between existing semiconductor quantum dot systems for instance GaAs. We plan to extend our analysis to multiple GQDs which should then work as an effective quantum information processing unit. [Preview Abstract] |
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T1.00143: Plasmonics for Asymmetric Encapsulation of Graphene Paula Fekete, Godfrey Gumbs, Dipendra Dahal We have established a self-consistent theory for calculating the plasmon dispersion relation for an encapsulated graphene monolayer that is sandwiched between two conductors which are distinctively different. The thick conductors are characterized by their bulk plasmon frequency and their surfaces are separated by a distance $d$. We present numerical results for the plasmons which are not Landau damped. We also derived analytic results for these collective modes in the long wavelength limit and demonstrate that the lowest-lying branch has a square root dependence on $d$ and obeys a linear law for the in-plane wave vector. The two higher frequency modes have dispersion relations which originate at the surface plasmon frequencies of the semi-infinite conductors and in the long wavelength limit the lowest-order corrections are proportional to the square of the in-plane wave vector. [Preview Abstract] |
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T1.00144: Atomic hydrogen induced resonant scattering in bilayer graphene Tiancong Zhu, Jyoti Katoch, Denis Kochan, Simranjeet Singh, Jaroslav Fabian, Roland Kawakami Adatom decoration of the graphene surface is a powerful technique to engineer both its charge and spin related properties. In particular hydrogenation of graphene is interesting due to the possibility of inducing spin orbit coupling, and magnetic moment as well as opening a band gap. Moreover theory also predicts ferromagnetic ordering when hydrogen is adsorbed on the same sublattice. We performed in-situ charge transport study of bilayer graphene devices as a function of successive controlled amount of atomic hydrogen in ultra-high vacuum chamber at low temperatures (20 K). Atomic hydrogen is generated by a thermal gas cracker, and gate dependent resistance of graphene is measured after each atomic hydrogen exposure. On hydrogenation, we observed two additional resistance peaks appear on the electron side of the gate dependent resistance curve. Through DFT calculation and tight binding model, we attribute these two peaks to resonant scattering from hydrogen atoms adsorbed on different sublattices of bilayer graphene. Furthermore, we will discuss the annealing study of the hydrogenated bilayer graphene devices, which indicates the possibility to achieve sublattice selective hydrogenation. [Preview Abstract] |
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T1.00145: Temperature-dependent collective effects for silicene and germanene Godfrey Gumbs, Andrii Iurov, Danhong Huang We calculated the exchange and correlation energies as well as the dynamical polarization functions for silicene, germanene and other buckled honeycomb lattices for a variety of temperatures. Comparison is made for the dependence of these energies on the chemical potential, field-induced band gap and the temperature from which we concluded that in many cases they behave qualitatively similarly. For example, increasing the doping or varying the temperature. In our calculations, we used the dynamical polarizability to investigate the ``split'' plasmon branches in buckled lattices and predict unique splitting, which is different from that in gapped graphene, for various energy gaps. Our results are crucial for stimulating electronic, transport and collective particle studies of these materials, as well as for enhancing silicene-based fabrication and technologies for photovoltaics and transistor devices. [Preview Abstract] |
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T1.00146: Landau quantization in monolayer GaAs Hsien-Ching Chung, Ching-Hong Ho, Cheng-Peng Chang, Chun-Nan Chen, Chih-Wei Chiu, Ming-Fa Lin In the past decade, the discovery of graphene has opened the possibility of two-dimensional materials both in fundamental researches and technological applications. However, the gapless feature shrinks the applications of pristine graphene. Recently, researchers have new challenges and opportunities for post-graphene two-dimensional nanomaterials, such as silicene (Si), germanene (Ge), and tinene (Sn), due to the large enough energy gap (of the size comparable to the thermal energy at room temperature). Apart from the graphene analogs of group IV elements, the buckled honeycomb lattices of the binary compositions of group III-V elements have been proposed as a new class of post-graphene two-dimensional nanomaterials. In this study, the generalized tight-binding model considering the spin-orbital coupling is used to investigate the essential properties of monolayer GaAs. The Landau quantization, band structure, wave function, and density of states are discussed in detail. [Preview Abstract] |
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T1.00147: Thickness dependence of Electron Energy Loss Spectra (EELS) of MoS2 films Feng Xue, Xinxu Yan, Zhe Wang, Hui Wang, Xiaoqing Pan, Ruqian Wu Band structures and optical properties of monolayer, bilayer, and bulk MoS2 are studied using the GW approximation in conjunction with the Bethe-Salpeter equation (BSE). The calculated electron energy loss spectra (EELS) of these systems show peak structures that depend on the thickness. In particular, the pronounced peak near 3 eV moves to lower energy with the increasing of film thickness. Through analysis of transition matrices and density of states, we attribute this peak shift to modifications of the band structures through the weak interlayer van der Waals interaction. Comparison between theory and experiment are made to reveal the physical insights and to provide guidance for the utilization of novel two-dimensional materials. [Preview Abstract] |
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T1.00148: Effect of vacancy in penta-graphene nanoribbons: A first principals study Khaldoun Tarawneh, Renat Sabirianov Penta-graphene has been proposed recently as a new stable carbon allotrope which is mechanically stronger than graphene. To future explore its properties, we use the first-principals calculations to reveal that the electronic properties of penta-graphene nanoribbons can be modified in the presence of vacancy defect. Our calculations showed that the band gap of penta-graphene nanoribbons changes with changing the width of the ribbons and on the position of the vacancy relative to its edge. The vacancy formation energy is calculated to be 8.42 eV in the middle of the ribbons and decreases to 6.8 eV when the vacancy position is close to the edge of the ribbon. These results for a stable nanoribbon with a large band gap is promising for designing optoelectronic devices. [Preview Abstract] |
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T1.00149: Valley-dependent transport through quantum barriers in bilayer graphene. Bing-Chen Huang, Feng-Wu Chen, Yu-Shu Wu Valley-based quantum devices are made possible in graphene due to the existence of an inherent carrier degree of freedom - valley pseudospin. As shown previously, a valley contrast emerges when obliquely incident electrons are transmitted through lateral graphene structures with a single interface where discontinuity of bandgaps or potentials occurs [1]. In this presentation, we expand the study to graphene structures with multiple interfaces, especially those with quantum barriers, and investigate the intriguing behavior of valley polarization in such structures. We focus on the Bernal-stacking bilayer graphene with broken inversion symmetry. Numerical results for single and double quantum barrier systems are presented. We apply the tight-binding model of graphene lattice, impose on the electron state the current continuity condition at each interface, solve for the wave function and then calculate the electron transmission. Our findings show that in the case of single barrier structures the valley polarization is positively correlated to the barrier width. In the case of double barrier structures, carrier transport through resonant tunneling states can lead to high valley polarization. Overall, transmission of obliquely incident electrons through single or double quantum barriers offers an effective way to generate valley-polarized electron sources. [1]F.W. Chen, M.Y. Chou, Y.R. Chen, and Y.S. Wu. Phys. Rev. B 94, 075407 (2016) [Preview Abstract] |
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T1.00150: Raman and transport studies of V2O5 thin flakes Gaihua Ye, Sukrit Sucharitakul, Zhipeng Ye, Xuan Gao, Rui He Vanadium pentoxide, V2O5, is layered material. It is used in many industrial chemical reactions. For bulk V2O5, the lattice parameters are a=11.51 (angstrom), b=3.56 (angstrom), and c=4.37 (angstrom). We probed vibrational and electrical properties of exfoliated flakes of V2O5 with thicknesses between 10-100 nm using Raman spectroscopy and electrical transport. We find that V2O5 is highly anisotropic in the plane. Intensities of Raman modes depend strongly on the relative orientation between the crystal axes and the directions of polarization of incident/scattered light. Through four-probe measurement, conductance anisotropy up to order of 102 between a and b crystal axis is observed. Moreover, samples show thermally activated carriers with activation energy extracted to be 0.11-0.14 eV through electrical conductance measurement at different temperatures. Through Hall measurement, the exfoliated samples show Hall mobility up to 7 cm2/Vs comparable to that of bulk crystals. [Preview Abstract] |
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T1.00151: Optical states and tunable bandgaps for silicene, germanene and molybdenum disulfide Liubov Zhemchuzhna, Andrii Iurov, Godfrey Gumbs, Danhong Huang Closed-form analytical results are obtained for the energy dispersion and bandgaps when the electron states are dressed , i.e. the states which arise when an electron interacts with electromagnetic radiation having different polarizations. Our formalism applies to several recently discovered structures with gapped Dirac cones such as silicene, germanene, molybdenum disulfide and phosphorene. Each of these materials has a some type of symmetry breaking which is reflected in the energy band dispersions. Most importantly, we have found that the band gap may be either increased or decreased by adjusting the electron-photon interaction. [Preview Abstract] |
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T1.00152: Visualization of defect-induced excitonic properties of the edges and grain boundaries in synthesized monolayer molybdenum disulfide AKM Newaz, A.E. Yore, A. Miller, W. Crumrine, B. Redd, J.A. Tuck, Bin Wang, K.K.H Smithe, E. Pop Understanding nanoscale optical behavior of the edges and grain boundaries of synthetically grown transition metal dichalcogenides (TMDCs) is vital for optimizing their optoelectronic properties. Here we present our experimental work on spatial photoluminescence (PL) scanning of large size ($\geq 50 \mu$m) monolayer MoS$_2$ grown by chemical vapor deposition (CVD) using a diffraction limited blue laser beam spot (wavelength 405 nm) with a beam diameter as small as $\sim 200$ nm allowing us to probe nanoscale excitonic phenomena which was not observed before. We have found several important features: (i) there exists a sub-micron width strip ($\sim 500$ nm) along the edges that fluoresces $\sim 1000\%$ brighter than the region far inside; (ii) there is another brighter wide region consisting of parallel fluorescing lines ending at the corners of the zig-zag peripheral edges; (iii) there is a giant blue shifted A-excitonic peak, as large as $\sim 120$ meV, in the PL spectra from the edges. Using density functional theory calculations, we attribute this giant blue shift to the adsorption of oxygen dimers at the edges, which reduces the excitonic binding energy. Our results offer an attractive route to tailor optical properties at the TMDC edges through defect engineering. [Preview Abstract] |
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T1.00153: Second Harmonic Generation of Transition Metal Dichalcogenides from First-Principlies. Michael Lucking, Humberto Terrones The monolayers of transition metal dichalcogenides (TMDs) have been observed to have strong non-linear optical properties. We present calculations of the second harmonic generation (SHG) of nanostructured TMDs. In particular, the zigzag nanotubes exhibit a strong enhancement in the second harmonic signal. However, the armchair nanotubes have no second harmonic signal, making SHG an efficient tool for determining the chirality of grown nanotubes. [Preview Abstract] |
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T1.00154: Electronic transport close to semi-infinite 2D systems and their interfaces Fanbing Xia, Jian Wang Transport properties of 2D materials especially close to their boundary has received much attention after the successful fabrication of Graphene. While most previous work is devoted to the conventional lead-device-lead setup with a finite size center area, this project investigates real space transport properties of infinite and semi-infinite 2D systems under the framework of Non-equilibrium Green's function. The commonly used method of calculating Green's function by inverting matrices in the real space can be unstable in dealing with large systems as sometimes it gives non-converging result. By transforming from the real space to momentum space, the author managed to replace the matrix inverting process by Brillouin Zone integral which can be greatly simplified by the application of contour integral. Combining this methodology with Dyson equations, we are able to calculate transport properties of semi-infinite graphene close to its zigzag boundary and its combination with other material including s-wave superconductor. Interference pattern of transmitted and reflected electrons, Graphene lensing effects and difference between Specular Andreev reflection and normal Andreev reflection are verified. We also generalize how to apply this method to a broad range of 2D materials. [Preview Abstract] |
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T1.00155: Conductance and refraction across a Barrier in Phosphorene Dipendra Dahal, Godfrey Gumbs The transmission coefficient and ballistic conductance for monolayer black phosphorene is calculated when a potential step or square barrier is present. The Landauer-B¨uttiker formalism is employed in our calculations of the conductance. We obtain the refractive index for the step potential barrier when an incident beam of electron travel along different paths so as to observe what role the anisotropy of the energy bands plays. Numerical results are presented for various potential heights and barrier widths and these are compared with those for gapless and gapped graphene. [Preview Abstract] |
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T1.00156: Light enhancement due to Coulomb catalysis in hybrid Molybdenum Disulfide Yuba Poudel, Arup Neogi Bulk molybdenum disulfide (MoS$_{2})$ material has an indirect bandgap semiconductor and does not normally emit light. Reducing the thickness to a few monolayer modifies the bandstructure of MoS$_{2}$ to a direct bandgap and results in light emission. However, the light emission from a single monolayer is usually weak due to the relatively low absorption cross-section that a single monolayer provides. Thereby there has been efforts to use metal nanoparticles (NPs) for increasing the light emission efficiency of a single monolayer MoS$_{2}$ due to localized plasmon (LSP) interaction with excitons. The localized plasmons due to metal NPs when tuned to the emission energy of the MoS$_{2}$ exciton emission can increase the radiative recombination rate or hot carrier effects and lead to enhanced PL emission. However, the resonant interaction of emitted light with the LSP is dissipative. To avoid dissipative effects of metal nanoparticles, off-resonant LSP interaction due to metal is used for light enhancement. Electrostatic image charge effect has led to significant enhancement in GaN, GaAs, ZnO and graphene oxide system. In this work we demonstrate the PL enhancement from MoS$_{2}$ coupled to Ag NPs. The electrostatic basis of light enhancement is confirmed using time and temperature dependent PL measurements. [Preview Abstract] |
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T1.00157: Dislocation-mediated plasticity of tubular crystals Daniel Beller, David Nelson We study tubular crystals, two-dimensional lattices with cylindrical topology, in which the radius is not fixed; the geometry can deviate from that of a perfect cylinder, controlled by a combination of stretching and bending energies. Through computer simulation of discretized surfaces, supplemented by analytic calculations, we show how the local radius profile of the tube responds to the presence of dislocation defects. A shift in the tube’s radius accompanies the change in the tube’s phyllotactic indices along the cylinder axis, on either side of a dislocation, while the radius itself oscillates in the vicinity of the dislocations. When the ends of the tube are free, as opposed to periodic boundary conditions, dislocations can also significantly reorient the tube axis. Through this reorientation, dislocation pairs cause bent, zig-zagged, and intermediately deformed tube conformations, which are dynamically altered by helical glide motion of dislocations through the lattice in response to external stresses. [Preview Abstract] |
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T1.00158: Ultra-fast three-dimensional X-ray imaging and simulation of the deformation modes in ZnO nanocrystals Mathew Cherukara, Kiran Sasikumar, Wonsuk Cha, Badri Narayanan, Steven Leake, Eric Dufresne, Tom Peterka, Ian McNulty, Haidan Wen, Subramanian Sankaranarayanan, Ross Harder Imaging the dynamic behavior of materials following ultra-fast excitation can reveal insights into the response of materials under non-equilibrium conditions of pressure, temperature and deformation. Such dynamical behavior is extremely challenging to characterize especially at the nano to mesoscopic spatiotemporal scales. We demonstrate three-dimensional imaging of the structure and strain of the transient deformation of a ZnO crystal on sub-ns timescales following excitation by a laser `pump' using stroboscopic `probes' of X-rays. The excitation induced in the ZnO crystal from the laser pump is observed to excite characteristic resonant modes in the crystal at different time scales, corresponding to the propagation of acoustic phonons and the characteristic frequency of the crystal. By directly importing the experimentally reconstructed nanocrystal structure into a continuum deformation model, we elucidate the deformation mechanisms following laser excitation and the development of potential gradients across the nanocrystal with implications for nanoscale power generation. [Preview Abstract] |
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T1.00159: SUPERLATTICES, NANOSTRUCTURES, AND OTHER ARTIFICIALLY STRUCTURED MATERIALS |
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T1.00160: Abstract Withdrawn
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T1.00161: Photon localization in an aperiodic crystal lattice Joseph Holmes, Bogdan Dragnea To design photonic crystals it is essential to engineer the location, size, and shape of the bandgap. In the current study we numerically investigate a conceptually new approach to photon localization in 2D photonic crystal structure in which the underlying lattice is one based on deterministic aperiodic order. The basic model involves parallel dielectric rods arranged on three types of 2D lattices that are fundamentally different: (1) a conventional hexagonal lattice, (2) a random lattice, (3) and a deterministic aperiodic array based on the algorithm of phyllotaxis. From preliminary 2D FDTD calculations, we have seen that conventional crystalline structures, those based on periodicity, do not allow for the isotropic confinement of light. This problem can be solved by designing photonic crystals where the arrangement of dielectrics is based on an algorithm for deterministic aperiodic order. The phyllotactic array adopts an original inflation-deflation symmetry instead of the translational and rotational symmetries of classical crystallography and possesses the highest homogeneity and radial isotropy in the 2D circular domain. Inevitably the aperiodic photonic crystal might be utilized for enhanced light source, waveguide, and in the design of a new class of optical fibers. [Preview Abstract] |
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T1.00162: Active focal control of a metasurface lens based on a graphene-metal hybrid structure Bin Hu, Zi Wang, Juan Liu Metasurfaces are ultrathin films with metallic nano-antennas for generating abrupt wavefront changes of electromagnetic waves. However, the phase modulation is hard to change once a metasurface structure is fabricated. Here we show that, assisted by a monolayer graphene, tunable metasurface devices are able to be realized. Based on Berry geometrical phase, we propose a tunable graphene-metal metalens, which is able to dynamically control the focal length at infrared frequencies. The tunability is achieved by changing the chemical potential of the graphene uniformly. The tuning mechanism is easy to realize in experiments because the graphene chemical potential can be modified by an external gate voltage. Our results have demonstrated that the focal length can be changed from 105$\mu $m to 85$\mu $m continuously when the incident wavelength is 6.6$\mu $m, which illustrates that graphene may be applied for realizing tunable metasurface devices. [Preview Abstract] |
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T1.00163: Wavelength-dependent super-resolution imaging of dye molecules coupled to plasmonic nanotriangles. Esther Wertz, Benjamin Isaacoff, Julie Biteen The emission properties of fluorescent molecules are strongly affected by nearby plasmonic nanoparticles which act as optical nanoantennas. By studying the changes in the single-molecule emission properties, we can learn about the interactions of the fluorophore with its environment. Here, we probe the effects of the excitation and emission wavelengths on the emission patterns from dye molecules coupled to plasmonic nanotriangles, using single-molecule super-resolution imaging. This technique allows the localization of an emitter with a precision much greater than the diffraction limit, by fitting the emission profile to the microscope point-spread function. In order to compare the relative effects of excitation versus emission enhancement, we successively vary laser excitation wavelength, dye emission and absorbance spectra, and local surface plasmon resonance frequency. We demonstrate that the emission pattern is dramatically changed when coupling occurs, and that the emission wavelength of the dye is strongly shifted towards the resonance of the particle it is coupled to. Finally, we show and that large coupling between the dye and gold nanotriangle happens even in the absence of strong intensity enhancement, illustrating the power of super-resolution techniques to investigate light-matter interactions at the nanoscale. [Preview Abstract] |
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T1.00164: Emergence of Chirality from Extreme Anisotropy Michael Melvin, Maxim Durach Metamaterials allow for the engineering of customized responses to electromagnetic radiation. In particular, epsilon-near-zero (ENZ) and epsilon-near-pole (ENP) metamaterials have been designed. Recently it has been shown that thin monolayers of extremely anisotropic metamaterials -- ENZ-ENP metasurfaces, formed by metal nanowires - can exhibit polarization conversion over distances of just 30 nm [1]. This is achieved through difference in phase accumulation for fields polarized along ENZ and ENP directions. When Fabry-Perot resonances corresponding to ENZ and ENP cross, the polarization rotation is obtained. In this work we study a chiral metamaterial composed of stacked ENZ-ENP metasurfaces, each rotated with respect to the other. We show that the spectrum of the rotated structure is similar to the spectrum of the structure without rotation, with the exception that instead of crossings, the ENZ and ENP modes feature anti-crossings, which signify their coupling and formation of a novel type of hybrid chiral resonance. These resonances determine the spectroscopic properties of the resulting chiral structure. References: [1] D. Keene, M. LePain, and M. Durach, ``Ultimately thin metasurface wave plates,'' Annalen der Physik, doi:10.1002/andp.201600005 (2016) [Preview Abstract] |
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T1.00165: Invisibility of a metamaterial without a cloak Reed Hodges, Maxim Durach Invisibility is a major direction in metamaterial research and has been a great source of interest in photonics in recent years. The two primary methods to induce invisibility are transformation optics and plasmonic cloaking. Both of these methods have a well-defined separation of the invisible structure into the hidden and the cloak regions. Here we demonstrate that a solitary wavelength-sized metamaterial object can be designed to be invisible in such a way that it is impossible to define a hidden part and a cloak, since the object responds as homogeneous to light. We show that a radially anisotropic metamaterial sphere serves as an example of such homogeneous invisible object in the visible part of the spectrum and has negligible scattering and extinction normalized total cross-sections (\textless \textless 1) for volumetric metal fractions on the order of 5{\%} up to diameters of the sphere on the order of wavelength. For metaspheres with diameters on the order of 2 wavelengths the normalized cross-sections are highly-reduced (\textasciitilde 1) as compared to purely metal or dielectric spheres of the same geometrical dimensions (for which normalized cross-sections are \textasciitilde 3-4). [Preview Abstract] |
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T1.00166: Employing conserved quantities to control plasmonic fields Matthew LePain, Soheila Mashhadi, Natalia Noginova, Maxim Durach Recently there has been a strong interest in characterization of surface plasmons polaritons (SPPs) using their conserved quantities, such as energy, orbital and spin momenta in plasmonic fields. Absorption of linear momentum of SPPs is proportional to energy absorption and absorption of spin angular momentum, which can be revealed through plasmon drag effect spectroscopy [1]. We use our recently developed semi-analytical method of finding response of square-profile plasmonic structures [2] to study the conserved quantities of plasmonic fields and how they explain the spectroscopic properties of gold square gratings deposited upon thin gold film. This structure supports two types of plasmons on the front and the back side of the grating. Presence of the metal film on the back side produces strong interference of plasmonic fields at the back of the structure and modulation of optical properties related to the back-side plasmons, in particular the reflection from the structure. The strong reflection, intermittent with no reflection, can be explained by formation of new type of angular resonances in the unit cell of the structure. [1] M. Durach, N. Noginova, Phys. Rev. B 93, 161406 (2016). [2] M. LePain, M. Durach, J. of Comp. Sci. Edu. 7, 39 (2016). [Preview Abstract] |
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T1.00167: Influence of gold metallodielectric semi-shell orientation and geometrical irregularities on dark plasmon resonances. Shuang Fang Lim The geometric asymmetry of gold semi-shells leads to orientation and fractional height dependent scattering. The reduced symmetry leads to additional magnetic plasmon resonances. We show scattering of light on semi-shells that is dependent on the fractional height coverage of the gold shell, dependent on its orientation, and positional and number dependence of well-defined protrusions on the semi-shell surface. We qualitatively and quantitatively explain for the contributions of the orientation, fractional height coverage, and the position and number of protrusions to the spectra. The metallic protrusions results in geometrical asymmetry, which leads to excitation of the optically dark quadrupole mode as a function of incident light excitation and polarization. We attribute the far field scattering peaks to the dipole and quadrupole resonances contributed by the protrusions on the semi-shell surface. [Preview Abstract] |
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T1.00168: Abnormal behaviors in galvanically displaced Au nanostructure on silicon below and above percolation threshold a coverage of Au nanostructure. Seung-Hoon Lee, Seongpil Hwang, Jung Hyun Jeong, Jae-Won Jang Temperature dependent resistivity of galvanically displaced Au nanostructure (NS) on $p$-type Silicon ($p$-Si) was investigated by tuning a coverage of Au NS below and above a percolation threshold ($p_{c})$ in temperature range of 10-300K. Below $p_{c}$ [Au nanoparticles are deposited on $p$-Si], the temperature coefficient of resistivity (TCR) and cryogenic sensitivity (S$_{\mathrm{v}})$ of $p$-Si in the low-temperature region (10--30 K) are remarkably improved upto 35{\%} of TCR and 5785{\%} of S$_{\mathrm{v}}$ in Au coverage of 21.9{\%} compared to $p$-Si. Above $p_{c}$ [Au nanofeatures (NFs) are deposited on $p$-Si], the resistivity of the Au NFs on $p$-Si show metal to semiconductor transition (MST) as the temperature increases and the temperature of the MST is tuned from 145 to 232 K as Au{\%} is changed from 82.7 to 54.3{\%}. Our investigation can propose a new optoelectronic application by galvanic displacement method and can provide the better understanding for effect of metal NS on doped semiconductor in the galvanic displacement method. [Preview Abstract] |
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T1.00169: Thermal Conductivities of Semiconducting Nanostructures Alexander Robillard, Ralf Meyer The thermal properties of semiconductors, much like their electrical properties, are of great interest due to their applications in science and industry. In particular, nanostructured materials such as nanowires and nanolattices can exhibit unique thermal properties which can be used in areas such as energy harvesting, thermoelectric materials and computer components. In order to assess the thermal properties of these types of structures, molecular dynamics simulations of silicon and germanium nanostructures have been performed using reverse non-equilibrium molecular dynamics. This method creates an artificial heat flow by interchange of momenta, which allows the measurement of an induced temperature gradient and therefore a value for the thermal conductivity. Results are presented from simulations of nanowires and nanoparticles, and more complex structures built from nanowires and nanoparticles. The temperature profile induced on these structures is presented and their thermal characteristics are examined. [Preview Abstract] |
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T1.00170: Spatial Manipulation of Heat Flow by Surface Boundaries at the Nanoscale Abhinav Malhotra, Martin Maldovan The precise manipulation of phonon transport properties is central to controlling thermal transport in semiconductor nanostructures. The physical understanding, prediction, and control of thermal phonon heat spectra and thermal conductivity accumulation functions - which establish the proportion of heat transported by phonons with different frequencies and mean-free-paths - has attracted significant attention in recent years. In this talk, we advance the possibilities of manipulating heat by spatially modulating thermal transport in nanostructures. We show that phonon scattering at interfaces impacts the most preferred physical pathway used by heat energy flow in thermal transport in nanostructures. The role of introducing boundaries with different surface conditions on resultant thermal flux is presented and methodologies to enhance these spatial modulations are discussed. This talk aims to advance the fundamental understanding on the nature of heat transport at nanoscale with potential applications in multiple research areas ranging from energy materials to optoelectronics. [Preview Abstract] |
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T1.00171: Picosecond laser ultrasonic measurements of surface waves on patterned layered nanostructures Sam Gartenstein, Molly James, Sushant Mahat, Erik Szwed, Brian Daly, Weili Cui, George Antonelli We report ultrafast optical pump-probe measurements of 5 -- 25 GHz surface acoustic waves (SAWs) on patterned layered nanostructures. These very high frequency SAWs were generated and detected on the following patterned film stack: 25 nm physically vapor deposited Al / 60-110 nm thermally grown a-SiO$_{\mathrm{2}}$ / Si (100) substrate. The Al was etched to form lines of rectangular cross section with pitches ranging from 1000 nm down to 140 nm and the lines were oriented parallel to the [110] direction on the wafer surface. The absorption of ultrafast pulses from a Ti:sapphire oscillator operating at 800 nm generated SAWs that were detected by time-delayed probe pulses from the same oscillator via a reflectivity change ($\Delta $R). The SAW frequency increased with decreasing pitch in a non-linear fashion due to dispersion of the wave caused by the presence of the oxide layer. We also experimentally demonstrate the traveling of the SAW's by separating the focused pump and probe laser spots by several microns. We compare the results to coarse-grained molecular dynamics simulations and simplified calculations using isotropic elasticity theory. [Preview Abstract] |
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T1.00172: The influence of the SrTiO$_{\mathrm{3}}$ capping layer to the two-dimensional electron liquid at the interface of LaAlO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$. Akhilesh Singh, MingYuan Song, Chi-Shen Lee, Wei-li Lee The discovery of 2-dimensional electron liquid (2DEL) at the interface of LaAlO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3}}$ (LAO/STO) has attracted enormous interests due to its fascinating behaviours, such as magnetism, superconductivity, and unexpectedly coexistence of the two. Inspired by earlier works, a STO capping layer on LAO/STO can largely affect the electronic reconstruction at the interface, possibly giving rise to a parallel 2D electron-hole bilayer. In this work, we used oxide molecular beam epitaxy technique to grow high-quality films of STO(x nm)/LAO(y nm)/STO(001)(substrate) heterostructures with different x and y values. Influences of the capping layer on 2DEL and related magnetotransport properties will be systematically studied and discussed. [Preview Abstract] |
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T1.00173: Metal to insulator transition in ultrathin SrIrO$_{\mathrm{3\thinspace }}$films Wei Guo, Dianxiang Ji, Zhangwen Mao, Zhengbin Gu, Yuefeng Nie*, Xiaoqing Pan The 5$d$ iridates host a variety of intriguing novel phenomena, such as the spin-orbit Mott insulating state in Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$, the potential superconductivity in doped Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$, and the semi-metallic ground state in SrIrO$_{\mathrm{3}}$. Here, using a combination of reactive molecular beam epitaxy and \textit{in situ} transport measurements, we grew a series ultrathin films of SrIrO$_{\mathrm{3}}$ and observed a metal to insulator transition when the film thickness is below a critical value. [Preview Abstract] |
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T1.00174: A new method for in situ calibration of cation stoichiometry during perovskite growth by RHEED (Reflection High-Energy Electron Diffraction) Kanishka Wijesekara, Qingyu Lei, Maryam Golalikhani, Bruce Davidson, Xiaoxing Xi Reflection High-Energy Electron Diffraction (RHEED) is used in situ in the growth of epitaxial oxide perovskite (ABO$_{3})$ thin films by Atomic Layer-by-Layer Laser MBE (ALL-Laser MBE). Complete layer coverage of a single AO layer or a BO$_{2}$ layer is independently determined by observing the intensity of the diffracted RHEED spot. As the AO and BO$_{2}$ layers are deposited separately, the chemical structure factor and surface roughness is reflected in the intensity. For routine control of film growth, the diffracted intensity is monitored to peak or to bottom by the flux of an elemental oxide source, creating an oscillation of the intensity where one complete cycle is represented by one-unit cell of film growth. To calibrate growth rates, we use a novel method which is more sensitive to the film stoichiometry. An excess A site flux is first provided such that the subsequent growth of stoichiometric unit cells is observed as a split-peak oscillation. Since there are more sharp features in the split peak, this allows for an accurate stoichiometry calibration. This technique was first successfully used by Davidson et al. for Reactive Oxide MBE. Our results further demonstrate that it is a powerful tool for the ALL growth of epitaxial perovskite thin films. [Preview Abstract] |
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T1.00175: Abstract Withdrawn
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T1.00176: Characterizations of ZnO/MoO$_{\mathrm{3}}$ superlattices grown by Atomic Layer Deposition Y.S. Hong, Q.Y. Chen, P.V. Wadekar, W.C. Hsieh, C.F. Chang, H.C. Huang, C.M. Shiau, C.H. Lee, Y.P. Cheng, C.Y. Dang, P.C. Kung, Y.Y. Liang, S.H. Huang, Z.Y. Wu, C.M. Lin, S.T. Yu, L.W. Tu, N.J. Ho, H.W. Seo, W.K. Chu ZnO/MoO$_{\mathrm{3}}$ superlattices (SLS) were prepared by ALD on Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ substrates at 450K. The growth rates are 0.17 per cycle for MoO$_{\mathrm{3}}$ and 1.66 for ZnO, according to XRR. The MoO$_{\mathrm{3}}$ films were found amorphous when deposited separately, while ZnO polycrystalline. However MoO$_{\mathrm{3}}$ became polycrystalline and ZnO textured grown into SLS, as judged by the electron diffraction patterns. The ZnO thicknesses were fixed at 6 nm per period while MoO$_{\mathrm{3}}$ varied from 2 to 6 nm. The nanostructures as examined by TEM indeed show expected periodicity consistent with XRR. HRTEM also gave clear interfaces of the SLS with certain regions of imperfection. Thence, we conclude that amorphous MoO$_{\mathrm{3}}$ would crystallize when grown adjacent to an initial layer of ZnO. PL was employed to investigate the possible variations of their bandgaps when the constituent ZnO and MoO$_{\mathrm{3\thinspace }}$brought together in close proximity of nanoscakes. Electronic band structures according to ab initio calculations will be discussed. [Preview Abstract] |
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T1.00177: Characterizations of ZnO/Ga2O3 superlattices grown by atomic layer deposition. P.C. Kung, Q.Y. Chen, P.V. Wadekar, W.C. Hsieh, C.F. Chang, H.C. Huang, C.M. Shiau, Y.P. Cheng, Y.S. Hong, C.Y. Dang, C.H. Lee, S.H. Huang, Z.Y. Wu, Y.Y. Liang, C.M. Lin, S.T. You, L.W. Tu, N.J. Ho, H.W. Seo, W.K. Chu We have studied the structural and optical properties of ZnO/Ga2O3 superlattices (SLS) grown by ALD on (0001)-Al2O3, (100)- and (111)-Si substrates. Samples were grown followed the ratio of ALD cycles for ZnO (m) to Ga2O3 (n) was fixed at m:n $=$ 2:3, while total thickness is the same for all. The structural properties used XRD and TEM indicate that samples are polycrystalline, while XRR confirmed the presence of SLS structures, albeit with rough interfaces suggesting that epitaxial growth in this system involves complex reaction kinetics. RTPL investigated relevant levels of energy transitions. For the thicker ZnO and Ga2O3 layers we observed a strong band emission peak at 3.36 eV, close to the bandgap of bulk value 3.37 eV. As the ZnO and Ga2O3 thicknesses were reduced, the band emission peak also reduced drastically. The causes behind the optical properties are further discussed in association with the first-principles calculations. [Preview Abstract] |
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T1.00178: Structural and optical properties of epitaxial In2O3/ZnO superlattices C.Y. Dang, Q.Y. Chen, P.V. Wadekar, W.C. Hsieh, C.F. Chang, H.C. Huang, C.M. Shiau, Y.P. Cheng, Y.S. Hong, P.C. Kung, C.H. Lee, S.H. Huang, Z.Y. Wu, Y.Y. Liang, C.M. Lin, S.T. You, L.W. Tu, N.J. Ho, C.H. Liao, H.W. Seo, W.K. Chu Superlattices of shallow quantum well structures with alternating layers of In2O3 and ZnO have been prepared by sputtering at 923K on c-sapphire substrates. Optimization of the processing parameters was attempted through varying the sputtering power, deposition temperature, and number of periods. X-ray reflectivity (XRR) assisted with analytical data fittings was used to extract the thickness, density, and roughness of the samples, while X-ray diffraction (XRD), Grazing Incidence X-ray Diffraction (GIXRD), and phi scans were adopted to verify their epitaxy. The epitaxial qualities for the samples with In2O3 as a starting layer are superior to those starting with ZnO based on transmission electron microscopy (TEM) atomic imaging and electron diffraction. The electronic structures according to the first-principles calculations will be discussed in association with the optical properties inferred from optical transmission and photoluminescence spectroscopy. [Preview Abstract] |
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T1.00179: Structural and optical properties of epitaxial Cu$_{\mathbf{2}}$O ZnO superlattices Y.P. Cheng, Q.Y. Chen, P.V. Wadekar, W.C. Hsieh, C.F. Chang, H.C. Huang, C.M. Shiau, Y.S. Hong, C.Y. Dang, P.C Kung, C.H. Lee, S.H. Huang, Z.Y. Wu, Y.Y. Liang, C.M. Lin, S.T You, L.W. Tu, N.J. Ho, C.H. Liao, H.W. Seo, W.K. Chu Superlattices with alternating layers of Cu$_{2}$O and ZnO have been prepared by magnetron sputtering on -sapphire (Al$_{2}$O$_{3})$ substrates at 650°C. The thickness, density, and roughness of obtained samples were analyzed by X-ray reflectivity (XRR) assisted with meticulous analytical data fittings, while X-ray diffraction (XRD), Grazing Incidence X-ray Diffraction (GIXRD), and phi scans were employed to verify their epitaxial qualities. For the superlattices starting with Cu$_{2}$O, the epitaxy was superior to those starting with ZnO as judged by transmission electron microscopy (TEM) atomic imaging and associated electron diffraction. The electronic band structures based on the first-principles calculations will be illustrated in comparison with the optical transitions inferred from photoluminescence spectroscopy. [Preview Abstract] |
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T1.00180: Role of chemical potential and limitations of growth kinematics on stoichiometry of InSb nanowires Zaina Algarni, Usha Philipose A study of the relationship between chemical potentials of the vapor-liquid and solid phases during indium antimonide (InSb) nanowire growth by VLS process will be presented. Nanowire growth kinematics is governed by interactions between the vapor phase, the spherical alloy droplet and the solid cylindrical nanowire. Using a simple model, the phase stability of the In-Sb liquid alloy droplet will be ascertained and confirmed by experiments. A recent study of the phase diagram of the In-Sb alloy nanoscale system shows a reduction in melting point and eutectic temperature, resulting in a high solubility of In in Sb on the Sb-rich eutectic side and of Sb in In on the In-rich eutectic side of the phase diagram, factors that affect the nanowire growth kinematics. Using the Gibbs-Thomson equation, a relation between supersaturation and concentration of In and Sb in droplet will be obtained. Experimental results showing the diameter dependence on nanowire stoichiometry will be presented with thicker nanowires having higher Sb content and thinner with high In content. . [Preview Abstract] |
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T1.00181: Transport in single InAs Nanowire and Bi2Se3 Flake Photosensitive Devices Seyyedesadaf Pournia, Gabrielle Koknat, Giriraj Jnawali, Howard Jackson, Leigh Smith, Hoe Tan, Chennupati Jagadish, Stephen Wilson We report on preliminary measurements of devices fabricated from single InAs nanowires and exfoliated Bi2Se3 flakes. The Wurtzite InAs nanowires were mechanically harvested from the MOCVD-grown substrates and dispersed onto a Si/SiO2 substrate. The Bi2Se3 flakes were exfoliated from Bi2Se3 single crystals which were grown in a Bridgeman furnace. The 60 to 100 nm thick flakes were dispersed onto a Si/SiO2 substrate. Using photolithography two electrical contacts were defined on either end of the nanowires or flakes by deposition of 20 nm Titanium followed by 300 nm Aluminum. Using a probe station and current amplifier, current-voltage measurements were obtained both in the dark and under white light illumination. Most devices showed I-V behavior consistent with back-to-back Schottky contacts, with some evident photosensitivity under illumination. [Preview Abstract] |
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T1.00182: Magneto-electric effect in Thin Films of Ni-Mn-In Nabil Al-Aqtash, Andrej Sokolov, Renat Sabirianov The magneto-electric effect in Ni-Mn-In thin films deposited on ferroelectric (FE) substrate is studied using DFT- based methods. The off-stoichiometric Ni2Mn1.5In0.5 alloy shows that the ferromagnetic (FM) cubic phase undergoes transformation to tetragonal ferromagnetic (FiM) martensite phase at low temperature. The presence of FE substrate SrZrO3/PbZrO3 alters the relative stability of FM austenite and FiM martensite phases. Furthermore, the polarization reversal in FE changes the energy difference between two phases as well, leading to the prospect of tuning the phase transition temperature by applied electric field. The structure of the interface affects the magnetoelectric coupling. We find that Ni-(Pb-O) interface is the energetically favorable in formation of FE/Ni2Mn1.5In0.5. The energy difference (per NiMnIn f.u) between FM austenite and FiM martensite states of the film on FE substrate is $\Delta $E $=$ 0.22 eV with polarization away from interface, upon polarization reversal $\Delta $E $=$ 0.75 eV, compared to ($\Delta $E $=$ 0.24 eV) in the bulk. These results clearly indicate the possibility of control of martensitic transition in Ni-Mn-In thin films by FE substrate. [Preview Abstract] |
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T1.00183: Europium-Doped Lanthanum Hafnate Nanoparticles: Structure, Photoluminescence, and Radioluminescence Kareem Wahid, Madhab Pokhrel, Yuanbing Mao Due to their novel physical properties, nanostructured phosphors are of interest for radiation-based imaging and therapeutics. Herein, the structural and luminescent properties of europium-doped lanthanum hafnate (La$_{\mathrm{2}}$Hf$_{\mathrm{2}}$O$_{\mathrm{7}}$:xmol{\%}Eu$^{\mathrm{3+}}$, x $=$ 0 - 35) nanoparticles are investigated for use as scintillators. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy confirm samples prepared through a combined co-precipitation and low-temperature molten salt synthetic process homogenously form spherical nanocrystals of $\sim $ 36 nm in the ordered pyrochlore phase. Ultraviolet and X-ray excitation of these samples induce strong red emissions in the 580 - 590 and 612 - 630 nm range corresponding to the $^{\mathrm{5}}$D$_{\mathrm{0}}\to ^{\mathrm{7}}$F$_{\mathrm{1}}$ magnetic dipole and $^{\mathrm{5}}$D$_{\mathrm{0}}\to^{\mathrm{7}}$F$_{\mathrm{2}}$ electric dipole transitions of Eu$^{\mathrm{3+}}$. Optical response and quantum yield are optimized at 5{\%} Eu$^{\mathrm{3+}}$; a proposed trade-off between quenching mechanisms (defect-states/cross-relaxation) and dopant concentration is discussed. Owing to their high density, large effective atomic number, and bright luminescence, these La$_{\mathrm{2}}$Hf$_{\mathrm{2}}$O$_{\mathrm{7}}$:xmol{\%}Eu$^{\mathrm{3+}}$ nanoparticles warrant further investigation for scintillator applications. [Preview Abstract] |
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T1.00184: Study of light scattering by a monolayer of silica spheres Arturo Santos G\'omez, Ana Lilia Gonz\'alez Ronquillo Recent advances in the synthesis of silica (SiO$_2$) periodic structures at micro and nano scale have been led to numerous and diverse applications, for example, as a photonic material or SERS substrate. Model and numerical simulations of the electromagnetic response are crucial to understand the optical behaviour of these structures. In this work, we present numerical calculations of the optical efficiencies of light by an infinite bidimensional array of silica spheres, arranged in a closed packed configuration. The variables considered are: size of the spheres, angle of incidence, and refractive index of the surrounding medium. We have used the very well known Discrete Dipole Approximation to calculate the optical properties of the system. The diameter of the spheres is in the range from $200$ nm to $600$ nm, and we also have considered that the monolayer is embedded in different non absorbing media. The results show an optical bandgap associated with the periodicity of the structure. The bandgap is red-shifted when the size of the spheres is increased and its position depends on the refractive index of the surrounding medium and on the incident angle of light. Our results will provide a basis for future investigations. [Preview Abstract] |
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T1.00185: Understanding Cooperative Chirality at the Nanoscale Shangjie Yu, PengPeng Wang, Alexander Govorov, Min Ouyang Controlling chirality of organic and inorganic structures plays a key role in many physical, chemical and biochemical processes, and may offer new opportunity to create technology applications based on chiroptical effect. In this talk, we will present a theoretical model and simulation to demonstrate how to engineer nanoscale chirality in inorganic nanostructures via synergistic control of electromagnetic response of both lattice and geometry, leading to rich tunability of chirality at the nanoscale. Our model has also been applied to understand recent materials advancement of related control with excellent agreement, and can elucidate physical origins of circular dichroism features in the experiment. [Preview Abstract] |
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T1.00186: Using active gain medium to maximize light absorption Jie Wang, Wenzhe Liu, Dezhuan Han, Xiaohan Liu, Lei Shi, Jian Zi Using an optical nanoresonator, such as a nano-particle, to concentrate and absorb light at the deep subwavelength scale is of both fundamental and practical significance. To quantify the ability of absorption, the absorption efficiency, i.e., the ratio of the absorption cross section of a local resonator to its geometric cross section, is always used. For a deep subwavelength particle, the absorption efficiency is only about 3. To increase the absorption efficiency of a deep subwavelength particle is challenging. In this work, a general method to control the absorption cross section of a deep subwavelength particle by using gain material is proposed and verified theoretically. The maximum absorption cross section, $3\lambda^2/8\pi n^2$, is demonstrated in the visible frequency region with a modest gain coefficient of the order of $10^4$. Moreover, the method has been applied to boost the absorption and the local field enhancement of a single graphene ribbon in the mid-infrared region. It would be emphasized that, this method to increase the absorption of a deep subwavelength particle can be applied to other optical materials. [Preview Abstract] |
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T1.00187: Optical band gap in a nanocomposite structurally chiral medium Carlos Avendaño, Adrián Reyes, Jonatan Mendoza We analyzed the optical band gaps for axially propagating electromagnetic waves throughout a nanocomposite structurally chiral medium. This medium is made of metallic nanoballs (silver) randomly dispersed in a structurally chiral material whose dielectric properties can be represented by a resonant effective uniaxial tensor. The structurally chiral material is taken to possess locally a $\bar{4}2m$ point group symmetry. We found that the band gap properties of the periodic system depends strongly on the volume fraction of nanoparticles in the chiral matrix. Particularly, we observed splitting of the bands and the creation of new sub band gaps when the resonance frequency of the composite medium lies within the band gap without inclusions. [Preview Abstract] |
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T1.00188: Low Intensity UV Treatment of Zinc Oxide Nanocrystal Thin Films Gunnar Nelson, Ben Greenberg, Eray Aydil, Uwe Kortshagen Thin films composed of ZnO nanocrystals (NC) synthesized using nonthermal plasmas show great potential as inexpensive transparent conductors. A compact film of NCs can be formed rapidly via supersonic impaction of the plasma effluent onto a variety of substrates, and the optical and electronic properties of the film can be tuned by changing NC size. However, electron-trapping hydroxyl (OH) groups terminate the surfaces of the as-deposited NCs, resulting in low electrical conductivities. Previously, this problem was solved by infilling the films' pores with Al2O3 via atomic layer deposition (ALD), but this slow post-deposition process is incompatible with rapid thin film production. To develop an alternative to the ALD treatment, we investigate electron trap removal via UV irradiation. We observe that ZnO NCs exposed to UV light centered at 365 nm under an N2 atmosphere show a decrease in OH vibrational absorption as measured by Fourier Transform Infrared Spectroscopy (FTIR). A localized surface plasmon resonance (LSPR) feature corresponding to a free electron density on the order of 1019 cm-3 emerges in the FTIR spectrum after two seconds of UV exposure. Subsequent air exposure brings back the OH absorption and eliminates the LSPR. We explain the free electron photogeneration in terms of interactions between photogenerated excitons and electrons trapped by OH groups. [Preview Abstract] |
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T1.00189: Electromagnetic Wave Transmission Through a Nano-hole in a Plasmonic Layer: Near zone. Désiré Miessein, Norman Horing, Harry Lenzing, Godfrey Gumbs We present an analysis of the role of incident angle on the transmission/diffraction of an electromagnetic wave through a nano-hole in a plasmonic layer in the near zone. Detailed calculated results are exhibited. [Preview Abstract] |
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T1.00190: Measurement of resistance switching dynamics in copper sulfide memristor structures Kaitlin McCreery, Matthew Olson, Stephen Teitsworth Resistance switching materials are the subject of current research in large part for their potential to enable novel computing devices and architectures such as resistance random access memories and neuromorphic chips. A common feature of memristive structures is the hysteretic switching between high and low resistance states which is induced by the application of a sufficiently large electric field. Here, we describe a relatively simple wet chemistry process to fabricate $Cu_{2}S/Cu$ memristive structures with $Cu_{2}S$ film thickness ranging up to 150 micron. In this case, resistance switching is believed to be mediated by electromigration of $Cu$ ions from the $Cu$ substrate into the $Cu_{2}S$ film. Hysteretic current-voltage curves are measured and reveal switching voltages of about 0.8 Volts with a relatively large variance and independent of film thickness. In order to gain insight into the dynamics and variability of the switching process, we have measured the time-dependent current response to voltage pulses of varying height and duration with a time resolution of 1 ns. The transient response consists of a deterministic $RC$ component as well as stochastically varying abrupt current steps that occur within a few microseconds of the pulse application. [Preview Abstract] |
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T1.00191: Density functional Study of \textbraceleft 210\textbraceright -Faceted Pd Nanocrystals in Polyvinylpyrrolidone Solution YUSHENG HOU, Wenpei Gao, Xiaoqing Pan, Ruqian Wu Nanostructures with well-defined sizes and shapes can potentially realize a plethora of unique applications, such as sensing, catalysis, photonics, electronics, and medicine. It is highly desired that specified shapes and sizes of nanocrystals can be engineered by utilizing structure-directing agents. Our experimental measurements showed that the metal Palladium (Pd) nanostructures have more stable \textbraceleft 210\textbraceright facets in the polyvinylpyrrolidone (PVP) solution, which is different from the Pd nanoclusters in vacuum. Based on the density functional theory (DFT) along with the van der Waals (vdW) correction, we have studied the interaction of a 2-pyrrolidone (2P) ring, a submolecule of PVP, with various Pd surfaces. Our calculations indicate that 2P binds to the Pd surface via the oxygen, more strongly to the \textbraceleft 210\textbraceright facet than to \textbraceleft 001\textbraceright and \textbraceleft 111\textbraceright facets. As a result, the \textbraceleft 210\textbraceright facet becomes the preferential orientation so the Pd nanoclusters may grow in a star-shape, which explains our experimental observations. [Preview Abstract] |
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T1.00192: Electronically tunable metamaterials using subwavelength magnetoresponsive particles Monica Allen, Jeffery Allen, Jacob Parrow, Sajid Asif, Adnan Iftikar, Brett Wenner, Benjamin Braaten We demonstrate tunability of material properties of an engineered electromagnetic material in the RF regime using microparticles that respond to static magnetic biasing fields. The magnetic particles align with field lines creating a short/inductive state of the switch in the addressed voxel. When the biasing magnetic field is removed, the switch returns to an open/capacitive state. Each voxel measures 1.5 mm x 1.5 mm x 0.508 mm in the x, y, and z direction respectively, with a 0.9 mm diameter cylindrical cavity. The cavity is along the z-axis and is partially filled with microparticles composed of a magnetite core with Ag coating. Cu foil placed on the top and bottom encloses the particles in the cavity and acts as the biasing electrodes. Switching between inductive and capacitive states in spatially addressed voxels controls the cumulative $\varepsilon $ and $\mu $ of the host material (i.e., layer) and controls the phase of an incident wave. We present finite element based models of prototype voxels with experimental measurements that validate the models on a host. This research can be applied to real-time tuning of material parameters with subwavelength voxel precision enabling wave control/manipulation as well as devices for switching and software-dictated tunable impedance capabilities. [Preview Abstract] |
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T1.00193: SURFACES, INTERFACES AND THIN FILMS |
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T1.00194: Inter-diffusion of copper and hafnium as studied by x-ray photoelectron spectroscopy Justin Pearson, A. R. Chourasia The Cu/Hf interface has been characterized by x-ray photoelectron spectroscopy. Thin films (thicknesses ranging from 100 nm to 150 nm) of hafnium were deposited on a silicon substrate. About 80 nm of copper was then deposited on such samples. The e-beam method was used for the deposition. The samples were annealed for 30 min at temperatures of 100, 200, 300, 400, and 500\textdegree C. The inter-diffusion of copper and hafnium was investigated by sequential sputter depth profiling and x-ray photoelectron spectroscopy. The interdiffusion in each case was analyzed by the Matano-Boltzmann's procedure using the Fick's second law. The interdiffusion coefficients and the width of the interface as determined from the data have been correlated with the annealing temperature. [Preview Abstract] |
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T1.00195: Ion beam induced hot electron excitations in thin metal films Dhruva Kulkarni, Daniel Field, Daniel Cutshall, James Harriss, William Harrell, Chad Sosolik We present measurements on hot carrier excitations in a metal irradiated by hyperthermal energy ions. Specifically, alkali (Rb$^{\mathrm{+}})$ and noble gas(Ar$^{\mathrm{+}})$ ions were used to irradiate a Schottky diode consisting of a thin film of Ag (\textasciitilde 25nm) grown on an n-type Si (111) wafer. Measurements of the resultant current through the device were performed as a function of energy and angle of incidence of the incoming ions. Energy loss of the incident energetic ions inside the metal film leads to the generation of hot carriers which are detected as a kinetically-induced current or ``kinecurrent'' within the device, analogous to previous measurements of ``chemicurrent'' [H. Nienhaus, \textit{Surface Science},\textbf{ 45}, 1-78 (2002)]. We observe the existence of a threshold with respect to the energy of the incoming ions for the generation and detection of hot electrons using Schottky diodes. [Preview Abstract] |
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T1.00196: Interface Characterization of PEDOT:PSS on ITO Using Photoelectron Spectroscopy Lynette Kogler, Marc Haeming, Clemens Heske Solution-processed organic materials are appealing for use in printable electronics as a means to lower production costs, but precise control of the process is crucial for the achieving the desired properties in the final material. Electronic interface properties depend on both the material and the fabrication process, impacting the development and commercialization of organic electronic materials. This research explores the surfaces of and the interface between two materials widely used in organic electronics: poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and indium tin oxide (ITO). Spin coating was used to make thin films of both PEDOT:PSS and ITO, the latter made with a metal-organic precursor solution. PEDOT:PSS films were applied to substrates of solution-processed ITO and commercially produced ITO, and the surfaces and interfaces were characterized using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). Inhomogeneities in the PEDOT:PSS films have been observed within individual samples. The impact of these on the surface electronic properties and the implications for organic electronic devices will be discussed. [Preview Abstract] |
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T1.00197: Surface wettability modification of CVD-grown MoS$_{2}$ by oxygen plasma treatment Hyukjoon Kwon, Yunjeong Park, Youngchan Kim, Changgu Lee, Kyunghoon Kim Two dimensional MoS$_{2}$ FET (field-effect transistor) has been emerging as an outstanding semiconductor device platform for bio-sensor. MoS$_{2}$ FET has not only a good stability in electrolyte and pH changes but also tunability for surface engineering, which provides a good opportunity for bio-sensor platforms. Recently many studies have been reported on electronic and optical properties of MoS$_{2}$ while less effort has been made to investigate the surface wettability of CVD-grown MoS$_{2}$ and modification of atomically layered MoS$_{2}$ surface property. In this study, we investigated the surface energy of MoS$_{2}$ with various layer thickness (1L, 2L and 3L) and effect of O$_{2}$ plasma treatment. We synthesized mono- to tri-layer of large-area MoS$_{2}$ with CVD (chemical vapor deposition) method and conducted surface characterization of MoS$_{2}$ supported on SiO$_{2}$/Si substrate using atomic force microscopy and contact angle measurement. We show tunable wetting properties of plasma-engineered MoS$_{2}$. [Preview Abstract] |
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T1.00198: Effects of large critical cluster size in thin-film nucleation and growth models: deviation of island- and capture-zone size distributions from standard models. Linnea Bavik, Brad Johnson, Cyrus Schaaf, Michael Jenkins, David Patrick Submonolayer island formation in molecular and metallic thin films prepared by vacuum deposition is typically characterized by a small critical nucleus size, i* \textasciitilde 1 -- 3 monomers. However, comparable nucleation kinetics in a liquid solvent environment involves critical nuclei sizes an order of magnitude (or more) larger, an important regime that has not been well explored by theory. Here we examine the effects of large critical nucleus size on nucleation and growth kinetics via kinetic Monte Carlo simulations of burst nucleation, treating extended fractal, compact circular, and point island models. In extended models, following a short burst of nucleation, the rate of island growth is proportional to island size, causing small initial size differences to become exaggerated as growth proceeds. This effect becomes more pronounced as the critical nucleus size increases, where the average monomer density, and hence nucleation behavior, is more sensitive to the proximity of islands. This leads to deviations in the resulting island size distribution from the predictions of standard models. [Preview Abstract] |
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T1.00199: Submonolayer Crystalline Tetracene Film Formation by Vapor-Liquid-Solid Deposition. Cyrus Schaaf, Michael Jenkins, Linnea Bavik, Brad Johnson, David Patrick Over the last several decades, studies of submonolayer nucleation and growth kinetics by vacuum deposition have produced a sophisticated understanding of the connections between structural film properties such as island size distributions, island density, inter-island spacing statistics, nucleation and growth rates, with underlying atomistic process of monomer deposition, diffusion, and aggregation. By comparison, the comparable theoretical understanding of polycrystalline films formed in liquid solvent environments is much less well developed. Here~we present studies into the early stage nucleation and growth kinetics of organic molecular films of tetracene prepared by a vapor-liquid-solid deposition technique in which tetracene monomers are delivered at a constant rate via a vapor-phase flux to a substrate coated with a sub-micron thick layer of an organic liquid solvent, causing crystals to nucleate and grow. We use in-situ, real-time fluorescence videomicroscopy to follow the formation and growth of individual crystals, including simultaneous spatial mapping of the monomer concentration and depletion zones. [Preview Abstract] |
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T1.00200: Emission Enhancement in Quantum Emitters - Plasmonic Nanostructures Systems Aeshah Muqri, Jae Yong Suh In this poster, the emission enhancement probed by spectroscopic and dynamic means will be presented. Systems composed of quantum emitters ensembles in the vicinity of plasmonic structures were fabricated. Their coupling strength were investigated by measuring the reflection, steady state photoluminescence, and time resolved fluorescence. [Preview Abstract] |
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T1.00201: Structural and optical properties of Bismuth Selenide (Bi$_{\mathbf{2}}$\textbf{Se}$_{\mathbf{3}}$\textbf{) thin films: Thickness and substrate dependence} Yub Raj Sapkota, ASMA ALKABSH, Aaron Walber, Sarah Kovac, Hassana Samassekou, Dipanjan Mazumdar Bi$_{2}$Se$_{3}$ is a topological insulator that has gained much attention in both theoretical and experimental condensed matter due to its inherently fascinating structural property of acting like a metal on the surface and an insulator in the bulk form. Here we report on structural and optical properties of Bismuth Selenide thin films of various thickness (10 QL to 90 QL), and grown on different substrates by means of magnetron sputtering. Structural and interface properties are characterized by means of high-resolution X-ray diffraction and reflectivity. Spectroscopic ellipsometry and Reflectance/UVVIS spectroscopy is used to understand their optical properties. Our results indicate a successful growth of few layer Bi$_{2}$Se$_{3}$ on all substrates with Al$_{2}$O$_{3\, }$distinguishing itself by its atomically smooth feature. Variation of electronic properties with thickness and substrate will be discussed. [Preview Abstract] |
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T1.00202: Metal (Ag) Nanoparticles on Thin Film Solar Cells Olivia Rodgers The research and development of cheaper and more efficient photovoltaic cells to harness the sun's energy and convert it to electricity is a necessity in the nearing future. The addition of metal nanoparticles to photovoltaic cells creates the possibility of improving cell efficiency and reducing production costs. With the addition of metal nanoparticles incoming light will be scattered and trapped thus enhancing absorption causing less energy to be lost. This is due to more electron and hole pairs being created by absorbed photons producing a larger electrical current compared with a solar cell made with the absence of metal nanoparticles. In the process of creating these cells CdTe and CdS is deposited by method of Pulsed Laser Deposition (PLD) onto glass. Silver (Ag) nanoparticles will be added between the CdS layer and the CdTe layer by the use of PLD. In order to structurally and electrically characterize the silver nanoparticles added efficiency to the cells we will use x-ray diffraction ellipsometry (structural), and Labveiw assisted Keithley source meter photovoltaic measurement set (electrical). The the independent variation of the silver particle size and particle distance on the thin films to determine the optimal electrical energy output will be discussed. [Preview Abstract] |
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T1.00203: Stabilization of Solid Oxide Fuel Cells with Yttrium Based Zirconium Oxide William Cockerell, Chris Ciccarino, Patrick Wadie-Ibrahim, M. Alper Sahiner Solid Oxide fuel cells (SOFC's) is a device that is used to convert chemical energy from a fuel, such as hydrogen or methane, into electricity through electrochemical reactions. These fuel cells are able to deliver highly efficient electrical conversions. Further advantages of SOFC's include; the high amount of heat enthalpy that is given off by the fuel cell operating at temperatures of 800 to 1,000$^{\mathrm{\thinspace }}$degrees Celsius, the modular nature of SOFC's which offers the ability to build larger systems with subsystems of SOFC's in planning of power generation capacity, and the carbon dioxide emission is considerably reduced. It can be seen why these devices are focus of research. In our lab at Seton Hall University, we are attempting to stabilize solid oxide fuel cells with Zirconium (IV) oxide and Yttrium nanoparticles by deposition of (Y)ZrO$_{\mathrm{2\thinspace }}$onto the anode of our cell as our electrolyte. One technique of chemical deposition of (Y)ZrO$_{\mathrm{2\thinspace }}$onto our anode is by using Pulsed Laser Deposition (PLD). The structural and electrical characterization of the thin films will be presented and electrical performance will be correlated by the deposition conditions. The major purpose of this project is to successfully and efficiently deposit Zirconium oxide and Yttrium nanoparticles to the anode of our SOFC in able to slow degradation of the SOFC's through stabilization, making their use more profitable. [Preview Abstract] |
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T1.00204: Molecular Beam Epitaxial growth of Pristine and Cobalt doped Anatase TiO$_{\mathrm{2}}$ thin films and their Enhanced Magnetic and Optical properties Swaleha Naseem, Igor V. Pinchuk, Adam S Ahmed, Yunqiu Kelly Luo, Roland Kawakami, Wasi Khan, Shakeel Khan, Alim H. Naqvi The epitaxial growth of pristine and Cobalt doped Anatase TiO$_{\mathrm{2}}$ (Ti$_{\mathrm{1-x}}$Co$_{\mathrm{x}}$O$_{\mathrm{2}}$, 0.02$\le $ x $\le $0.08) on LaAlO$_{\mathrm{3}}$ (100) has been carried out with goal of getting enhanced magnetic and better optical properties with good structural quality. We have grown pristine and cobalt doped anatase TiO$_{\mathrm{2}}$ thin films with MBE showing good crystalline nature as depicted by the RHEED images with slow growth rate taken over a substrate temperature of 600- 650\textdegree C on LaAlO$_{\mathrm{3}}$ (100). Films were grown in the presence of molecular oxygen while previously reported growth of these oxide films were with OPAMBE or by using ozone flux. Formation of smooth and single phase crystalline nature of the thin film is confirmed by XRD and AFM, EDS. Enhanced magnetism due to oxygen vacancies and doping of Co in the host lattice which is measured by SQUID and the temperature dependent magnetic measurements predicts the curie temperature just above the 300K. The photoconductivity measurements of these thin films gives the photosensitization of anatase titania with transition metal dopants. [Preview Abstract] |
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T1.00205: Conducting Polymer Contacts of Thin Film Solar Cells via Dip Coating Jeffrey Larson, Christopher Ciccarino, Darren Lesinski, Alper Sahiner ZnO photovoltaic solar cell is a commonly researched method for solar cells, but often yield a high resistance. Coating the ZnO in a conductive polymer such as PANI or Pedot will theoretically lower the Schotky Barrier between the anode and the cathode making the cell more efficient. By using a dip coating method, we will be lowering the experimental and production cost as compared to pulsed laser deposition (PLD). The ZnO will be deposited onto an indium tin oxide (ITO) coated glass with the PLD method. The Polymer coating experimental samples will be produced at different temperatures and at several rates of extraction to determine the practices. Ellipsometry will measure the thickness of the Zinc Oxide film and the thickness of the conducting polymer film. The structure of the films will be analyzed through X-Ray Diffraction. A Keithley Source Meter will be used to analyze the photovoltaic properties of the cells to be recorded. The photovoltaic properties of each trial will be discussed in regards to the structure, thickness, temperature and rate of extraction from the coating polymer bath. [Preview Abstract] |
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T1.00206: CVD Growth of Bi$_2$Se$_3$ Crystals Ryuta Yagi, Taishi Takegawa We have studied condition for CVD Bi$_2$Se$_3$ growth in detail. Morphology of grown crystal varied drastically depending on temperature of substrate, flow rate of transport gas, temperature of source materials and catalysts. At an optimum condition we could obtain thin single crystals which were hexagonal in shape. At lower temperatures, we have obtained thin wire single crystals. Magneto transport measurement indicated signature of weak anti-localization. Carrier mobility was as large as 2700 cm$^2$/Vs, however two-dimensional carrier density was significantly large $\sim$3.6$\times$10$^{13}$ cm$^{-2}$ possibly due to vacancy of Se atoms. [Preview Abstract] |
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T1.00207: Thin film deposition using rarefied gas jet Dr. Sahadev Pradhan The rarefied gas jet of aluminium is studied at Mach number \textit{Ma }$=$\textit{ (U\textunderscore j / }$\backslash $\textit{sqrt\textbraceleft kb T\textunderscore j / m\textbraceright )}in the range \textit{.01 \textless Ma \textless 2}, and Knudsen number \textit{Kn }$=$\textit{ (1 / (}$\backslash $\textit{sqrt\textbraceleft 2\textbraceright }$\backslash $\textit{pi d\textasciicircum 2 n\textunderscore d H)} in the range \textit{.01 \textless Kn \textless 15}, using two-dimensional (2D) direct simulation Monte Carlo (DSMC) simulations, to understand the flow phenomena and deposition mechanisms in a physical vapor deposition (PVD) process for the development of the highly oriented pure metallic aluminum thin film with uniform thickness and strong adhesion on the surface of the substrate in the form of ionic plasma, so that the substrate can be protected from corrosion and oxidation and thereby enhance the lifetime and safety, and to introduce the desired surface properties for a given application. Here, $H$is the characteristic dimension, \textit{U\textunderscore j}and \textit{T\textunderscore j}are the jet velocity and temperature, \textit{n\textunderscore d}is the number density of the jet, $m$and $d$ are the molecular mass and diameter, and \textit{kb}is the Boltzmann constant. An important finding is that the capture width (cross-section of the gas jet deposited on the substrate) is symmetric around the centerline of the substrate, and decreases with increased Mach number due to an increase in the momentum of the gas molecules. DSMC simulation results reveals that at low Knudsen number \textit{((Kn }$=$\textit{ 0.01);}shorter mean free paths), the atoms experience more collisions, which direct them toward the substrate. However, the atoms also move with lower momentum at low Mach number$,$which allows scattering collisions to rapidly direct the atoms to the substrate. [Preview Abstract] |
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T1.00208: Effects of thickness and substrate properties on cracks in thin films bonded to an elastic substrate Dong Hyun Kim, Won Bo Lee Cracks occurring in thin films caused by residual tension can change desired film properties and lead to flaws or failures. Since the geometry of cracks or flaws is governed by the fracture properties of the interface and the substrate, in addition to known effects of film thickness, we investigate crack formations according to the film thicknesses using thermal deposition. Also by using different kinds of substrates and films, the effects of residual stress and elastic moduli on crack formation are investigated. As a result, several dimensionless quantities describing the cracks of thin films can be introduced. [Preview Abstract] |
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T1.00209: The effect of misfit strains on ferroelectric domain formation at the morphotropic phase boundary Zhen Liu In the morphotropic phase boundary region where tetragonal and rhombohedral phases coexist in the ferroelectric solid solution PbZr$^{1-x}$Ti$^{x}$O$^{x\, }$(PZT), large strains can be induced at the interface due to the lattice misfit of the two structures. We show that for bulk PZT the misfit strains between tetragonal and rhombohedral phases can lead to an adaptive monoclinic structure in the morphotropic phase boundary (MPB) region, similar to the effects of misfit strains between a crystal and substrate in epitaxial ferroelectric thin films. We use Landau theory to sixth order in polarization to provide insight into factors controlling the occurrence of the monoclinic phase in the MPB region. [Preview Abstract] |
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T1.00210: Structural and optical characterization of ZnO nanostructured thin films. J. C. Gonzalez Gonzalez, M. Urbina Yarupetan Magnetron sputtering is surely the most common technique in the industry for large-scale growth for thin films with low emissivity, where the oxide deposited is usually ZnO. One of the recognized advantages of this technique is that the effects due to ion bombardment contribute to obtain surfaces with very little roughness, in the order of nanometers, and therefore improves the quality of the silver layer deposited at the end in windows with low emissivity. Therefore, a complete characterization of the surface layers of ZnO is required. In this sense, we have analyzed three thin layers of ZnO grown on commercial glass substrates deposited by the magnetron sputtering technique with thicknesses of 20, 50 and 100 nm. We used techniques such as: XRR, XRD, SEM and Raman spectroscopy, to assess roughness, microstructure, ZnO phonons profile and other properties like as density and refraction index. The X'Pert reflectivity program was used to fit the reflectivity data; the intensity of reflections was modeled through homogeneous and uniform layers with a well-defined limit to take into account the glass substrate. Finally, the structural results were correlated with the optical results. [Preview Abstract] |
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T1.00211: Surface roughness effect on Adhesion-Debonding of soft thin elastic film Satish Mishra, Jayati Sarkar Topologically patterned thin film surfaces have been used widely to enhance the modern day technologies. The key property of these materials is a high surface-to-volume ratio that is achieved through patterning their surfaces. These patterns can further be exploited to induce surface properties like adhesiveness, hydrophobicity etc. However, patterning these films through bottom-up approach is uneconomical. One of the top-down approach involves self-organization of soft elastic film in proximity contact of an external contactor. The interplay of elastic and contact force leads to formation of patterns on the film surface. However, the patterning lengthscales are limited to the mean thickness, h, of the film (3h-4h). Here, we have performed Finite Element Analysis (FEA) of the soft thin elastic film (500nm) bonded to a rigid rough substrate in contact proximity of rigid contactor. It is also shown that highly miniaturized patterns can be produced utilizing the inherent roughness of the substrate without resorting to pre-patterning of the substrate to a definite regular form. The results also reveals how the miniaturized lengthscales help these films to behave as better adhesives. [Preview Abstract] |
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T1.00212: The effects of adsorbates on surface morphologies and energies of iron-gallium alloys Hui Wang, Alison Flatau, Ruqian Wu Materials with large magnetostriction are extensively used in sensors, actuators, micro electromechanical systems, and energy-harvesters. Fe-Ga alloys (Galfenol) are very promising rare-earth free magnetostrictive materials. Investigation on surface energies of Galfenol based on density functional calculations (DFT) may provide fundamental understandings and guidance to further optimize the performance of Galfenol. Our DFT calculations predict that Ga-covered (110) surface of Galfenol is more stable in Ga-rich condition, while Ga-covered (001) surface become more favorable in Ga-poor condition, consistent with experimental observations. Moreover, we also study the environmental effects on surface energies of Galfenol and find that chemically adsorbed atoms (e.g. oxygen atoms) may change the surface energies, pointing out a feasible way of tuning the surface orientation of Galfenol to maximize its magnetostriction for practical application. [Preview Abstract] |
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T1.00213: Sulfur adatom adsorption on $\alpha $-Fe$_{\mathrm{2}}$O$_{\mathrm{3}}$~(0001) film studied by DFT$+$U method Jiao An, Prabath Wanaguru, Congxin Xia, Meng Tao, Qiming Zhang The geometric and electronic properties of a sulfur (S) atom adsorption on the hematite~$\alpha $-Fe$_{\mathrm{2}}$O$_{\mathrm{3}}$~(0001) film with have been investigated systematically by calculations based on the density functional theory. The most stable hematite~$\alpha $-Fe$_{\mathrm{2}}$O$_{\mathrm{3}}$~(0001) film with an anti-ferromagnetic arrangement is identified. The S adatom prefers to bond with three O atoms, in the center of a triangle formed by the three O atoms. The S acts as a cation at this site. The sulfur adsorption has introduced two gap states, in addition to the unoccupied surface states. Furthermore, with the most stable S-adsorption configuration, the diffusion of the S adatom from the surface to the inside is searched and the transition state along the minimum-energy pathway is also identified. The isovalent doping of S inside of the film has also been studied. [Preview Abstract] |
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T1.00214: Epitaxial growth and electron doping of Ba$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ films by molecular beam epitaxy Dianxiang Ji, Lin Xie, Zhengbin Gu, Peng Wang, Yuefeng Nie*, Xiaoqing Pan Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ has been shown to share many common key signatures of superconductivity with cuprates, such as Fermi arcs and $d$-wave band gap. However, it is difficult to effectively dope enough charge carriers into Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ and drive them into the potential superconducting state. Ba$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ has a number of distinct advantages over Sr$_{\mathrm{2}}$IrO$_{\mathrm{4}}$, such as the straight Ir-O-Ir bonds, providing another great system to be explored. Here, using reactive molecular beam epitaxy, we successfully grew epitaxial thin films of Ba$_{\mathrm{2}}$IrO$_{\mathrm{4}}$ and doped them through chemical substitutions and surface doping with alkaline metal. [Preview Abstract] |
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T1.00215: Benzene and pyridine on silicon (001) : a trial ground for long-range corrections in density functional theory Oliver Warschkow, Jennifer Bennett, Jill Miwa, David McKenzie, Nigel Marks The adsorption chemistry of benzene and pyridine on the silicon (001) surface is characterised by two prominent adsorbate configurations: a precursor structure bonded to a single Si-Si dimer and a “tight-bridge” configuration that bridges between two adjacent dimers. We examine here the performance of 20 density functionals to predict the relative stability of these two configurations. Disagreements between the predicted and experimentally observed preference point to the importance of long-range exact-exchange terms in these adsorbate systems. These corrections however tend to be detrimental to the prediction of adsorption and activation energies. We discuss this conundrum in terms of systematic exchange-correlation errors that scale with the number of molecule-surface bonds. [Preview Abstract] |
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T1.00216: Observation of oscillatory relaxation in the Sn-terminated surface of epitaxial rock-salt SnSe $\{111\}$ topological crystalline insulator Wencan Jin, Jerry Dadap, Richard Osgood, Suresh Vishwanath, Huai-Hsun Lien, ALEXANDER CHANEY, Huili Xing, Jianpeng Liu, Lingyuan Kong, Junzhang Ma, Tian Qian, Hong Ding, Jerzy Sadowski, Zhongwei Dai, karsten Pohl, Rui Lou, Shancai Wang, Xinyu Liu, Jacek Furdyna Topological crystalline insulators have been recently observed in rock-salt SnSe $\{111\}$ thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation is a preferred configuration. In this work, synchrotron-based angle-resolved photoemission spectroscopy, along with density functional theory calculations, are used to demonstrate conclusively that a rock-salt SnSe $\{111\}$ thin film has a stable Sn-terminated surface. These observations are supported by low energy electron diffraction (LEED) intensity-voltage measurements and dynamical LEED calculations, which further show that the Sn-terminated SnSe $\{111\}$ thin film has undergone an oscillatory surface structural relaxation. In sharp contrast to the Se-terminated counterpart, the Dirac surface state in the Sn-terminated SnSe $\{111\}$ thin film yields a high Fermi velocity, $0.50\times10^6$m/s, which may lead to high-speed electronic device applications. [Preview Abstract] |
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T1.00217: GENERAL PHYSICS |
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T1.00218: A quantum particle in a high-symmetry two-dimensional box Maximilliaan Koopman, Andrew Davis, Qing Wang, Antonett NunezdelPrado, Constance Doty, Tristan Reynoso, Richard Klemm We present contour-plot representations of the low-energy wave functions for a quantum particle in a two-dimensional infinite well potential exhibiting perfect $C_{\infty}$ (disk), $C_{2v}$, (rectangular), $C_{3v}$ (equilateral triangular), or $C_{4v}$ (square) point group symmetry. The rotationally-invariant $C_{\infty}$-allowed wave functions have the integer quantum numbers $n\ge1$. For the rectangular box, all wave functions with $n,n'\ge1$ are allowed, and each one is an allowed representation of the $C_{2v}$ point group. However, for the equilateral-triangular and square boxes, some quantum numbers have to be eliminated, as the wave functions to which they correspond cannot be made into representations of the respective $C_{3v}$ or $C_{4v}$ point groups. For the equilateral triangular box, only $|n-n'|=3p$ are allowed, where $p\ge0$ for the wave functions even about the three mirror planes, and $p\ge1$ for wave functions odd about the three mirror planes. For the square box, $|n-n'|=2p$ are allowed, where for $p\ne0$, only the sum and difference of the two degenerate wave functions are representations of the $C_{4v}$ point group. [Preview Abstract] |
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T1.00219: A quantum particle in a cubic box Andrew Davis, Maximilliaan Koopman, Qing Wang, Constance Doty, Christopher Arose, Eric Apfel, Richard Klemm We study the role of O point group symmetry on the wave functions of a quantum particle in a cubic box, for which the potential energy is zero inside the box and infinite outside it. In order to picture the low-energy wave functions, we use a Mathematica moving script that rotates the cube slowly enough that one can decide whether a given possible wave function obeys all of the symmetry operations of the point group. The rules for allowable wave functions with quantum numbers $(n_1,n_2,n_3)$ are determined and the a set of low-energy wave functions will be shown in color-coded movies of rotating boxes. [Preview Abstract] |
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T1.00220: Exact Analytical Interconversion Between Durometer Hardness Scales A. Jeffrey Giacomin, Peter H Gilbert Previous work has related Young's modulus to durometer hardness for any standardized scale. In this paper, we build on this work to solve explicitly and exactly for the hardness in any one standardized durometer hardness scale as a function of the hardness in any other target scale. We find that when the target scale is for a flat indenter, the conversion is algebraic and straightforward. However, when the target scale is for an indenter that is not flat (conical or hemispherical), the exact explicit analytical solution requires a power series inversion, said series involving beta functions and solutions to a set of integer equations. [Preview Abstract] |
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T1.00221: Patterning of Periodic Ripples in Monolayer MoS$_{2}$ by Using Laser Irradiation Sung Ho Jhang, Sung Won Kim, Jeong Hyeon Na, Won Lyeol Choi, Hyun-Jong Chung, Soo Ho Choi, Woochul Yang, Sang Wook Lee We have investigated the effect of laser irradiation on monolayer MoS$_2$ and observed the swelling-up of the monolayer from the SiO$_2$ substrate upon laser illumination. The mismatch in the thermal expansion between the substrate and MoS$_{2}$ can result in the structural deformation. Employing this method, one can induce structural deformation in a desired pattern, and demonstrate the patterning of periodic ripples in monolayer MoS$_2$ by using laser irradiation. The controlled fabrication of the ripple structure may be instrumental in understanding the effect of ripples on the interesting properties of monolayer MoS$_2$. [Preview Abstract] |
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T1.00222: Characterization of Laser Thinned Molybdenum Disulfide Nano Sheets Abdullah Alrasheed, Nourah Alrubaiq, Fadhel Alsaffar, Koo-Hyun Chung, Frank DelRio, Moh. R. Amer Transition Metals Dichalcogenide (TMDC) materials have attracted the scientific community due to their unique optical, mechanical, and electronic properties. Molybdenum disulfide (MoS$_{\mathrm{2}})$, an emerging 2D material, exhibit a tunable band gap that strongly depends on the numbers of layers, which makes MoS$_{\mathrm{2\thinspace }}$an attractive candidate for optoelectronic applications. However, recent reports have shown that engineering a monolayer using laser thinning can be an effective method without oxide formation, which can be a promising technique for various applications. Here, we investigate this laser thinning process using Raman spectroscopy, \textmu -XPS, and AFM measurements. Our results show that laser thinned MoS$_{\mathrm{2}}$ exhibit a large oxide on the surface of the flake. This oxide cannot be detected using \textmu -Raman spectroscopy, contrary to \textmu -XPS and AFM measurements. We also show that monolayer MoS$_{\mathrm{2}}$ exhibit distinctive phonon behavior compared to multilayer MoS$_{\mathrm{2}}$, which is readily reflected on the vibrational modes intensities. Our results shed light on the topology of laser thinned MoS$_{\mathrm{2}}$ flakes for future optoelectronic and electronic applications. [Preview Abstract] |
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T1.00223: Impurity States on the Kagome Lattice Using Green's Function Method Mohammad Mahdi Valizadeh, Sashi Satpathy The kagome lattice is a 2D lattice that has been of recent interest owing to its graphene-like band structure, the existence of flat band states and exotic quasiparticle excitations. Materials hosting the kagome lattice such as the rare-earth compound RCo$_5$ and the herbertsmithites have been recently synthesized and efforts have been made to change the Fermi energy to the Dirac-like point by introducing impurities into this system. In this work, we study the electronic states introduced by impurities in the system by applying the Green's function approach within a tight-binding model Hamiltonian. The impurities introduce localized states close to the Dirac point, in many ways similar to graphene, which will be discussed. [Preview Abstract] |
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T1.00224: Non-linear DC response to an AC electric field for a two-band model Sergey Pershoguba Recently there has been rise of interest in various non-linear electromagnetic effects in solids. We calculate a second-order DC current response to an AC electric field for a generic two-band model with valence and conduction bands. The current is composed of two contributions: the intra- and interband terms. The intraband current occurs due to a resonant injection of the carriers to the conduction band. The current grows linearly with time as more carriers are excited into the conduction band until it is saturated by the relaxation processes. In contrast, the interband current is constant in time and occurs because of the interband hybridization of the valence and conduction bands. The interband current has both resonant and non-resonant components. The former component was previously referred to as the ``shift-current''. All expressions for the currents are composed of gauge-invariant combinations of Berry connections. We apply the results to specific tight-binding models. [Preview Abstract] |
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T1.00225: The decay of Hopf solitons in the Skyrme model David Foster In the 1960’s Skyrme proposed a topological model of atomic nuclei, where the solutions are lump-like and have an associated conserved topology. This topology stabilises them. The model’s energy functional can be understood as an elastic energy functional, and its minima correspond to nuclei. Recently the model has had success at replicating key properties of nuclei. Namely it has replicated the deuteron, diproton and dibaryon [1]. In the talk we will discuss knot-like solutions, which correspond to multiple nuclei anti-nuclei pairs. These solutions are not topologically stabilised, and can hence decay away. We see how different knots decay in different modes, which illuminates the local geometry of the configuration space. We will also discuss how certain knots/links life-time can be increased by a time dependent flow, leading to new nuclear physics predictions [2]. [1] D. Foster and N.S. Manton, Nuclear Physics B, 899 (2015) 513–526. [2] D. Foster `The decay of Hopf solitons in the Skyrme model' arXiv:1610.01571 (2016) [Preview Abstract] |
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T1.00226: Comparing association of preoperative transrectal ultrasound prostate weight with prostate weight obtained after radical prostatectomy after adjustment for other prognostic factors in a subset of the Northwestern University Prostate SPORE database. Irene Helenowski, Borko Jovanovic, Michael Gurley, Robin Leikin, William Catalona, Arden Roston, Timothy Kuzel Transrectal ultrasound (TRUS) is a non-invasive approach to measure prostate size as a surrogate (density$=$1.0) for prostate weight with implications in prostate cancer prognosis. But the question is how reliable is this preoperative measurement compared to other measures of prostate weight. This work presents the correlations between preoperative TRUS prostate weight and prostate weight obtained after radical prostatectomy in 434 patients with mean TRUS weight 36g (range: 10g-120g) and the mean prostate weight obtained after radical prostatectomy 51g (range: 16g-180g) from the Northwestern University Prostate SPORE database. 311 patients with weight obtained by digital rectal exam (DRE) were also compared to the TRUS prostate weights with mean and range of DRE weights 33g (10g -- 78g). Correlations were adjusted by age, BMI, an indicator variable for a pathological stage of III or greater, and for Gleason score greater than 7. Correlations were also computed for separately for European American and Other Race populations. Differences in means were evaluated via the paired t-test. Results indicate TRUS measures obtained via ultrasound as promising but improvement in the technology still appears needed. [Preview Abstract] |
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T1.00227: Counterfactual History is Consistent with Physics Charmayne Patterson, Ronald Mickens Counterfactual histories (CFHs) are histories that did not ``happen'' [1, 2]. For this concept to be meaningful, CFHs must correspond to states of the physical universe for which none of the laws of physics are violated. We present arguments to show that CFHs are realizable. Several of their critical features are: (i) their past states (histories) are uniquely determined from any given ``present state''; (ii) the future evolution from any given ``present state'' is non-predictable; and (iii) different trajectories, evolving from a given ``present state'' do not communicate with each other. We demonstrate the validity of these propositions by means of a toy universe that has these features. The general conclusion reached is that CFHs may exist. References: [1] ``The Counterfactual History Review'' ( research journal). [2] E. H. Carr, What is History (Cambridge University Press, 1961). [Preview Abstract] |
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T1.00228: Graduate students and Mental Health: what we know and what we can do Victor Schwartz There is scant but growing data about the mental health challenges and problems specific to graduate students. Nevertheless, the experience of graduate education can be extremely demanding and stressful and data suggest that graduate students are at higher risk for suicide than undergraduates and that when graduate students die by suicide it is more often related to academic stresses. This presentation will review what we know about the mental health of higher ed students in general and the growing body information about graduate student mental health. Finally, strategies that may be implemented to support the mental health of graduate students will be reviewed. [Preview Abstract] |
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T1.00229: Vacuum and vacuum force calculation Han Yongquan There is no vacuum in the universe, vacuum exists outside the universe, the universe is surrounded by a vacuum. Vacuum is dark matter, dark energy is an organic whole, is the same "thing" (vacuum) of the two properties - material properties, energy properties. Scientific calculations, dark matter, the percentage of dark energy is 96{\%}, it can be speculated that the vacuum should be now 24 times of the universe, that is, the final space can reach 25 times of the current space, reaching its maximum, so The size of the space (both vacuum and non-vacuum) is constant. Vacuum force calculation, the size of the vacuum force should be proportional to the size of the vacuum space, and proportional to the size of the non-vacuum density. Mathematical description: F $= \quad \delta \rho $v, where $\delta $ is proportional constant, $\rho $ is the density of non-vacuum, v is The size of the vacuum space. This explains that the universe is accelerating expansion, but the acceleration is smaller, also explains the dark energy is engulfing the dark matter to slow down the accelerate the expansion of the universe. Author: hanyongquan TEL: 15611860790 [Preview Abstract] |
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T1.00230: A Solution to the Band Gap and Related Problems in Density Functional Theory (DFT). Diola Bagayoko This presentation shows that the attainment of self-consistency, with a single basis set, does not allows one to reach results that possess the physical content of density functional theory (DFT). This fact is amply illustrated in the literature where reported DFT eigenvalues appear not to correspond to actual energy levels in materials under study. Our proof includes an understanding of the second Hohenberg-Kohn (HK) theorem that requires the use of successively larger and embedded basis sets to perform completely self-consistent calculations in order to reach the absolute minima of the occupied energies, i.e., the ground state of the system. Embedding here means that, except for the first one, each basis set is obtained by augmenting the one preceding it with one orbital. We also show that arbitrarily large basis sets, by virtue of the first HK theorem, are over-complete for the description of the ground state: This fact explains the well-known underestimation of energy and band gaps by single basis set calculations for the last 50 years. The non-attainment the ground state et the over-completeness of some large basis set explain the inaccuracy of calculated, optical transition energies, effective masses, dielectric functions and of a host of other computational results. [Preview Abstract] |
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T1.00231: DFT Predictions of Electronic, Transport, and Bulk Properties of Cubic Antifluorite A$_{\mathrm{\mathbf{2}}}${B Compounds (A}$=${ Li, Na, B}$=${ O,S,Se) } Yuriy Malozovsky, Lashounda Franklin, Diola Bagayoko We present results from \textit{ab-initio, }self-consistent calculations of electronic, transport, and bulk properties of cubic antifluorite (anti-CaF$_{\mathrm{2}})$ compounds A$_{\mathrm{2}}$B (A $=$ Li, Na, B $=$ O, S, Se). Our computations employed the local density approximation (LDA) potential of Ceperley and Alder and the linear combination of atomic orbital (LCAO) formalism. The implementation of the LCAO formalism followed the Bagayoko, Zhao, and Williams method, as enhanced by Ekuma and Franklin (BZW-EF). Consequently, our calculations search for and attained the ground states of the systems under study, as required by DFT; our results therefore possess the full, physical content of DFT. We discuss band structures, band gaps, and related properties of these materials, including calculated, total and partial densities of states (DOS and PDOS), effective masses of charge carriers, equilibrium lattice constants, and the bulk moduli of cubic antifluorite compounds A$_{\mathrm{2}}$B (A $=$ Li, Na, B $=$ O, S, Se). Our results are predictions in some cases, due to the lack of experimental data. [Preview Abstract] |
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T1.00232: It may be possible to Develop some very Exotic Energy Sources, like in a Sci-Fi Movie Richard Kriske This author previously put forward a theory, that he named "Kriske-Heaviside Field Theory". It is based on the idea that the EM Field developed from a changing Electric Field (in one observer's reference frame) is somewhat different than the EM Field generated from a change in a Static Magnetic field. This author proposed that if a Nuclear Field changed, or a Color Field or a Gravitational Field, that the change would in turn cause a "Circuitation" (a term from Heaviside) of one field then another, then another. For example a change in a Nuclear field could cause a change in a Magnetic Field (we see this in Nuclear Magnetic Resonance). Obviously in order to produce the Photon (which is an invariant, and a particle), the changing Magnetic field would have to change an Electric field. A final change could then be made to the Polarization of the Nuclear Field. So one could claim that a Circuit could be made (which one sees in an NMR). What about a changing Gravitational Field? There has been some writing that there is often lightning associated with an Earthquake, and there are many theories about static in sand, etc. Perhaps it is again "Ciruitation". If this is the case, all kinds of exotic devises could be made that have "Color" and "Gravity" as a part of a Circuit. [Preview Abstract] |
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T1.00233: The change law of the universe han yongquan The ideal gas state equation is not applicable to ordinary gas, it should be applied to the Electromagnetic "gas" that is applied to the radiation, the radiation should be the ultimate state of matter changes or initial state, the universe is filled with radiation. That is, the ideal gas equation of state is suitable for the Singular point and the universe. Maybe someone consider that, there is no vessel can accommodate radiation, it is because the Ordinary container is too small to accommodate, if the radius of your container is the distance that Light through an hour, would you still think it can't accommodates radiation? Modern scientific determinate that the radius of the universe now is about 10$^{\mathrm{27}}$ m, assuming that the universe is a sphere whose volume is approximately: V $=$ 4.19 × 10$^{\mathrm{81}}$ cubic meters, the temperature radiation of the universe (cosmic microwave background radiation temperature of the universe, should be the closest the average temperature of the universe) T $=$ 3.15k, radiation pressure P $=$ 5 × 10$^{\mathrm{-6}}$ N / m $^{\mathrm{2}}$, according to the law of ideal gas state equation, PV / T $=$ 6 × 10$^{\mathrm{75}}$, the value of this constant is the universe, The singular point should also equal to the constant [Preview Abstract] |
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T1.00234: A Perturbative Quantized Twist Embedded in Minkowski Spacetime. James Strohaber We present results on spatially-structured gravitational waves within the paraxial approximation. Drawing upon analogies between electrodynamics and general relativity, gauge invariant paraxial ``electric'' and ``magnetic'' parts of the Weyl conformal tensor are derived. In this approximation, a new gauge, which we call the paraxial-traceless gauge, is found. The polarization and degrees of freedom are investigated and compared with the Eardley-Newman-Penrose classification. Paraxial gravitational waves are found to share similarities with their electromagnetic counterparts in that they can possess a quantized amount of orbital angular momentum that can be transferred to matter. [Preview Abstract] |
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T1.00235: The Infinities in QED May Be Due to the Point: General Relativity May Provide the Resolution With Local Lorentz Frames 2 Douglas Snyder With regard to the infinities in quantum electrodynamics, most think the math is exact and the physics is approximate, but perhaps the physics is exact and the math is approximate. With a correct view of spacetime as comprised of local Lorentz frames which are the fundamental components of general relativity, we may have discrete units at the core of spacetime instead of infinitesimal points. General relativity may also provide the connection between electromagnetism and gravity since the establishment of spacetime in local Lorentz frames is founded on the motion of light (as seen in the relativity of simultaneity in different inertial reference frames in uniform translational motion relative to one another in special relativity). If correct, it is possible that the infinities in qed may be able to be eliminated without renormalization. [Preview Abstract] |
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T1.00236: Warped Space Optical Refraction William Webb When Loop Wave electrons and quarks rotate at relativistic speeds their circumferential length relativistically contracts (relativistically warps). Warpage causes the field near atoms to have contracted space dimensions. Space warpage is shown to produce a transparent material's optical refraction. Refraction is a natural consequence of Loop Wave relativistic space warpage. [Preview Abstract] |
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T1.00237: Characterization and structural properties of iron in plants. Udya Dewanamuni, Sunil Dehipawala, Harry Gafney Iron is one of the most abundant metals in the soil and occurs in a wide range of chemical forms. Humans receive iron through either meat products or plants. Non meat eaters depend on plant product for their daily iron requirement. The iron absorption by plants depends on other minerals present in the soil and soil pH value. The amount of iron present in plants grown with different soil compositions were investigated using X-ray absorption spectroscopy (XAS) and Mossbauer spectroscopy. Based on the X-ray absorption data, the amount of iron in plants vary significantly with soil pH value. The Mossbauer spectroscopy reveals that iron present in the samples has the form Fe$^{\mathrm{3+}}$ or electron density at the site of the iron nucleus similar to that of Fe$^{\mathrm{3+}}$. [Preview Abstract] |
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T1.00238: ``NON(!!!)-'SPOOKY'-ACTION(S)-at-(a)-NON(!!!)-Distance(S)'' AB INITIO/BY DEFINITION NON-``Mysterious'' AUTOMATIC(!!!)-but-NON(!!!)-(Artificial)-``ENTANGLEMENT(S'': Fourier(1822) VERSUS Einstein: WHY???: (k$=$1/r, w)-``Distance'' Does NOT(!!!) Exist!!! Edward Siegel ``NON(!!!)-Spooky [BOT\^{H}(!!!) CLASSICAL AND Q\^{U}ANTUM] Action at (\`{a}) NON(!!!)-Dist\"{a}nce(s)'' AB INITIO/BY DEFINITION(!!!) AUTOMATIC(!!!)-``ENTANGLEMENT'' NON(!!!)-``Paradox'': Hubbard[``?orld Ac\^{c}ording to Wavelets''(94)]: Fourier(1822)/Lapla\c{c}e(1865)/Melli\~{n}(1883)/Brillouin (31)/... DU\"{A}L/ INVERSE/INTEGR\"{A}L-TR\"{A}NSFORM (DT) (k$=$1/r,w$=$1/t)-Space ``DISPERSION-R\'{E}LATIONS!!!(DR): ``B\^{O}SON-ICS!!!'' ``TRUMPS''/VS. ``SPOOKY [ONLY(!!!)-Q\^{U}ANTUM-``ENTANGLEMENT''] Action at (a) [ONLY(!!!) in (r,t)-Space] Distance(s)''(SAAD) ``PARADOX'': EINSTEIN/EPR/BELL/...: \underline {\textbf{\textit{WHY???}}} ``Quantum-(and Classical!!!): 1822 \textless \textless \textless (CENTURY-EARLIER PRE-QUANTUM/PRE-CEDENCE!!!) \textless \textless \textless Schrodinger(22)/Heisenberg(27)/...: ``NON(!!!)-`SPOOKY' Action(s) at (a) NON(!!!)-Distance(s)'' \underline {\textbf{\textit{AUTOMATIC\"{A}LLY!!!}}} : ``GOD \underline {\textbf{\textit{D O E S}}} `THROW DICE'!!!'': Fourier/... DT (k$=$1/r,w$=$1/t)-Space DR(!!!) with AUTOMATIC(!!!) Parseval/Heisenberg ``UN-Certainty-Principle''(s) ZIPF-law infra-red divergence power-la? decay algbr\"{a}icity HYBERBOLICITY INEVITABILITY(!!!) power-spectrum VS (E/...) SAAD???: mere modern necromancy-practitioners' trendy media-hype P.R. spin-doctoring ``SHOW-BIZ!!!'', NOT ``bourgeo\^{\i}s'', BUT(Brooklyn vernacular purposely-irreverent ``raspberry'') ``Bush-WAAA-AAAH!''(\"{a}ka ``B.S.!!!'') [Preview Abstract] |
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T1.00239: Relativistic Masses vs. Absolute Masses Florentin Smarandache In the classical Twin Paradox, according to the Special Theory of Relativity, when the traveling twin blasts off from the Earth, his measuring stick and other physical objects in the direction of relative motion shrink to half their lengths. Similarly, the relativistic masses are considered as increasing when traveling at a relativistic speed. But if the object is rigid, doesn't it break? And, by the way, not all masses are variable, there exist absolute masses in the universe. [Preview Abstract] |
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T1.00240: Quantum Consciousness -- The Road to Reality Shantilal Goradia Per Einstein's theory mass tells space how to curve and space tells mass how to move. How do they “tell”? The question boils down to information created by quantum particles blinking ON and OFF analogous to 'Ying and Yang' or some more complex ways that may include dark matter. Consciousness, dark matter, quantum physics, uncertainty principle, constants of nature like strong coupling, fine structure constant, cosmological constant introduced by Einstein, information, gravitation etc. are fundamentally consequences of that ONE TOE. Vedic philosophers, who impressed Schrodinger so much, called it ATMA split in the categories of AnuAtma (particle soul), JivAtma (life soul) and ParamAtma (Omnipresent soul) which we relate to quantum physics, biology and cosmology. There is no separate TOE (Theory of Everything) for any one thing [1]. [1] Quantum Consciousness – The Road to Reality, Journal of Life Sciences 10 (2016) (doi: 10.17265/1934-7391/2016.06.001). [Preview Abstract] |
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T1.00241: Novel method to calculate inductance of arrays of wires Eric Deyo I show how to calculate the inductance of arrays of wires using complex analysis. [Preview Abstract] |
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T1.00242: POSTDEADLINE |
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T1.00243: A New Formalism for Quantifying Character of Vibrational Modes in Solids: Distinguishing Between Propagons, Diffusons and Locons Hamid Reza Seyf, Asegun Henry The solutions to the equations of motions for the atoms in homogenous crystalline solids result in plane wave modulated velocity fields for the normal modes of vibration. However, when a system lacks periodicity, either compositional or structural, the normal modes of vibration can still be determined, but the solutions take on different characters and many modes may be non-plane wave modulated. Previous work has classified the types of vibrations into three primary categories, namely propagons, diffusons and locons. Localized modes can be distinguished by calculation of participation ratio while distinguishing between propagons and diffusons is challenging because both are spatially delocalized. We present a new method that quantifies the extent to which a mode's character corresponds to a propagating mode, e.g., with a plane wave modulation. This then allows for clear and quantitative distinctions between propagons and diffusons. By resolving this issue quantitatively, one can now automate the classification of modes for any arbitrary structure subject to a single constraint that the atoms must vibrate stably around their respective equilibrium sites. [Preview Abstract] |
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T1.00244: Solute-solvent interactions and dynamics probed by THz light Gerhard Schwaab, Fabian B\"{o}hm, Chun-Yu Ma, Martina Havenith The THz range (1--12 THz, 30--400 cm$^{-1}$) is especially suited to probe changes in the solvent dynamics induced by solutes of different character (hydrophobic, hydrophilic, charged, neutral). In recent years we have investigated a large variety of such solutes and found characteristic spectral fingerprints for ions, but also for uncharged solutes, such as alcohols. We will present a status report on our current understanding of the observed spectral changes and how they relate to physico-chemical parameters like hydration shell size or the lifetime of an excited intermolecular oscillation. In addition, we will show, that in some cases the spectral changes are closely related to the partition function yielding access to a microscopic understanding of macroscopic thermodynamic functions. [Preview Abstract] |
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T1.00245: Analytic Critical Exponents at Strong Coupling Anthony Hegg A nonperturbative field theoretic method of generating renormalization group equations as applied to quartic strong coupling interactions is explored. Specifically, the correlation exponent and the anomalous dimension in the vicinity of a critical point are calculated via an expansion about the system size of a large but finite system. The results are analytic values which are compared to experiments via the usual scaling laws. [Preview Abstract] |
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T1.00246: Orbital-driven two-dome superconducting phases in iron-based superconductors LiangJian Zou, DaYong Liu, Feng Lu, Weihua Wang, H. Q. Lin Recent several experiments revealed that novel bipartite magnetic/superconducting phases widely exist in iron pnictides and chalcogenides. Nevertheless, the origin of the two-dome phases in iron-based compounds still remains unclear. Here we theoretically investigated the electronic structures, magnetic and superconducting properties of three representative iron-based systems, i.e. LaFeAsO1-xHx, LaFeAs1-xPxO and KFe2As2. We found that in addition to the degenerate anisotropic xz/yz orbitals, the quasi-degenerate isotropic orbitals drive these systems entering into the second parent phase. Moreover, the second superconducting phase is contributed by the isotropic orbitals rather than the anisotropic ones in the first superconducting phase, indicating an orbital-selective pairing state. These results imply an orbital-driven mechanism and shed light on the understanding of the two-dome magnetic/superconducting phases in iron-based compounds. [Preview Abstract] |
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T1.00247: Quasiparticle spin relaxation with superconducting-velocity--tunable state in GaAs (100) quantum wells in proximity to $s$-wave superconductor Tao Yu, M. W. Wu We investigate the quasiparticle spin relaxation with superconducting-velocity--tunable state in GaAs (100) quantum wells in proximity to $s$-wave superconductor. In the quasiparticle state, rich features such as the suppressed Cooper pairings, large quasiparticle density and non-monotonically tunable momentum current can be realized by varying the superconducting velocity. In the degenerate regime, the quasiparticle Fermi surface is composed by two arcs, referred to as Fermi arcs, which are contributed by the electron- and hole-like branches. The D'yakonov-Perel' spin relaxation is explored with intriguing physics revealed when the Fermi arc emerges. Specifically, when the order parameter tends to zero, the branch-mixing scattering is forbidden. The open structure of the Fermi arc leads to the nonzero angular-average of the effective magnetic field due to the spin-orbit coupling, acting as an effective Zeeman field. This Zeeman field leads to the spin oscillations even in the strong scattering regime. Moreover, in the strong scattering regime, the open structure of the Fermi arc leads to the insensitiveness of the spin relaxation to the momentum scattering, in contrast to the conventional motional narrowing situation. [Preview Abstract] |
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T1.00248: Topological Superconductivity on the Surface of Fe-Based Superconductors Gang Xu, Biao Lian, Peizhe Tang, Xiao-Liang Qi, Shou-Cheng Zhang As one of the simplest systems for realizing Majorana fermions, the topological superconductor plays an important role in both condensed matter physics and quantum computations. Based on \textit{ab initio} calculations and the analysis of an effective 8-band model with superconducting pairing, we demonstrate that the three-dimensional extended s-wave Fe-based superconductors such as Fe$_{\mathrm{1+y}}$Se$_{\mathrm{0.5}}$Te$_{\mathrm{0.5}}$ have a metallic topologically nontrivial band structure, and exhibit a normal-topological-normal superconductivity phase transition on the (001) surface by tuning the bulk carrier doping level. In the topological superconductivity (TSC) phase, a Majorana zero mode is trapped at the end of a magnetic vortex line. We further show that the surface TSC phase only exists up to a certain bulk pairing gap, and there is a normal topological phase transition driven by the temperature, which has not been discussed before. These results pave an effective way to realize the TSC and Majorana fermions in a large class of superconductors. [Preview Abstract] |
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T1.00249: A theory of nonequilibrium steady states in quantum chaotic systems Pei Wang Nonequilibrium steady state (NESS) is a quasistationary state, in which exist currents that continuously produce entropy, but the local observables are stationary everywhere. We propose a theory of NESS under the framework of quantum chaos. In an isolated quantum system, there exist some initial states for which the thermodynamic limit and the long-time limit are noncommutative. The density matrix $\hat \rho$ of these states displays a universal structure. Suppose that $\alpha$ and $\beta$ are different eigenstates of the Hamiltonian with energies $E_\alpha$ and $E_\beta$, respectively. $<{\alpha}|\hat \rho |{\beta}>$ behaves as a random number which approximately follows the Laplace distribution with zero mean. In thermodynamic limit, the variance of $<{\alpha}|\hat \rho |{\beta}>$ is a smooth function of $\left| E_\alpha-E_\beta\right|$, scaling as $1/\left| E_\alpha - E_\beta\right|^2$ in the limit $\left| E_\alpha-E_\beta\right|\to 0$. If and only if this scaling law is obeyed, the initial state evolves into NESS in the long time limit. We present numerical evidence of our hypothesis in a few chaotic models. Furthermore, we find that our hypothesis implies the eigenstate thermalization hypothesis (ETH) in a bipartite system. [Preview Abstract] |
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T1.00250: Entangled Bloch spheres: Bloch matrix and two-qubit state space Omar Gamel We represent a two-qubit density matrix in the basis of Pauli matrix tensor products, with the coefficients constituting a Bloch matrix, analogous to the single qubit Bloch vector. We find the quantum state positivity requirements on the Bloch matrix components, leading to three important inequalities, allowing us to parametrize and visualize the two-qubit state space. Applying the singular value decomposition naturally separates the degrees of freedom to local anr nonlocal, and simplifies the positivity inequalities. It also allows us to geometrically represent a state as two entangled Bloch spheres with superimposed correlation axes. It is shown that unitary transformations, local or nonlocal, have simple interpretations as axis rotations or mixing of certain degrees of freedom. The nonlocal unitary invariants of the state are then derived in terms of local unitary invariants. The positive partial transpose criterion for entanglement is generalized, and interpreted as a reflection, or a change of a single sign. The formalism is used to characterize maximally entangled states, and generalize two-qubit isotropic and Werner states. [Preview Abstract] |
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T1.00251: Numerical study on turbulent mixing of planar shock accelerated heavy triangular gases interface. Yutao Sun The interaction of a planar shock wave with a sulfur hexafluoride (SF6) triangular inhomogeneity surrounded by air is numerically studied based on high resolution finite volume method with Minimum Dispersion and Controllable Dissipation (MDCD) reconstruction. The vortex dynamics of Richtmyer-Meshkov instability (RMI) and the turbulent mixing during the evolution of Kelvin--Helmholtz instability (KHI) are well discussed. Several typical processes for shock driven inhomogeneity flow to become turbulent mixing transition are well demonstrated in this study. The spectral analysis of turbulent kinetic energy (TKE) shows that the merging process of the primary Kelvin--Helmholtz billows will extend the region with a broadband spectrum of motion, and consequently, enhance the overall mixing of fluids. Both analysis of the TKE spectra and the variable-density energy spectra manifests the inertial range by the latter stages. Additionally, length scales analysis shows that the Liepmann-Taylor scale is decoupled from the inner-viscous scale during the evolution, which implies that there is a turbulent mixing transition. A further analysis of energy transfer in Fourier space indicates the nonlinear transfer term is of significance while the physical dissipation term is negligible. The detailed analysis for the nonlinear transfer term implies that the quadratic and pressure components are dominant terms. [Preview Abstract] |
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T1.00252: Instability and turbulent mixing of shocked `V' shaped interface. Long Li, Yutao Sun Based on the mass fraction model of multicomponent mixture, the interaction between weak shock wave and `V' shaped air/ interface with different vertex angles are numerical simulated using high resolution finite volume method with minimized dispersion and controllable dissipation (MDCD) scheme. It is observed that the baroclinic vorticity is deposited near the interface due to the misalignment of the density and pressure gradient, leading to the formation of vortical structures along the interface. The predicted leftmost interface displacement and interface width growth rate in the early stage of interface evolution agree well with experimental results. The numerical results indicate that with the evolution of the interfacial vortical structures, the array of vortices begins to merge. As the result, the vortices accumulate at several distinct regions. It is in these regions, the multi-scale structures are generated because of the interaction between vortices. It is observed that due to the different scaling with Reynolds number of upper bound and lower bound, an uncoupled inertial range appears, and the mixing transition occurs with the appearance of an inertial range of scales. The classical Kolmogorov -5/3 power laws are shown in the energy fluctuation spectrum, which means the inertial range is just beginning to form and the flow field near the material interface will develop to turbulence. [Preview Abstract] |
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T1.00253: A cell-centered Lagrangian method based on local evolution Galerkin scheme for two-dimensional compressible flows. Li Tang, Yutao Sun The paper presents a new cell-centered Lagrangian method for two-dimensional compressible flows. The main feature of the method is that the velocity and pressure at the cell vertex are computed using the local Galerkin evolution scheme for solving the linearized flow equations in terms of the bicharacteristic theory, and then the velocity and pressure are used to update the grid coordinates and evaluate the numerical flux across the cell interface. The local Galerkin evolution operator in terms of the Lagrangian description is developed, which gives the solutions evolving for an infinite small time interval from the initial conditions and still maintaining the genuine multidimensional nature of hyperbolic system. Mean- while, the present method can preserve geometry compatibility. Several numerical results demonstrate that the method possesses of good property of convergence, symmetry and robustness, and has the ca pability to handle the multimaterial flows. [Preview Abstract] |
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T1.00254: Analysis of a Concentrated Solar Thermophotovoltaic System with Thermal Energy Storage Hamid Reza Seyf, Asegun Henry We analyzed a high temperature concentrated solar thermophotovoltaic (TPV) system with thermal energy storage (TES), which is enabled by the potential usage of liquid metal as a high temperature heat transfer fluid. The system concept combines the great advantages of TES with the potential for low cost and high performance derived from photovoltaic cells fabricated on reusable substrates, with a high reflectivity back reflector for photon recycling. The TES makes the electricity produced dispatchable, and thus the system studied should be compared to technologies such as concentrated solar power (CSP) with TES (e.g., using a turbine) or PV with electrochemical batteries, instead of direct and intermittent electricity generation from flat plate PV alone. Thus, the addition of TES places the system in a different class than has previously been considered and based on the model results, appears worthy of increased attention. The system level analysis presented identifies important cell level parameters that have the greatest impact on the overall system performance, and as a result can help to set the priorities for future TPV cell development. [Preview Abstract] |
(Author Not Attending)
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T1.00255: Landau-Zener transitions and Dykhne formula in a simple continuum model Yujin Dunham, Savannah Garmon The Landau-Zener model describing the interaction between two linearly driven discrete levels is useful in describing many simple dynamical systems; however, no system is completely isolated from the surrounding environment. Here we examine a generalizations of the original Landau-Zener model to study simple environmental influences. We consider a model in which one of the discrete levels is replaced with a energy continuum, in which we find that the survival probability for the initially occupied diabatic level is unaffected by the presence of the continuum. This result can be predicted by assuming that each step in the evolution for the diabatic state evolves independently according to the Landau-Zener formula, even in the continuum limit [1]. We also show that, at least for the simplest model, this result can also be predicted with the natural generalization of the Dykhne formula for open systems [2]. We also observe dissipation as the non-escape probability from the discrete levels is no longer equal to one. [1] A. Dodin, S. Garmon, L. Simine, and D. Segal, J. Chem. Phys. {\bf 140}, 124709 (2014). [2] A. M. Dykhne, Sov. Phys. JETP 14, 941 (1962). [Preview Abstract] |
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T1.00256: Finite-Size effects in the Optical and Magnetic Properties of MnCo$_{\mathrm{2}}$O$_{\mathrm{4}}$ Nanostructures Sobhit Singh, M. S. Seehra, P. Pramanik, S. Thota MnCo$_{\mathrm{2}}$O$_{\mathrm{4}}$ nanoparticles (NPs) find extensive applications in energy sectors such as in fuel cells, Li-ion batteries, supercapacitors, etc. Here we present a detailed study of the surface and finite size effects on the optical and magnetic properties of MnCo$_{\mathrm{2}}$O$_{\mathrm{4}}$ NPs synthesized by the sol-gel method. MnCo$_{\mathrm{2}}$O$_{\mathrm{4}}$ particles of various sizes (5.4 nm $\le $ d $\le $ 112 nm) were prepared by varying the heat treatment conditions of the oxalate precursor. The optical absorption spectra of these samples were recorded using a diffuse reflectance accessory. The optical bandgap (E$_{\mathrm{g}})$ values, determined using the Kubelka-Munk analysis, reveal a strong confinement induced blue shift, increasing E$_{\mathrm{g}}$ from 1.73 to 2.4 eV with decreasing size from 112 to 5.4 nm. Also, the role of crystallite size on the crystal field transitions e.g. ligand-to-metal (p-d at 3.10 eV) and intra-band metal-to-metal charge transfer transition (2.6 eV) within d-states has been analyzed. The ferrimagnetic ordering temperature (T$_{\mathrm{C}})$ determined from temperature dependence of dc-magnetic susceptibility $\chi $(T) measurements decreases to 140 K from the bulk value of 185 K with decreasing the crystallite size to 5.4 nm. Such size dependent variation of T$_{\mathrm{C}}$ follows the finite-size scaling relation T$_{\mathrm{C}}$(d) $=$ T$_{\mathrm{C}}(\infty )$[1-($\xi _{\mathrm{o}}$/d)$^{\mathrm{\lambda }}$, with shift exponent $\lambda $ $=$ 0.81 and microscopic correlation length $\xi_{\mathrm{o}} \quad =$ 1.48 nm that is almost twice the lattice parameter (8.27 {\AA}), confirming its microscopic nature. [Preview Abstract] |
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T1.00257: Effects of Cure Process Pathway on Toughened Thermoset Resin Topology and Morphology: A molecular dynamics study Carla Estridge During industrial processing of thermoset composite materials the epoxy resin systems experience numerous temperature and pressure profiles. Differences in the processing parameters may lead to differences in the ultimate performance of the material. In order to understand the molecular level origins of these differences in performance we have designed atomistic and coarse grained simulations that target understanding process induced variations in molecular level \textit{topology}, the polymeric network formation, and \textit{morphology}, the reaction induced phase separation of thermoset networks from thermoplastic toughening agents. We show how the cure path (ramp rate, hold temperatures and steps) has a significant impact on the molecular architecture of the resin systems and how we may use this information when designing process pathways for our thermoset composite materials. [Preview Abstract] |
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T1.00258: Multiscale Simulation of Polymeric Liquids with Heat Transportation Takahiro Murashima, Toshihiro Kawakatsu Polymeric liquids show complex flow behaviors coming from the complex microscopic molecular dynamics and structures. We usually assume a constitutive equation to represent a nonlinear relationship between strain and stress in polymeric liquids. In the multiscale simulation, we use a molecular dynamics simulation to describe the relationship between strain and stress at each fluid element instead of using the constitutive equation. The multiscale simulation consists of the macroscopic fluid particle simulation and the microscopic polymer dynamics simulation. The macroscopic fluid particle simulation represent the macroscopic flow of polymeric liquids and the microscopic polymer simulation represent the local dynamics of polymeric liquids. Since each polymer dynamics simulation is independent of the other simulators, the multiscale simulation is suitable for the massively parallel super computer. We have succeeded in describing the isothermal flow problem at the present framework. We develop the multiscale simulation framework to more general flow problem with heat transfer. In this talk, we use a dumbbell model as a microscopic simulator for the multiscale simulation. We discuss a heat transportation problem using the preliminary polymer model. [Preview Abstract] |
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T1.00259: Analysis of Thermo-Diffusive Cellular Instabilities in Continuum Combustion Fronts Hossein Azizi, Sebastian Gurevich, Nikolas Provatas We explore numerically the morphological patterns of thermo-diffusive instabilities in combustion fronts with a continuum solid fuel source, within a range of Lewis numbers, focusing on the cellular regime. Cellular and dendritic instabilities are found at low Lewis numbers. These are studied using a dynamic adaptive mesh refinement technique that allows very large computational domains, thus allowing us to reduce finite size effects that can affect or even preclude the emergence of these patterns. The distinct types of dynamics found in the vicinity of the critical Lewis number. These types of dynamics are classified as ``quasi-linear'' and characterized by low amplitude cells that may be strongly affected by the mode selection mechanism and growth prescribed by the linear theory. Below this range of Lewis number, highly non-linear effects become prominent and large amplitude, complex cellular and {\it{seaweed}} dendritic morphologies emerge. The cellular patterns simulated in this work are similar to those observed in experiments of flame propagation over a bed of nano-aluminum powder burning with a counter-flowing oxidizer conducted by Malchi et a{\it{l}}. It is noteworthy that the physical dimension of our computational domain is roughly close to their experimental setup. [Preview Abstract] |
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T1.00260: Nodeless and Topological Superconductivity of Doped Mott insulator in Proximity to Antiferromagnets Guo-Yi Zhu, Ziqiang Wang, Guang-Ming Zhang Motivated by the recent experimental observations of nodeless superconductivity in high-Tc copper oxides, we investigate the proximity effect of anti-ferromagnets adjacent to doped Mott insulator. By performing slave Boson mean-field treatment to t-J model with external staggered magnetic field, we identified the evolution of the pairing symmetries from d-wave to s-wave with growing staggered magnetization. Even more, we found transition from nodal to nodeless d-wave when Fermi-surface is suppressed by staggered magnetization, and the same mechanism also applies to transition from nodal to nodeless s-wave phase. At the intermediate regime between pure d-wave and s-wave, the system is dominated by s+id pairing symmetry instead, which is also divided into two phases (s+id)w for weak pairing and (s+id)s for strong pairing, depending on the presence of Fermi-surface. What's more interesting is that the (s+id)w phase with Fermi-surface is topologically nontrivial and shows robust gapless edge modes protected by valley symmetry. These findings strongly suggest that doped Mott insulator in proximity to anti-ferromagnets can produce fully gapped superconductivity with various pairing symmetries and potentially realize the topological valley superconductor. [Preview Abstract] |
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T1.00261: Temperature-dependent electron transport mechanism in CS/PEO and CS/PANiES composites. Cesar Nieves, Luis Martinez, Idalia Ramos, Anamaris Melendez, Natalya Zimbovskaya, Margarita Ortiz, Nicholas Pinto Carbon spheres (CS) were prepared via hydrothermal method using an aqueous solution of sucrose and heated at 400C. The spheres were thermally annealed in N$_{\mathrm{2}}$ at 800C to increase the conductivity due the elimination of functional groups on the surface of the CS. Electron transport as function of temperature was studied using an insulating (polyethylene oxide-PEO) and a conducting (polyaniline-PANiES) polymer. Electrical characterizations of the composites were carry out showing Ohmic current-voltage response and temperature-dependent conductivity in the range of 80K to 300 K. The dependence of conductivity on temperature was theoretically analyzed to determine predominating mechanisms of electron transport. A conductivity maxima at 258K was observed in the CS/PEO composite but was absent in the CS/PANiES composite. While thermally induced-tunneling and thermal activation are responsible for electron transport in CS/PEO, variable range hopping (VRH), thermally induced-tunneling, and thermal activation are responsible for electron transport in CS/PANiES composite. [Preview Abstract] |
(Author Not Attending)
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T1.00262: A Study of Fundamental Law of Thermal Radiation and Thermal Equilibrium Process Chen Dayou The fundamental law of thermal equilibrium radiation includes two elements: the law of energy distribution of matter vibrators in the radiation field and the law of energy exchange between vibrators and the radiation field. This paper discovers the law of how vibrators stimulate and absorb radiation, by a study of the black-body radiation law and the characteristics of vibrators' absorption of radiation. As for the fundamental law of thermal equilibrium radiation, its complete expression should be: the energy distribution of vibrators in the thermal equilibrium radiation field follows the energy distribution law by L. Boltzmann; the probability of vibrators' stimulating radiation is directly proportional to their state of energy levels and that of their absorbing radiation is directly proportional to their energy distribution probability. The author, on the basis of the fundamental law of thermal radiation, proposes conditions for thermal equilibrium radiation and analyses the micro momentum theory and characteristics in the process of thermal equilibrium. [Preview Abstract] |
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T1.00263: A Computational Study of Time-resolved Resonant Inelastic X-ray Scattering Yuan Chen, Yao Wang, Brian Moritz, Thomas Devereaux Resonant inelastic X-ray scattering (RIXS) is a spectroscopic technique widely used in the characterization of elementary excitations including charge, magnetic, and orbital degrees of freedom. With growing time resolution, these X-ray sources paved the way for time-resolved experiments, which provide a powerful tool to track the evolution of intertwined orders based on the information extracted from elementary excitations. To take advantage of RIXS in ultrafast dynamics, we perform the calculations of time-resolved nonequilibrium RIXS in a pump-probe process. The pump-induced resonance effects in the particle-hole continuum reflect the connection to incident energy, while the modulation of dispersions indicate the change of underlying interactions out of equilibrium. Due to the rich information obtained from trRIXS, this study provides a theoretical understanding of the change of various elementary excitations and their interplay with electrons in a pump-probe experiment. [Preview Abstract] |
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T1.00264: Reconstitution radicicol containing apolipoprotein B lipoparticle and tracing its cell uptake process by super resolution fluorescent microscopy. Chung Ching Lin, Po-Yen Lin, Chia-Ching Chang Apolipoprotein B (apoB) is the only protein of LDL. LDL delivers cholesterol, triacylglycerides and lipids to the target cells. Reconstitute apoB lipoparticle (rABL) will be an idea drug delivery vehicle for hydrophobic and amphiphilic materials delivery. It is challenged to renature ApoB into its functional state from denatured state. By using modified bile salt and radicicol (Rad) added over-critical refolding process, apoB can be restored into its native like state. The intrinsic fluorescence of apoB increased during the refolding process. Moreover, radicicol (Rad) molecules have been encapsulated into reconstitute rABL (Rad@rABL). To investigate the cell uptake mechanism of Rad@rABL, a super resolution ground state depletion (GSD) microscopy is used in this research. Fluorescence labeled Rad@rABL can be traced within the tumor cell. [Preview Abstract] |
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T1.00265: Gate-driven pure spin current in graphene Xiaoyang Lin, Li Su, Youguang Zhang, Arnaud Bournel, Yue Zhang, Jacques-olivier Klein, Weisheng Zhao, Albert Fert An important challenge of spin current based devices is to realize long-distance transport and efficient manipulation of pure spin current without frequent spin-charge conversions. Here, the mechanism of gate-driven pure spin current in graphene is presented. Such a mechanism relies on the electrical gating of conductivity and spin diffusion length in graphene. The gate-driven feature is adopted to realize the pure spin current demultiplexing operation, which enables gate-controllable distribution of the pure spin current into graphene branches. Compared with Elliot-Yafet spin relaxation mechanism, D'yakonov-Perel spin relaxation mechanism results in more appreciable demultiplexing performance, which also implies a feasible strategy to characterize the spin relaxation mechanisms. The unique feature of the pure spin current demultiplexing operation would pave a way for ultra-low power spin logic beyond CMOS. [1] L. Su, X. Lin, W. Zhao, A. Fert, et al., arXiv:1608.05132. [Preview Abstract] |
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T1.00266: Physical Algebra Kay C Erb A constructive algebra of physical units, physical algebra, is introduced with its application to fundamental physics and relativistic mechanics. The rules of this algebra are analogous to Euclidean constructions where the generalized concept of a unit and inverse unit are the fundamental elements of the geometry and the algebra. The units and inverse units are shown to be orthogonal and inverse subspaces of the algebra and have many ties to geometric algebra. In fact, physical algebra is an extension of geometric algebra over the field of hyperreal numbers, where physical units are elements of the ring. Though physical algebra is far from complete, some early implications and applications are explored in this presentation. In particular, it can be shown that the products of fundamental units representing space and time form orthogonal and inverse vector subspaces that correspond to light-like and mass-like physical subspaces. This framework applied to the QED picture of electrons and photons suggests a neutral concept, an entity that can be projected into light-like and mass-like frames and has components in both. As applied to relativity, these projections are consistent with and may be useful pedagogically to understanding the underlying geometry of spacetime. [Preview Abstract] |
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T1.00267: Quantum algorithms for optimisation problems in machine learning Maria Schuld, Patrick Rebentrost, Seth Lloyd, Ilya Sinayskiy, Francesco Petruccione In the emerging discipline of quantum-enhanced machine learning, quantum computing is applied to machine learning tasks in order to improve the complexity, performance or robustness of the learning algorithms. In most cases the approach is to translate the training procedure into an optimisation problem which can be tackled by means of quantum information processing. Here we present two quantum algorithms that follow such an approach. The first one uses quantum techniques for density matrix exponentiation and matrix inversion for least-squares optimisation in linear regression. The second method considers the much more difficult realm of non-convex optimisation and proposes a quantum algorithm for gradient descent and Newton's method, with special application to optimisation of homogeneous polynomials. In the best case, both quantum algorithms have a logarithmic dependency on the dimensions of the dataset which makes them particularly interesting for big data applications. [Preview Abstract] |
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T1.00268: Porous electrode swelling: effects of inhomogeneity and geometry Xuewei Zhang The performance and reliability of electrochemical devices can be significantly influenced by the changes in volume and porosity of the electrodes. Mathematical models have been developed over the last decade to describe and predict the dynamics of porous electrode expansion coupled with porosity change. Based on previous works, here we examine the effects of spatial inhomogeneity of electrode material on the model simulation results. Further, we extend our investigation from planar to cylindrical geometry and compare the electrode behavior in these two settings. [Preview Abstract] |
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T1.00269: Are Metallic Glasses Stronger or Tougher than Their Crystalline Alloy Counterparts at the Nanoscale? Jingui Yu, Mingchao Wang, Shangchao Lin Brittle failure in metallic glasses (MGs), which restricts their wide commercial applications, has been largely unexplored their inherently microstructural evolution at the atomistic level. Herein, we predict the influence of aspect ratios and compositions on the mechanical properties of nanoscale Cu$_{x}$Zr$_{\mathrm{100-}}_{x}$ MGs and their crystalline counterparts using molecular dynamics (MD) simulations. We find that aspect ratio has a key role in the brittle-to-ductile transition (BDT) in MGs. From low to high aspect ratios, we attribute such BDT behavior primarily to the increasing number of small pieces of shear band and the slower reformation capability of icosahedra. In contrast, the Cu$_{x}$Zr$_{\mathrm{100-}}_{x}$ crystal shows a composition-dependent BDT, that is, higher Cu content exhibits better ductility. Furthermore, unlike the failure mechanism of MGs, Cu$_{\mathrm{75}}$Zr$_{\mathrm{25}}$ and Cu$_{\mathrm{50}}$Zr$_{\mathrm{50}}$ crystals exhibit superplasticity and typical plasticity due to twinning and dislocation, respectively. As an outlier, Cu$_{\mathrm{25}}$Zr$_{\mathrm{75\thinspace }}$crystal exhibits a brittle behavior due to continuous voids ahead of the crack tip. More interestingly, the yield strength of single crystal is larger than that of MGs with the same aspect ratio due to the scarcity and low mobility of dislocations, coupled with constraint from tensile surface stresses. We observe weak size dependence in MGs, but very strong size dependence in single crystals, which leads to an exciting dimensional yield-stress crossover at \textasciitilde 300 $\mu $m. This study provides fundamental guidance for the optimal design of MGs and single crystalline structural materials with high strength and ductility. [Preview Abstract] |
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T1.00270: Deep strong coupling in a circuit QED system - huge Lamb shift - Tomoko Fuse, Fumiki Yoshihara, Sahel Ashhab, Kouichi Semba Among a variety of cavity/circuit-QED systems, circuits employing superconducting flux qubits as artificial atoms can achieve large coupling strengths because of the flux qubit's huge magnetic moment [1-3]. Using a flux qubit and a compact superconducting LC oscillator, we have realized so-called deep strong coupling between the qubit and the oscillator, where $g / \omega_o/ 2\pi = 1.3$ ($g$: coupling strength, $\omega_o/ 2\pi $: bare oscillator frequency) [1]. The measured spectra of the coupled system are well described with the Hamiltonian of Rabi model. The bare qubit frequency $\Delta / 2\pi $ is found to be ~3.8 GHz, and the theoretical model predicts that the frequency of the qubit, $\omega_{01}$, will be suppressed to ~0.5 GHz, indicating an extraordinary large Lamb shift of about 0.85$\Delta $. Recently, we have measured the spectrum of $\omega_{01}/ 2\pi $, by driving $\omega_{01}/ 2\pi $ and probing $\omega_{03}/ 2\pi $. In this presentation, the measured spectroscopy data will be shown. [1] F. Yoshihara, T. Fuse, et al., Nature Physics (2016) doi:10.1038/nphys3906. [2] P. Forn-Diaz, et al., Nature Physics (2016) doi:10.1038/nphys3905. [3] S. Ashhab and F. Nori, PRA 81, 042311 (2010). [Preview Abstract] |
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T1.00271: First principles study of Atomic Force Microscope manipulation of Ag atom on Si(111)-(7x7) surface. Batnyam Enkhtaivan, Atshushi Oshiyama We report on our total-energy electronic-structure calculations based on the density-functional theory that clarify atom-scale mechanisms of atom-manipulation recently realized on Si(111)-(7x7) surface at room temperature [1]. We focus on Ag adatom diffusion between the half unit cells (HUC) of Si(111)-(7x7), and identify reaction pathways and corresponding reaction energy barriers. We have found three different reaction pathways. Without the presence of the AFM tip, the rate determining barrier is 0.8 eV. We consider the manipulation by the Si and Pt tips. When the tip-surface distance is 3.5 angstrom, due to the interaction between the tip and the diffusing adatom, the reaction barrier is reduced to about 0.25 eV and 0.60 eV by Si and Pt tips, respectively. We find that the reduction of the barrier depends on the flexibility of the tip apex structure. The tip apex adatom of Si tip moves about 0.86 angstrom toward Ag adatom to form bond, while that of Pt tip does not move. The tip not only reduces the diffusion barrier, but also traps the adatom under it. We find that the shape of the tip apex is important. When the adatom interacts with multiple tip atoms, the adatom is strongly trapped. [1] Y. Sugimoto et al., Nat. Commun. 5, 4360 (2014). [Preview Abstract] |
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T1.00272: Convective penetration in stars Jane Pratt, Isabelle Baraffe, Tom Goffrey, Tom Constantino, M.V. Popov, Rolf Walder, Doris Folini To interpret the high-quality data produced from recent space-missions it is necessary to study convection under realistic stellar conditions. We describe the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code MUSIC, currently being developed at the University of Exeter. We use MUSIC to study convection during an early stage in the evolution of our sun where the convection zone covers approximately half of the solar radius. This model of the young sun possesses a realistic stratification in density, temperature, and luminosity. We approach convection in a stellar context using extreme value theory and derive a new model for convective penetration, targeted for one-dimensional stellar evolution calculations. [Preview Abstract] |
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T1.00273: Discharge reaction mechanism in SnS anode for Na-ion batteries: First-principles calculations Hiroki Kotaka, Hiroyoshi Momida, Tamio Oguchi Li-ion batteries have been widely used as power sources in modern electronics devices because of its high energy densities and high voltages. However typical Li-ion batteries are relatively expensive, because electrode materials contain high-cost rare-metals such as Li and Co. To solve the cost problem, Na-ion batteries have been recently expected as a next-generation rechargeable battery in which high-cost Li is replaced with low-cost Na. As an anode material suitable for Na-ion batteries, beta-Sn is known to show a high energy density, but one problem of Sn anode is very large volume changes during charge and discharge processes. In this study, we focus attention on tin sulfide (SnS) as a candidate anode material for Na-ion batteries. We perform structural searches of possible reaction products during discharge reaction processes, and theoretically find the discharge reaction formulae for the Na-SnS half-cell by using the first-principles calculations. We show the electrochemical properties such as voltage-capacity curves, and compare our calculated results with the experiments. We also show calculation results of x-ray absorption spectra, and discuss the experimentally reported spectral changes during discharging. [Preview Abstract] |
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T1.00274: Fabrication of Diamond for Low Temperature Experiments Li He, Wenqian Lian, Xinxing Yuan, Huili Zhang, Chuheng Zhang, Xiuying Chang, Panyu Hou, Wengang Zhang, Xin Wang, Xiaolong Ouyang, Xianzhi Huang, Luming Duan The nitrogen-vacancy (NV) center in diamond is a promising physical implementation of quantum computing. At low temperature (about 4K), NV center shows a lot of advantages comparing with room temperature. The coherence time of electron spin in NV center is 10 ms. Besides, the electron spin state read out efficiency is increased by single shot read out. Most importantly, the electron spin can be resonantly drived, so remote NV centers can be entangled by the interference of the resonant zero phonon line photons, which is a promising scheme for the realization of quantum computer based on NV center. Here we show the fabrication work on diamond and the basic test at the low temperature toward quantum network based on NV center. We fabricate solid immersion lens (sil) on the top of located NV centers and get the enhancement of fluorescence collection efficiency by a factor of 8. Metal structures are deposited beside the sil to transport microwave and RF signal for the manipulation of electron spin and nuclear spin. We also show the resonant optical spectrum of NV center with and without microwave applying. [Preview Abstract] |
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T1.00275: Investigation of Atmospheric Aerosol properties by Atomic Force Microscopy Barry Sevalia, Kelli Joseph, Morewell Gasseller The effects of aerosols on the atmosphere, climate, and public health are among the central topics in current environmental research. Aerosol particles scatter and absorb solar and terrestrial radiation, they are involved in the formation of clouds and precipitation as cloud condensation and ice nuclei, and they affect the abundance and distribution of atmospheric trace gases by chemical reactions and other multiphase processes. Moreover, airborne particles play an important role in the spreading of biological organisms, reproductive materials, and pathogens and they can cause or enhance respiratory, cardiovascular, infectious, and allergic diseases. In this study we use two distinct methods to characterize atmospheric aerosol particles. With the AFM, we use analytical and interpretative techniques to deduce fundamental physical properties of the aerosol particles such as particle sizes and morphology. The microscopy techniques are then compared and complemented with optical techniques that employ hand held sun photometers to measure aerosol optical thickness (AOT) of the atmosphere. The chemical nature of the aerosols is investigated by exposing the samples to a stream of ozone gas and then reimage them. Using this approach, we are only able to classify particles as organic, gr [Preview Abstract] |
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T1.00276: Realization of controllable photonic molecule based on three ultrahigh-Q microtoroid cavities Chao Yang, Xiaoshun Jiang, Qian Hua, Shiyue Hua, Jiyang Ma, Yuan Chen, Min Xiao Three-cavity photonic molecules have been realized in several platforms, but their structures and configurations are mostly fixed with limited tunability in the coupling strengths and individual resonant frequencies. Here, we demonstrate an experimental realization of a coupled triple-cavity photonic molecule (TCPM) composed of three independently-selectable ultrahigh quality microtoroids. By precisely tuning the inter-cavity coupling strengths (via distances) and the resonant frequencies (via fine temperature control), as well as coupling the tapered optical fiber onto either the side or middle cavity, evolutions of the TCPM’s supermodes are fully mapped and analyzed. Interesting phenomena, such as dark state and double anti-crossing, emerge in this TCPM system. When the quality factors of the cavities are properly chosen, transition from double electromagnetically-induced transparency to double electromagnetically-induced absorption phenomena happens. Such fully-controlled TCPM system sets a stage for future investigations of new physical effects including cavity-QED with multiple coupled cavities and topologically protected photonic states. [Preview Abstract] |
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T1.00277: Evidence for Layered Quantized Transport in Topological Insulator ZrTe$_{\mathrm{5}}$ Wei Wang, Xiaoqian ZHang, Liang He ZrTe$_{\mathrm{5}}$ is an important semiconductor thermoelectric material and a candidate topological insulator. Here we report observation of Shubnikov-de Hass oscillations accompanied by quantized Hall resistance in ZrTe$_{\mathrm{5}}$ crystal, and the mobility can achieve 41000 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$. The angle-depended magnetoresistance demonstrates that the transport properties are 2D-like. We also founded that Hall conductance $G_{\mathrm{xy}}$ shows quantized step and each step is 1 $e^{\mathrm{2}}$/$h$ for single layer. We provide the Shubnikov-de Hass oscillations do not origin form the surface states, but come from the bulk. Each single layer ZrTe$_{\mathrm{5}}$ act like an independent 2D electron systems, and the bulk of the sample shows a multilayered quantum Hall effect. In addition to reveal the nature of Shubnikov-de Hass oscillations, we also provide a new point to explain the anomalous peak nature in temperature resistance, which have puzzled many years for the scientists. [Preview Abstract] |
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T1.00278: Evolution of crystallization and magnetic phase transition in Cu1-xZnxFe2O4 studied by neutron powder diffraction. Fenfen Chang, Maxim Avdeev, Guochu Deng, James Hester, Xiaolin Wang, Clemens Ulrich High resolution and high intensity neutron powder diffraction were applied to study the crystallographic and magnetic phase transition in Cu1-xZnxFe2O4 from 4 K to 750 K. Structural phase transition from cubic to tetragonal phase was observed in CuFe2O4. Ferrimagnetic order was observed in CuFe2O4 and short-range antiferromagnetic scattering was observed below 10 K in cubic ZnFe2O4 which is strongly restrained by addition of slightly amount of Cu2$+$ ions. Upon doping, ferromagnetic order temperature was gradually reduced from 789 K. Collinear spin setting was observed and no indication of frustration was found even up to doping rate of x $=$ 0.6. Highly frustrated Cu0.04Zn0.96Fe2O4 and ZnFe2O4 behave short-range antiferromagnetic order, induced by the competing between ferromagnetic interaction from first-nearest neighbor and antiferromagnetic interaction from the third-nearest neighbor in tetrahedron formed by Fe ions on B sites. [Preview Abstract] |
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T1.00279: New Technique for Fabrication of Scanning Single-Electron Transistor Microscopy Tips Eric Goodwin, Stuart Tessmer Fabrication of glass tips for Scanning Single-Electron Transistor Microscopy (SSETM) can be expensive, time consuming, and inconsistent. Various techniques have been tried, with varying levels of success in regards to cost and reproducibility. The main requirement for SSETM tips is to have a sharp tip ending in a micron-scale flat face to allow for deposition of a quantum dot. Drawing inspiration from methods used to create tips from optical fibers for Near-Field Scanning Optical Microscopes, our group has come up with a quick and cost effective process for creating SSETM tips. By utilizing hydrofluoric acid to etch the tips and oleic acid to guide the etch profile, optical fiber tips with appropriate shaping can be rapidly prepared. Once etched, electric leads are thermally evaporated onto each side of the tip, while an aluminum quantum dot is evaporated onto the face. Preliminary results using various metals, oxide layers, and lead thicknesses have proven promising. [Preview Abstract] |
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T1.00280: High Throughput Fluorescence-based Force Spectroscopy of Single Molecule Interactions with DNA Origami Nano-springs Randy Patton, Carlos Castro Biological movement and processes are ultimately driven by the interactions of singular biomolecules. However, only in the past few decades have techniques and been developed capable of probing these interactions at single molecule resolutions. The focus of this work is the development, characterization, validation, and application of a nanoscale device designed explicitly for fluorescence-based single molecule force spectroscopy, mimicking the function of traditional techniques at the nanoscale. The nanostructure comprises a stiff platform with attachment points for two biomolecules (a receptor and a ligand), a flexible single DNA linker that acts as an entropic spring, and fluorescent molecules to facilitate readout of the binding interaction via a FRET interaction. This device will enable the investigation of the kinetics and mechanical stability of biomolecular interactions and singular biomolecules in a highly parallel fashion. We have constructed the device and performed proof of principle experiments probing DNA base-pairing interactions. [Preview Abstract] |
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T1.00281: Evidence of Intertube Excitons Observed in the Raman Resonance Excitation Profiles of $(6,5)$-Enriched SWCNT Bundles J. R. Simpson, A. R. Hight Walker, O. Roslyak, E. Haroz, H. Telg, J. G. Duque, J. J. Crochet, A. Piryatinkski, S. K. Doorn Understanding the photophysics of exciton behavior in single wall carbon nanotube (SWCNT) bundles remains important for opto-electronic device applications. We report resonance Raman spectroscopy (RRS) measurements on $(6,5)$-enriched SWCNTs, dispersed in aqueous solutions and separated using density gradient ultracentrifugation into fractions of increasing bundle size. Near-IR to UV absorption spectroscopy demonstrates a redshift and broadening of the main excitonic transitions with bundling. A continuously tunable dye laser coupled to a triple-grating spectrometer affords measurement of Raman resonance excitation profiles (REPs) over a range of wavelengths, (505 to 585)\,nm, covering the $(6,5)$-$E_{22}^S$ excitation. REPs of both the radial breathing mode (RBM) and G$_{\mathrm{LO}}^+$ reveal a redshifting and broadening of the $(6,5)\ E_{22}^S$ transition energy with increasing bundle size. Most interestingly, we observe an additional peak in both the RBM and G$_{\mathrm{LO}}^+$ REPs of bundled SWCNTs, which is shifted lower in energy than the main $E_{22}^S$ and is anomalously narrow. We attribute this additional peak to a transverse, intertube exciton. [Preview Abstract] |
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T1.00282: Turning Passive Brownian Motion Into Active Motion Francisco J Sevilla, Alejandro Vásquez-Arzola, Enrique Puga-Cital We consider out-of-equilibrium phenomena, specifically, the pattern of motion of active particles. These particles absorb energy from the environment and transform it into self-locomotion, generally, through complex mechanisms. Though the out-of-equilibrium nature of on the motion of these systems is well recognized, is generally difficult to pinpoint how far from equilibrium these systems are. In this work we elucidate the out-of-equilibrium nature of non-interacting, trapped, active particles, whose pattern of motion is described by a run-and-tumble dynamics. We show that the stationary distributions of these run-and-tumble particles, moving under the effects of an external potential, is equivalent to the stationary distribution of non-interacting, passive Brownian particles moving in the same potential but in an inhomogeneous source of heat. The interest in this topic has recently regrown due to the experimental possibility to design man-made active particles that emulate the ones that exist in the biological realm. [Preview Abstract] |
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T1.00283: Abstract Withdrawn
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T1.00284: Quantum State Transfer Between Valley and Photon Qubits Ming-Jay Yang, Yu-Shu Wu, Han-Ying Peng, Neil Na Quantum state transfer (QST) between valley and photon qubit is presented for the application of quantum communication. This QST is analogous to spin-photon QST [1], and is based on the electron-photon interaction in 2D hexagonal materials that obeys an unique optical transition selection rule, the “electron valley -- photon polarization” correspondence [2]. A generic proposal involving two optical cavities is introduced. The incoming photon carrying quantum information in its polarization enters the first cavity to interact and become entangled with the valley qubit. It is then followed by a measurement performed on the polarization of the photon exiting the second cavity to un-entangle the both qubits and transfer the information to the valley qubit. A quantum-mechanical wave equation-based analysis is performed, and analytical expressions are derived for the two important figures of merits that characterize the transfer, yield and fidelity. In conclusion, the study suggests that the unique valley-polarization correspondence in 2D hexagonal materials can be exploited to achieve valley-photon QST with promising yield and high fidelity.[1] H. Kosaka et al., Phys. Rev. Lett. 100, 096602 (2008).~[2] G. Y. Wu et al., Phys. Rev. B 86, 045456 (2012). [Preview Abstract] |
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T1.00285: Lithiation-Assisted Strengthening Effect and Reactive Flow in Bulk and Nano-Confined Sulfur Cathodes of Lithium-Sulfur Batteries Mingchao Wang, Jingui Yu, Shangchao Lin Sulfur (S) serves as a promising cathode material in Li-ion batteries owing to its abundance on earth, low cost and high theoretical specific capacity \textasciitilde 1670 mAhg-1, which is 3-5 times higher than that of current commercial Li-ion batteries. Nowadays, the most popular strategies of using S cathode are based on producing nanostructured carbon matrices (i.e. hollow carbon nanospheres and nanofibers) to sustain S cathode loading. However, the possible stress evolution and mechanical degradation of the confined S cathode in those carbon matrices have never been explored before. In addition, the associated structural and conductivity changes of the confined S cathode during the lithiation/delithiation process plays a significant role in the battery performance. With the above in mind, here we conduct reactive molecular dynamics simulations to investigate the microstructural and stress evolution of the confined S cathode during lithiation/delithiation process. Simulation results indicate an unusual stress relaxation state in Li$_{\mathrm{x}}$S compounds at lower Li concentrations (x \textgreater 0.7). The strength of corresponding Li-S compounds also increases with respect to the Li concentration. [Preview Abstract] |
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T1.00286: Supersolid with Emergent SU(2) Symmetry Simon Lieu, Andrew Ho, Derek Lee, Piers Coleman We present a model of a supersolid on a 2D triangular lattice with non-Abelian ground-state symmetry generators and examine the low-energy behavior using Bogoliubov theory. A mean-field phase diagram is found in terms of interaction parameters of the model and a region with an emergent SU(2) symmetry is identified at a phase boundary between a time-reversal (TR) symmetric and TR-broken supersolid. The enlarged degeneracy manifests itself via the acquisition of a quadratic Goldstone mode and the topological instability of global phase vortices. This latter point implies that such a supersolid is not expected to undergo a BKT superfluid transition. The zero-temperature superfluid fraction is calculated using linear response. [Preview Abstract] |
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T1.00287: Demystifying the Expert Anca Constantin, Klebert Feitosa We present here a program that aims at significantly diminishing the increasingly pervasive fear of approaching scientific concepts, particularly for people without math related backgrounds or interests. We built a series of grassroots yet unique science shows delivered in an up-beat, visually, and socially appealing environment, that bring forward the crucially needed bridge between the realm of scientific research and that of ordinary people through... comedy. While staged by two physics professors as hosts, the hilarious interactions between a science expert and a student-led improvisational comedy troupe constitute the main tool to unlock, decipher, and enjoy the mystery of the scientific research. Our program gets everyone in with lots of laughs, at no expense to academic quality, community involvement, diversity, excellence, integrity, and student focus. Our independent dedicated website for this project (sites.jmu.edu/demystifying), archives the podcasts (soundcloud.com/demystifying), short segment videos, blog posts, experts’ bios, photo albums, testimonials, press releases, along with quantitative results of our assessment efforts. The overarching goal of this program is to pioneer a low cost yet efficient method of science education that can be replicated world wide. [Preview Abstract] |
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T1.00288: Free-electron Creation at the 60° Twin Boundary in Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ Seung-Hyub Baek, Kwang-Chon Kim, Jin-Sang Kim Interfaces, such as grain boundaries in a solid material, are excellent regions to explore novel properties that emerge as the result of local symmetry-breaking. For instance, at the interface of a layered-chalcogenide material, the potential reconfiguration of the atoms at the boundaries can lead to a significant modification of the electronic properties because of their complex atomic bonding structure. Here, we report the experimental observation of an electron source at 60° twin boundaries in Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$, a representative layered-chalcogenide material. First-principles calculations reveal that the modification of the interatomic distance at the 60° twin boundary to accommodate structural misfits can alter the electronic structure of Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$. The change in the electronic structure generates occupied states within the original bandgap in a favourable condition to create carriers and enlarges the density-of-states near the conduction band minimum. The present work provides insight into the various transport behaviours of thermoelectrics and topological insulators. [Preview Abstract] |
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T1.00289: The Magnon Boltzmann Transport Methods with three Magnons Scattering Tao Liu, Yuheng Li, Jianwei Zhang With rising of magnonic, the transport properties of magnon have been attracted great interests in both scientific and industry field. The magnon drag phenomenon [1,2] indicate that magnon not only can transport the coherent information with low dissipation, but also can exchange non-equilibrium magnon's current with spin current. In this work, we invent a new magnon Boltzmann equation that is derived from quantum density matrix formulas, with full magnon-magnon scattering in the scattering terms. Beside two magnons and four magnons scattering, we found that three magnons scattering act important role in magnon relaxations, since collapsing of a higher energy magnon into two lower energy magnon is described only by this three magnons process. We found that in magnetic thin film, dipole-dipole interaction, that is the causation of three magnons scattering, can be as strong as exchange interaction due to strong shape demagnetizing energy. In our theory, we found three magnons scattering engender a novel collective dynamic of magnon, which is the extending of global decay length magnon due to correlation of magnetization by short range dipole-dipole interaction. And we also study how a local magnetic field can adjust the magnon distribution by affecting diffusing length.\\ \\$[1]$Tianyu Liu, G. Vignale, Michael Flatte, Phys. Rev. Lett. 116, 237202 (2016) [2] Steven S.L. Zhang and Shufeng Zhang, Phys. Rev. Lett. 109, 096603 (2012) [Preview Abstract] |
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T1.00290: Optical response of transition-metal dichalcogenides in electric and magnetic fields Thomas Garm Pedersen, Jonas Have Semiconducting transition-metal dichalcogenides (TMDs) are characterized by unique optical properties. In their monolayer form, MoS$_2$, MoSe$_2$, WS$_2$, and WSe$_2$ are direct band gap materials with exciton binding energies reaching several hundred meVs. The excitonic optical response can be manipulated by external electric or magnetic fields. Importantly, excitons can be ionized by strong electric fields, which is crucial for efficient photocurrent generation. In this presentation, we use the Wannier exciton model to study the excitonic response in external fields [1,2]. Specifically, we compute Stark, Franz-Keldysh and Landau shifts of bound and continuum excitons. In addition, we investigate the field dependence of the exciton ionization rate. The experimental signatures of external fields are studied for a range of different TMDs in various dielectric environments. 1. T. G. Pedersen \textit{et al.}, ”Exciton ionization in multilayer transition-metal dichalcogenides”, New J. Phys. 18, 073043 (2016). 2. T. G. Pedersen, ”Exciton Stark shift and electroabsorption in monolayer transition-metal dichalcogenides”, Phys. Rev. B. 94, 125424 (2016). [Preview Abstract] |
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T1.00291: Experimental Mechanical Stochastic Resonance Jillian Rix, Barbara Breen, John Lindner Wind is free and ubiquitous and can be harnessed in multiple ways. We demonstrate stochastic resonance in a tabletop experiment that harvests wind energy to amplify weak periodic signals detected via the movement of an inverted pendulum. Unlike earlier mechanical stochastic resonance experiments, where noise was added via electrically driven vibrations, our broad-spectrum noise source is a single flapping flag. The regime of the experiment is readily accessible, with wind speeds on the order of 20 m/s and signal frequencies on the order of 1 Hz. We readily obtain signal-to-noise ratios on the order of 10 dB. [Preview Abstract] |
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T1.00292: Computational Mechanical Stochastic Resonance Yue Yu, Barbara Breen, John Lindner We computer model a table-top mechanical stochastic resonance experiment consisting of a bistable inverted pendulum, a weak periodic signal, and a flapping flag as a source of broadband noise. We identify regions of a dimensionless parameter space where applied torques create a bistable Duffing potential and allow us to independently shape the width and height of the potential barrier. The full simulation adds noise, establishes the viability of the experiment, and guides the construction of the apparatus, including the design and 3D printing of individual parts. [Preview Abstract] |
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T1.00293: Towards a Cryogen-Free MgB$_{\mathrm{2}}$-Based Superconducting Radio Frequency Accelerating Cavities Alireza Nassiri Studies on the application of Magnesium diboride (MgB$_{\mathrm{2}})$ superconducting films have shown promise for use with the radio-frequency (SRF) accelerating cavities. MgB$_{\mathrm{2\thinspace }}$coating is a potential candidate to replace bulk niobium (Nb) SRF cavities. The ultimate goal of our research is to demonstrate MgB$_{\mathrm{2}}$ coating on copper cavities to allow operation at about 20 K or so as a result of the high transition temperature (T$_{\mathrm{c}})$ of MgB$_{\mathrm{2}}$ and taking advantage of the excellent thermal conductivity of copper. Here, we will report on our recent experimental results of applying hybrid physical-chemical vapor deposition (HPCVD) to grow MgB$_{\mathrm{2}}$ films on 2-inch diameter copper discs as well as on a 2.8 GHz resonator cavity [Preview Abstract] |
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T1.00294: Modeling and simulation of microalgae derived hydrogen production in compact large scale photobioreactors Jose Vargas, Fernando Dias, Andre Mariano, Wellington Balmant, Marcos Rosa, Daiani Savi, Vanessa Kava, Chirlei Glienke, Juan Ordonez This study predicts microalgae derived hydrogen production in compact large scale photobioreactors (PBR). A transient mathematical model for the cultivation medium is developed. The tool determines the whole system temperature, and mass fractions distribution. A mathematical correlation is proposed to calculate the resulting effect on H$_{\mathrm{2}}$ production rate after genetically modifying the microalgae species. An indigenous microalgae strain was selected to be robust under different weather conditions. This strain was identified through rDNA sequence analysis, including ITS1, 5.8S and ITS2 (Internal Transcribed Spacer). The ITS analysis showed no genetic divergence between the utilized strain and \textit{Acutodesmus obliquus}. A coarse mesh was used (6048 volume elements) to obtain results for a large compact PBR (2m x 5m x 8m). The largest computational time required for obtaining results was 560 s. The numerical results for the wild species microalgal growth are validated by direct comparison to experiments. Tests were conducted in the laboratory to assess H$_{\mathrm{2}}$ production model numerical results, which are in good qualitative agreement with measurements. Therefore, the model could be used as an efficient tool for H$_{\mathrm{2}}$ production PBR systems design and control. [Preview Abstract] |
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T1.00295: Structural and superconducting features of Tl-1223 prepared at ambient pressure FNU Shipra, Athena S Sefat, Juan C Idrobo Details of bulk preparation of TlBa$_{\mathrm{2}}$Ca$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{9-\delta }}$ (Tl-1223) superconductor at ambient pressure with the critical temperature (T$_{\mathrm{c}})$ features under thermal-annealing conditions will be presented. The as-prepared Tl-1223 (T$_{\mathrm{c}}=$106K) presents a significantly higher T$_{\mathrm{c}}=$125K after annealing the polycrystalline material in either flowing Ar$+$4{\%}H$_{\mathrm{2}}$, or N$_{\mathrm{2}}$. We further refined the average bulk structures using powder XRD data. Although Ar$+$4{\%}H$_{\mathrm{2}}$ annealed Tl-1223 shows an increased 'c' lattice parameter, it shrinks by 0.03{\%} upon annealing under N$_{\mathrm{2}}$. Due to such indeterminate conclusions on the average structural changes, local structures were investigated at using aberration-corrected scanning-transmission electron microscopy technique. Similar compositional changes in the atomic arrangements of both annealed-samples of Tl-1223 were detected in which the plane containing a Ca atomic layer gives a non-uniform contrast, due to substitution of some heavier Tl. We present extensive bulk properties summarized through temperature-dependent resistivity, and shielding and Meissner fractions of magnetic susceptibility results. [Preview Abstract] |
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T1.00296: The effect of Coulomb collision on strong field QED in laser-plasma interaction. Xiaolin Jin, Yunxian Tian, Jianqing Li, Bin Li In recent years, the strong field quantum electrodynamics (QED) effects in laser-plasma interaction are paid more and more attention. Generally, the Coulomb collisions between electrons and ions and the collisions for charged particles of the same species in the plasma are considered in particle-in-cell plus Monte Carlo Collision (PIC/MCC) simulations. In this paper, the effect of the Coulomb collision on QED in laser-plasma interaction has been studied using our PIC/MCC code, BUMBLEBEE 1D, which can be used to analyze the QED effects. The binary Coulomb collision algorithm was implemented using TA model, in which a novel sorting method was applied. The evolutions of the particles in ultrahigh intensity laser (about 10$^{\mathrm{23}}$W/cm$^{\mathrm{2}})$ interaction with aluminum foil target were observed. The effects of the collision on the yields of photons and e$+$-e- pairs were discussed. The results show that there are some differences in the yields whether considering the Coulomb collision in QED-plasmas. [Preview Abstract] |
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T1.00297: Dirac magnons in collinear antiferromagnets Kangkang Li, Chenyuan Li, Yuan Li, Chen Fang We study the topological properties of magnon excitations in a large class of Heisenberg spin systems in three dimensions, where the ground state configuration is collinear and invariant under magnetic group symmetry $P*T$, a composite symmetry of time-reversal followed by space inversion. We prove that in these systems, ``Dirac points'' are symmetry-protected at band crossing between optical magnon bands, and the corresponding topological surface states have equal energy contours in the shape of non-contractible arcs, unseen in known topological materials. As a concrete example, we study a $J_1$-$J_2$ model for spin-web compound, and show the presence of the Dirac magnons using spin wave approximation. [Preview Abstract] |
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T1.00298: Interaction of Water Molecule with FE-Graphene System Gregorio Ruiz-Chavarria In this work I made a numerical simulation of the interaction between the water molecule with a Fe-graphene system. The graphene system used in this calculation is no planar, unlike the graphene widely used, but this system is a buckling system, quasi-two-dimensional system. This system has been studying previously experimental and theoretically [1]. One way to obtain graphene is from silicon carbide [2] which is subjected to thermal treatement, obtaining graphene with silicon carbide as substratum. I first obtain the stability for the graphene buckling, then add a Fe molecule, studying the stability of the system graphene buckling with Fe molecule. Finally add a water molecule, studying the evolution of the total system. I compare the obtained results with other results. To make our calculations I use Density Functional Theory, atomic pseudopotentials, Born-Openheimer approximation and Molecular Dynamic. [1] Hibino, H, et al, NTT Technical Review, Vol. 8, No 8,2010. [2] Ruan, M, et al, MRS Bulletin,Vol. 37, p. 1138 , 2012. [Preview Abstract] |
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T1.00299: Theoretical investigation of the magnetic dynamics and superconducting pairing symmetry in $\alpha$-RuCl$_3$ Wei Wang, Zhao-Yang Dong, Shun-Li Yu, Jian-Xin Li We study the spin-wave excitations in $\alpha$-RuCl$_3$ by the spin-wave theory. Starting from the five-orbital Hubbard model and the perturbation theory, we derive an effective isospin-$1/2$ model in the large Hubbard ($U$) limit. Based on the energy-band structure calculated from the first-principle method, we find that the effective model can be further reduced to the $K-\Gamma$ model containing a ferromagnetic nearest-neighbor (NN) Kitaev interaction ($K$) and a NN off-diagonal exchange interaction ($\Gamma$). With the spin-wave theory, we find that the $K-\Gamma$ model can give magnetic excitations which is consistent with the recent neutron scattering experiments. Furthermore, to investigate various particle-hole excitations and possible superconducting pairing symmetry in the doped systems, we ignore the effects of the $e_g$ orbitals and use the random-phase approximation. Our results show that the $J_{\rm eff}=1/2$ picture is robust in the doped systems, and the $d$-wave pairing is the most favourable superconducting pairing symmetry. [Preview Abstract] |
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T1.00300: A universal fluctuation diamagnetic susceptibility in cuprate superconductor Bi$_{\mathrm{\mathbf{2}}}$\textbf{Sr}$_{\mathrm{\mathbf{2-x}}}$\textbf{La}$_{\mathrm{\mathbf{x}}}$\textbf{CuO}$_{\mathrm{\mathbf{6+\delta }}}$ H. Xiao, T. Hu, Y. F. Yang, H. Q. Luo, X. M. Xie, X. J. Chen, H. K. Mao As we know, superconducting fluctuation appears at temperatures much higher than the superconducting transition temperature $T_{\mathrm{c}}$ in cuprate superconductors. It is not clear yet that how these fluctuations evolve into a superconducting condensation. In this work, we use torque magnetometer, a sensitive tool to detect magnetic signal, to study these fluctuations in Bi$_{\mathrm{2}}$Sr$_{\mathrm{2-x}}$La$_{\mathrm{x}}$CuO$_{\mathrm{6+\delta \thinspace }}$and found a universal condition under which the superconducting transition will occur, no matter the superconductor is underdoped, optimal doped or overdoped. This condition is coincident with a Bose-Einstein condensation (BEC), which reveal the nature of superconductivity in cuprate is of BEC type. The preformed cooper pairs above $T_{\mathrm{c}}$ can be viewed as bosons and follows a correlation function, which determined the strength of fluctuations. [Preview Abstract] |
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T1.00301: Electronic structures of Ce-based Kondo insulators T.-S. Nam, C.-J. Kang, D.-C. Rhyu, K. Kim, B. I. Min Topological Kondo insulators draw lots of recent attention, and so research on Kondo insulators is actively revived. SmB6 is a typical example. Among Ce-based systems, CeNiSn and CeRhSb have also been investigated as promising candidates of Kondo insulators, but it is controversial whether they are Kondo insulators or semimetals. Recent magnetothermoelectric measurement on CeNiSn suggested that CeNiSn is a nodal metal arising from anisotropic hybridization. Specific heat and thermal conductivity measurements, however, indicate that CeNiSn has an anisotropic pseudo-gap. To explore the Kondo nature in CeNiSn, we have investigated the electronic structures of CeNiSn, CeRhSb, and CeRhAs that is an isostructural material with CeNiSn, utilizing the density functional theory and the dynamical mean field theory. We have also examined the topological properties of those systems. [Preview Abstract] |
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T1.00302: Silicon Framework Allotropes for Li-ion and Na-ion Batteries: New Insight for a Reversible Capacity. Asma Marzouk, Fernando Soto, Juan Burgos, Perla Balbuena, Fadwa El-Mellouhi Silicon has the capacity to host a large amount of Li which makes it an attractive anode material despite suffering from swelling problem leading to irreversible capacity loss. The possibility of an easy extraction of Na atoms from Si24Na4 [1] inspired us to adopt the Si24 as an anode material for Lithium-ion and sodium-ion Batteries. Using DFT, we evaluate the specific capacity and the intercalation potential of Si24 allotrope. Enhanced capacities are sought by designing a new silicon allotrope [2]. We demonstrated that these Si24 allotropes show a negligible volume expansion and conserve their periodic structures after the maximum insertion/disinsertion of the ions which is crucial to prevent the capacity loss during cycling. DFT and ab-initio molecular dynamics (AIMD) studies give insights on the most probable surface adsorption and reaction sites, lithiation and sodiation, as well as initial stages of SEI formation and ionic diffusion. [1] Nat Mater 14 (2) (2015) 169 [2] Electrochimica Acta, 207 (2016) 301 [Preview Abstract] |
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T1.00303: Projective symmetry group classification of $Z_3$ parafermion spin liquids on a honeycomb lattice Zhao-Yang Dong, Shun-Li Yu, Jian-Xin Li To study the exotic excitations described by parafermions in the possible liquid states of SU(n)-spin system, we introduce a parafermion parton approach. We find that the SU(n)-spin can be decomposed into the $n$ parafermion matrices. As an application, we study the 1-dimensional(D) three-state clock model and generalized Kitaev model by a mean-field theory. Generalized Kitaev model hosts the symmetry of a combination of parity and time-reversal(PT) rather than either of them respectively. Moreover, there is also loop symmetries, which can be taken as Wilson loops in the parafermion representation. The mean-field Hamiltonian is expected to have a $Z_3$ gauge symmetry. If all the symmetries are projectively realized, its projective symmetry group(PSG) is suggested to be ($\Phi_p$)(I) due to our classification of $Z_3$ PSGs on a honeycomb lattice. We conclude that with the symmetries of translations, 6-fold rotation and PT, there are nine types and 102 solutions for 2-D $Z_3$ parafermion spin liquids on the honeycomb lattice. While, there will be nine types and 36 solutions if both parity and time-reversal symmetries are present. Our results provide a novel route for the systematic search for new types of spin liquids with parafermion excitations. [Preview Abstract] |
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T1.00304: Selectivity of adsorption of gases on doped graphene Jordan Nnabugwu, Sidi Maiga, Silvina Gatica We report our results on the selectivity of carbon dioxide being adsorbed onto doped graphene. Using the Ideal Adsorption Solution theory (IAST) we calculate the selectivity using the uptake pressures of pure gases. We focus on the adsorption of atmospheric gases such as carbon dioxide (CO$_{\mathrm{2}})$, Nitrogen (N$_{\mathrm{2}})$, and Methane (CH$_{\mathrm{4}})$ on a pure and doped monolayer graphene slab placed at the bottom of a simulation cell. Grand Canonical Monte Carlo (GCMC) simulations allow us to calculate the amount of gases adsorbed at a given temperature and pressure of the system. We found that including impurities of varying strength and concentration can increase significantly the selectivity at room temperature. [Preview Abstract] |
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T1.00305: Self-Consistent Hartree-Fock-Bogoliubov approach to the Frohlich Polaron Problem Hong Ling, Ben Kain We apply the Lee-Low-Pine (LLP) transformation to change the Frohlich model which describes a mobile impurity coupled to noninteracting phonons to an interacting many-phonon system free of impurities. We adapt the generalized Hartree-Fock-Bogoliubov (HFB) method to this impurity-free interacting many-phonon system. We specialize our general HFB description of the Frohlich polaron to Bose polarons in quasi-1D cold atom mixtures. The LLP transformed many-phonon system distinguishes itself with an artificial phonon-phonon interaction which is very different from the usual two-body interaction. We use the quasi-one-dimensional model, which is free of an ultraviolet divergence that exists in higher dimensions, to better understand how this unique interaction affects polaron states and how the density and pair correlations inherent to the HFB method conspire to create a polaron ground state with an energy in good agreement with and far closer to the prediction from Feynman's variational path integral approach than mean-field theory where HFB correlations are absent. [Preview Abstract] |
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T1.00306: Investigating heat transport within CdZnSe substrate on quality of Bolometric effect of a HgTe/HgCdTe heterostructure Mehdi Pakmehr, Mojtaba Baniasadi, Ardavan Moghtaderi, Christoph Bruene, Laurens W. Molenkamp HgTe/HgCdTe heterostructures have been investigated largely, due to its rich physics stem from spin orbit coupling (SOC), result in new class of materials (known as quantum materials) with novel properties like quantum phase transition. We probed the SOC effect combined with other mechanisms (e.g. strain, exchange many body, etc) on gapped Dirac type E($k)$ of 6.1 nm HgTe QW by a technique known as THz magneto-photoresponse spectroscopy [PRB 90, 235414, J. Ele. mat. 44, 3598]. The bolometric nature of the signals measured lead us to investigate heat diffusion mechanisms for our HgTe/HgCdTe heterostructure grown on CdZnSe [001] substrate at cryogenic temperature (1.4\textdegree K). Thermal diffusion constant ($\kappa )$ is 8 times larger for this material in comparison to other crystalline materials at low T. Modeling heat transport for our sample with Hall bar geometry confirms that CdZnSe sub. acts as a thermal heat sink when the chopped THz laser beam (40 mW @ $\nu =$1.4 THz) hits our sample (in on cycle) and as a result cools down 2DEGs confined in QW region, in microsecond scale. This allows us to modulate the temperature of 2DEGs and probe the desired physics through lock-in technique. Heat transport studies of c-CdZnSe substrate at T\textless 20\textdegree K will be presented. [Preview Abstract] |
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T1.00307: Chiral topological insulating phases from three-dimensional nodal loop semimetals Linhu Li, Chuanhao Yin, Shu Chen, Miguel Araujo We begin with a minimal model of three-dimensional nodal loop semimetals, and study the effect of anticommuting gap terms. The resulting topological insulating phases are protected by a chiral symmetry, and can be characterized by a winding number defined along the nodal loop. We illustrate the geometric relation between the nodal loop and the gap terms, which has a correspondence to the nodal loop winding number. We further investigate a lattice model and study its edge states under open boundary condition. The edge states hold Dirac cones with the same number as the summation of the winding numbers of each nodal loop in the first Brillouin zone. [Preview Abstract] |
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T1.00308: Study of quantum coherence through optical line shape of an extended excitonic system Biman Bagchi, Rajesh Dutta, Kaushik Bagchi We address the effects of quantum coherences on optical line shape of an exciton in presence of dynamic disorder. We consider a one dimensional excitonic system consisting of two levels, placed at regular intervals, coupled to a stochastic bath. An exact solution of the line shape is obtained by using Kubo's stochastic Liouville equation when bath jumps between two states obeying Poisson statistics. We utilize the fact that in site representation the system Hamiltonian with constant off-diagonal coupling J is a tridiagonal Toeplitz matrix (TDTM) with order equal to the number of sites. This is particularly useful for long chains where the exactly known eigen values help explaining the crossover between static and fast modulation limits. In the slow modulation limit effects of spatial correlation are not negligible. The line shape is also broadened and number of peak increases than that of obtained from TDTM (constant off-diagonal coupling element J and no fluctuation). However, in the fast modulation limit when the bath correlation time is small, the spatial correlation is less important. The two limits affect the line shape differently because of quantum coherence. (R Dutta and B. Bagchi, J. Chem. Phys. 145, 164907 (2016); R Dutta, K Bagchi and B Bagchi, [arXiv:1612.09409].) [Preview Abstract] |
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T1.00309: Nonlinear fluid dynamics of nanoscale hydration water layer Wonho Jhe, Bongsu Kim, QHwan Kim, Sangmin An In nature, the hydration water layer (HWL) ubiquitously exists in ambient conditions or aqueous solutions, where water molecules are tightly bound to ions or hydrophilic surfaces. It plays an important role in various mechanisms such as biological processes, abiotic materials, colloidal interaction, and friction. The HWL, for example, can be easily formed between biomaterials since most biomaterials are covered by hydrophilic molecules such as lipid bilayers, and this HWL is expected to be significant to biological and physiological functions. Here (1) we present the general stress tensor of the hydration water layer. The hydration stress tensor provided the platform form for holistic understanding of the dynamic behaviors of the confined HWL including tapping and shear dynamics which are until now individually studied. And, (2) through fast shear velocity (\textasciitilde 1mm/s) experiments, the elastic turbulence caused by elastic property of the HWL is indirectly observed. Our results may contribute to a deeper study of systems where the HWL plays an important role such as biomolecules, colloidal particles, and the MEMS. [Preview Abstract] |
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T1.00310: Lower Critical Solution Temperature (LCST) and drug conjugation of polyacetal Chathuranga De Silva, Sanjoy Samanta, Porakrit Leophairatana, Jeffrey Koberstein There has been an increasing focus in polymer research for materials that can efficiently deliver therapeutics to a pre-identified solid tumor target. Due to their unique properties, stimuli responsive polymers (SRPs) have been of particular interest. One such novel SRP is a polyacetal-based copolymer (PAC). PAC shows a remarkable temperature response (LCST) that is linearly dependent on composition. Here, we discuss the fundamental physical origins of this LCST behavior, exhibited by this polymer. Our results indicate that the observed LCST scales linearly with the number of carbon and oxygen atoms in the polymer repeat units, allowing for precise control over the LCST. We design PAC to include cancer therapeutics in its polymer-backbone, utilizing strategies to modify step-growth polymerization to obtain, for the first time, temperature-responsive main-chain drug conjugates. The temperature response in these main-chain drug conjugates allow for effective delivery of therapeutics to the tumor site, followed by acid-hydrolysis in acidic local tumor environments, to release pristine therapeutics directly at the tumor site. Due to these reasons, we foresee PAC to be in the forefront of soft-matter SRP drug-delivery systems. [Preview Abstract] |
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T1.00311: High-Efficiency Dynamic Lighting with Transition Metal Elements as Sensitizers Pragathi Darapaneni, James Dorman The lighting industry is going through several unprecedented changes over the past few years for providing energy efficient and low cost lighting. One such change is the development of Light Emitting Diodes (LEDs), which employ rare earth (RE) phosphors of Tb, Er, Eu etc. due to their unique optical and electronic properties. A major concern with the development of RE based LEDs is the availability and cost of these materials as opposed to traditional transition metal (TM) elements. However, TM based luminescence is known to be susceptible to the local crystal environment resulting in a wide range of colors based on the host materials. In this work, we propose a new class of TM based phosphors to maintain LED efficiency while simultaneously controlling luminescence based on the susceptibility of these dopants to external stimuli. For this purpose, Ni$^{\mathrm{2+}}$ doped TiO$_{\mathrm{2}}$ thin films and nanoparticles were synthesized using sol-gel chemistry and annealed for anatase and rutile crystal structures. Standard structural characterization methods were used to ensure Ni$^{\mathrm{2+}}$ dopant incorporation into the crystal lattice. The various morphologies and structures showed unique absorption spectra in the visible and NIR region, ideal for TM-RE coupling and the absorption spectra can be systematically controlled via surface functionalization with strong interfacial dipole moments. These results are modeled using time-dependent density functional theory (TD-DFT) simulations in order to design new TM-RE pairs. [Preview Abstract] |
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T1.00312: Mechanical properties of poly (butylene succinate) composites with aligned cellulose-acetate nanofibers. Tomoki Maeda, Shunta Kimura, Naruki Kurokawa, Atsushi Hotta We have developed a polymer-based nanocomposite by blending polymer nanofibers into polymer matrixes for the enhancement of the mechanical properties. In this work, we fabricated an anisotropic polymer-based nanocomposite by regulating the alignment of the nanofibers. In detail, poly (butylene succinate) (PBS), one of the most promising biodegradable polymers, was mixed with aligned cellulose acetate (CA) nanofibers made by electrospinning. CA was originally obtained as natural polymers. The aligned CA nanofibers with an average diameter of 490 nm were synthesized using a drum collector rotating at 7 m/s during the electrospinning. The PBS composites with the aligned CA nanofibers were produced by the hot-press molding, where the concentration of the CA nanofibers was 20 wt{\%}. It was found that adding aligned CA nanofibers to PBS matrix increased the Young's modulus up to 780 MPa, and that adding random CA nanofibers increased the Young's modulus up to 650 MPa. The Young's modulus of a neat PBS was 320 MPa. It was therefore confirmed that the mechanical property of PBS could be effectively improved by adding aligned nanofibers to fabricate anisotropic polymer-based nanocomposites. [Preview Abstract] |
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T1.00313: Numerical study of the ionization characteristics in ECR ion sources using PIC/MCC method. Tao Huang, Li Lei, Xiaolin Jin, Bin Li An improved computational model has been present to simulate the formation of ECR ion sources, which includes a time-dependent description of the electromagnetic fields and a self-consistent analysis of the charged particles. A method of the waveguide modal representation proposed by MAGY is used in the calculations of the electromagnetic fields. As the full solution of Maxwell's equations is reduced to one of a relatively small number of coupled partial differential equations for the amplitudes of the modes, there is a significant savings of computation time. The dynamics of the charged particle is governed by the relativistic equations of motions, and the interaction between the charged particles and microwave fields is described by particle-in-cell (PIC) method. Therefore, at each time step, a set of velocities and locations of the charged particles are calculated and used as current sources for the fields. Furthermore, the collision between charged particle and neutral particle is described by Monte Carlo Collision (MCC) method. The ionization characteristics in ECR ion sources are studied, and the effects of neutral pressure and external magnetic distribution on the ionization characteristics are also discussed. [Preview Abstract] |
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T1.00314: Synthesis and Characterization of CdS/CdS$_{\mathrm{x}}$Se$_{\mathrm{1-x}}$ Nanowires Kleyser Agueda Lopez, Marvin Wu Semiconductor nanowire heterostructures are of interest for potential applications in solar cells and other advanced optoelectronic devices. We report here on synthesis of CdS/CdS$_{\mathrm{x}}$Se$_{\mathrm{1-x}}$ nanowires (NWs) using a dual source vapor $=$ liquid -- solid technique, and characterization of these NWs with scanning electron microscopy and optical microscopy. We determine the effect of growth parameters, including source / substrate temperatures and time of exposure, on NW size, shape, and composition. The crystal structure and optical properties individual NWs from selected substrates has been mapped using transmission Kikuchi diffraction and photoluminescence (PL) microscopy. NWs consistently exhibit a hexagonal structure, with growth along the c-axis. Strong PL peaks are observed between the expected bandgap emission from CdS and CdSe, confirming formation of CdS$_{\mathrm{x}}$Se$_{\mathrm{1-x}}$. PL peaks vary significantly with intensity along the long axis of the nanowire, suggesting that the NW surface is not uniformly passivated. These nanowires show promise for future investigation and manipulation of energy band gaps contain in CdS/CdSe. [Preview Abstract] |
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T1.00315: Computational study of phonon scattering induced by dislocations Ben Xu, Yandong Sun, Yanguang zhou, Ming Hu, Yuanhua Lin Recent experiments showed dislocation-phonon interaction is important to enhance thermo-electric properties of materials. But the basic understanding of this interaction is far from satisfactory. Here, thermal conductance and phonon spectrum are carried out computationally for sample with dislocations, particularly for materials Fe and PbTe, attributed to the core and strain field of the dislocation. We find that the scattering is not limited to the traditional high frequency, but also is significant to phonon with medium frequency. Moreover, detailed analysis demonstrates how the dislocation interact with the eigen vibration mode of the material. [Preview Abstract] |
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T1.00316: Structural Stability and Electronic Properties of Two Dimensional Transition Metal Carbides Jinying Wang, Atsushi Oshiyama Numerous two dimensional (2D) materials have been developed since the discovery of graphene. High-quality 2D ultrathin Mo2C films have been successfully fabricated recently [1], but little research on their properties is reported. In this study, we have investigated the structural stability and electronic properties of 2D transition metal carbides (TMC) using first-principles calculations. The pressure of hydrogen are found to be very important for the thickness and surface structure of TMC. The electronic properties of TMC are indicated to strongly dependent on number of d electrons. Nearly all systems are metallic except one. Meanwhile, strain-induced transition between metallic and semi-metallic states have also been found. [1] Xu, C.; Wang, L.; Liu, Z.; Chen, L.; Guo, J.; Kang, N.; Ma, X.-L.; Cheng, H.-M.; Ren, W., Large-area high-quality 2D ultrathin Mo2C superconducting crystals. Nat Mater 2015, 14 (11), 1135-1141. [Preview Abstract] |
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T1.00317: Strong coupling optical spectra in dipole-dipole interacting Tavis-Cummings models Imran Mirza Hybrid quantum systems offer novel and unique platforms for quantum technologies [G. Kurizki et.al, PNAS, 112 (13), 3866-3873 (2015)]. Hybrid atom-optomechanics (HAOM) is fascinating example in this context. In these Hybrid systems, a wealth of phenomena can arise due to the presence of coherent atom-light and light-mechanics interactions at the quantum level. From the perspective of practical utilizations of these HAOM systems in future quantum devices, the understanding of the excitation dynamics as well as spectral features is crucial. In this poster, I'll present single-photon emission spectrum of an optomechanical cavity strongly coupled to two dipole-dipole interacting qubits (Optomechanical Tavis-Cummings model) [I. M. Mirza, Opt. Lett., 41, 11, (2016)]. Particularly, I'll discuss the influence of dipole-dipole interaction on the single photon spectrum under a strong qubit-cavity interaction. I'll also exhibit the amenability of model to the inclusion of mechanical losses and spontaneous emissions under a non-local Lindblad model. [Preview Abstract] |
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T1.00318: Rapid and ultrasensitive flexible palladium nano-thin film biosensing electrode development for cancer antigen HER2 detection Yun-Tzu Huang, Chia-Yu Chang, Wei Chen, Chien-Hao Su, Guo-Cheng Hsu, Chia-Ching Chang HER2 (human epidermal growth factor receptor 2) is one of the significant surface antigens of breast cancer Trace amount of HER2 protein in human serum is highly correlated to the tumor progression in breast cancers especially in the cases of recurrence. Therefore, HER2 detection of human serum is significant for early detection of cancer recurrence. Conventional HER2 detection approaches may not be sensitive enough or contain highly false positive rate or time consuming for accurate detection. Therefore, a rapid, highly sensitive and specific sensing is highly desired. By using HER2 specific binding peptide functionalized palladium thin film electrochemical electrode the HER2 protein concentration can be determined at sub-nanogram level by electrochemical impedance spectroscopy (EIS) within 10 mins. The Pd nano-film is sputtered on the flexible plastics substrate and reduces the cost of this electrode. Due to the low cost of the electrode, it is designed as a disposable biosensing probe which may reduce the concern of human sample contamination. The self-management after breast cancer operation may be feasible in the near future.\\ \\Keywords: Electrochemical impedance spectroscopy(EIS), breast cancer, biosensor [Preview Abstract] |
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T1.00319: First-principles calculations that clarify energetics and reactions of oxygen adsorption and carbon desorption on 4H-SiC (11-20) surface Han Li, Yu-ichiro Matsushita, Mauro Boero, Atsushi Oshiyama Silicon carbide(SiC) is a well-known and now an emerging semiconductor material for power electronics due to its wide band-gap and the robustness under harsh environment. Oxidation of SiC leads to the formation of SiO$_{\mathrm{2}}$ on the semiconductor surface which is essential in the transistor action of the devices, as in the case of Si. However, the formation of the SiO$_{\mathrm{2\thinspace }}$films on the compound semiconductor SiC is much more complicated phenomenon since oxygen reacts with both Si and C, and then C atoms are eventually annihilated. We report static and dynamical first-principles calculation that provide atomistic pictures at the initial stage of the oxidation of the (11-20) surface of 4H-SiC. The oxygen adsorption shows structural multi-stability and the surface bridge sites are the most stable. An arriving O$_{\mathrm{2}}$ molecule is adsorbed, dissociated and then migrates toward these surface bridge sites with the free-energy barrier of 0.7 eV. We also find that a CO molecule is desorbed from the metastable oxidized structure with the free-energy barrier of about 2.5 eV. Drastic reduction of the CO desorption energy is found on the (000-1) surface and the reason is clarified to be the electron transfer from the Si to C dangling bonds. [Preview Abstract] |
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T1.00320: Study of the Aharonov-Bohm effect: a derivation of one particle quantum mechanics from quantum field theory Benliang Li, Daniel Hewak, Qijie Wang In this article, we start with the discussions on the Aharonov-Bohm effect then raise a plausible interpretation within the quantum electrodynamics (QED) framework. We provide a quantum treatment of the source of the electromagnetic potential and argue that the underlying mechanism in AB effect can be viewed as interactions between electrons described by QED theory where the interactions are mediated by virtual photons. On further analysis, we show that the framework of one particle quantum mechanics (OPQM) can be given, in general, as a mathematically approximated model which is reformulated from QED theory while the Aharonov-Bohm effect scheme provides a platform for our derivations. In addition, the classical Maxwell equations are derived from QED scattering process while both classical electromagnetic fields and potentials serve as mathematical tools that are constructed to approximate the interactions among elementary particles described by QED physics, i.e., neither classical fields nor potentials represent any real entities of nature. [Preview Abstract] |
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T1.00321: Exact Calculation of the Thermodynamics of Biomacromolecules on Cubic Recursive Lattice. Ran Huang The thermodynamics of biomacromolecules featured as foldable polymer with inner-linkage of hydrogen bonds, e. g. protein, RNA and DNA, play an impressive role in either physical, biological, and polymer sciences. By treating the foldable chains to be the two-tolerate self-avoiding trails (2T polymer), abstract lattice modeling of these complex polymer systems to approach their thermodynamics and subsequent bio-functional properties have been developed for decades. Among these works, the calculations modeled on Bethe and Husimi lattice have shown the excellence of being exactly solvable. Our project extended this effort into the 3D situation, i.e. the cubic recursive lattice. The preliminary exploration basically confirmed others' previous findings on the planar structure, that we have three phases in the grand-canonical phase diagram, with a 1st order transition between non-polymerized and polymer phases, and a 2nd order transition between two distinguishable polymer phases. However the hydrogen bond energy J, stacking energy $\varepsilon $, and chain rigidity energy H play more vigorous effects on the thermal behaviors, and this is hypothesized to be due to the larger number of possible configurations provided by the complicated 3D model. By the so far progress, the calculation of biomacromolecules may be applied onto more complex recursive lattices, such as the inhomogeneous lattice to describe the cross-dimensional situations, and beside the thermal properties of the 2T polymers, we may infer some interesting insights of the mysterious folding problem itself. [Preview Abstract] |
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T1.00322: Formation of Graphene field Effect Devices with Periodic Uniaxial Strain and Its Semiconducting Electron Transport Hikari Tomori, Rineka Hiraide, Youiti Ootuka, Akinobu Kanda Strain engineering is a promising but unexplored method of inducing band gaps in graphene. So far, a band gap in graphene induced by periodic uniaxial strain has been observed in scanning tunnel spectroscopy studies, while it has not been confirmed in actual field effect devices. This missing gap is presumably due to the relaxation of strain in device fabrication processes. Here, we develop a novel device fabrication method which makes graphene largely strained even after the formation of electrical contacts. The back gate voltage dependence of the conductance in the strained graphene exhibits remarkable difference from the conventional V-shaped curve observed in graphene placed on SiO2. The minimum conductivity shows thermal activation behavior at high temperatures. From the Arrhenius plot, the band gap is estimated to be 2.4 meV. Besides, the current-voltage characteristics become nonlinear around the origin. The high resistance region extends in a region of $+$/- 2 meV around the charge neutrality point, which agrees with the band gap estimated from the temperature dependence. These observations confirm the formation of the band gap in our strained graphene. We expect that optimization of the device structure extends the gap and improves device performance. [Preview Abstract] |
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T1.00323: Towards a new two-dimensional ZnO monolayer from cluster Assembly Anjali Kshirsagar, Prashant Gaikwad, Sudip Chakraborty, Pradeep Pujari Two-dimensional structures, particularly of II-VI semiconductors, are being studied due to their technological applications stemming from their unique electronic properties. ZnO has been studied both experimentally and theoretically in bulk as well as in various nanostructured forms due to its wide band gap and large exciton energy. Monolayer ZnO has been recently synthesized experimentally and has been studied theoretically in hexagonal form. We propose a new octagonal ZnO monolayer, formed computationally by assembling stable geometries of passivated (ZnO)$_{\mathrm{2\thinspace }}$and (ZnO)$_{\mathrm{4}}$ clusters. The stability of the monolayer has been established via the total energy, formation energy, phonon dispersion and thermal properties. Detailed electronic structure calculations and analysis on the basis of site projected local density of states, partial charge density and Bader charge analysis bring out the changes in hybridization in comparison to the known hexagonal monolayer. These are attributed to difference in the coordination and bonding among the Zn and O atoms. Possible applications for gas sensing and water splitting will be discussed. [Preview Abstract] |
(Author Not Attending)
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T1.00324: Nonlinear Spectral Singularity and Laser Output Intensity for the TE and TM Modes Hamed Ghaemidizicheh, Ali Mostafazadeh The nonlinear spectral singularity arising from a Kerr nonlinearity is explored in [Phys. Rev. A 87, 063838 (2013)]. This reference studies the effect of nonlinearity in Lasing condition and shows that Kerr nonlinearity with spectral singularity for a normally incident wave provides an explanation of lasing at gain coefficient $g$. Lasing occurs when it exceeds threshold gain $g_{0}$. For oblique waves, Ref. [Phys. Rev. A 91, 043804 (2015)] looks at the behavior of threshold gain coefficient $g_{0}$ which is given by the condition that there is a linear spectral singularity. We investigated imposing the condition of the existence of nonlinear spectral singularity in the $TE/TM$ modes of a mirrorless slab of gain materials and studied the $\theta$-dependence of intensity. [Preview Abstract] |
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T1.00325: Realization of Massive Relativistic Spin-$3/2$ Rarita-Schwinger Quasiparticle in Condensed Matter Systems Feng Tang, Xi Luo, Yongping Du, Yue Yu, Xiangang Wan Very recently, there has been significant progress in realizing high-energy particles in condensed matter system (CMS) such as the Dirac, Weyl and Majorana fermions. Besides the spin-1/2 particles, the spin-3/2 elementary particle, known as the Rarita-Schwinger (RS) fermion, has not been observed or simulated in the laboratory. The main obstacle of realizing RS fermion in CMS lies in the nontrivial constraints that eliminate the redundant degrees of freedom in its representation of the Poincar\'{e} group. In this Letter, we propose a generic method that automatically contains the constraints in the Hamiltonian and prove the RS modes always exist and can be separated from the other non-RS bands. Through symmetry considerations, we show that the two dimensional (2D) massive RS (M-RS) quasiparticle can emerge in several trigonal and hexagonal lattices. Based on \emph{ab initio} calculations, we predict that the thin film of CaLiX (X=Ge and Si) may host 2D M-RS excitations near the Fermi level. [Preview Abstract] |
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T1.00326: TBD Lemi Deja, Mulugeta Bekele The research work that I intend to present mainly deals with the the transport properties of charge carriers in $\pi $-conjugated polymeric materials using a Monte Carlo simulation technique. The transport model is based on uncorrelated on-site disorder energy which is extracted from a Gaussian distribution function of material specific width. The basic transport process is described by the Miller-Abrahams type of hopping rate and a Monte Carlo approach is used to calculate the charge carrier distribution in the conducing channel as well as the mobilities of the carriers as a function of source-drain electric field, temperature and charge carrier concentration. The Coulomb interaction potential between charge carriers has been incorporated, and the mobility of a conjugated polymer used as electroactive material in a field-effect transistor device has been calculated. [Preview Abstract] |
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T1.00327: Effect of surface plasmonic resonance on energy transfer in inorganic/organic hybrid thin film Nobuko Arai, Ryoko Shimada Forster Resonance Energy Transfer (FRET) occurs between a donor and an accepter. In addition, a metal (for example, silver) could enhance this energy transfer due to the surface plasmon effect. This study focuses on hybrid, thin films consisting of layers of zinc oxide (ZnO), silver (Ag), and a polymeric matrix (polymethyl methacrylate) containing anthracene stacked in this order. The ZnO/Ag/anthracene-PMMA hybrid showed the PL intensity larger than that from the ZnO/anthracene-PMMA, possibly due to the surface plasmon effect in the former. Moreover, the blue-shifts was observed for the emission peaks in the Ag plasmonic absorption energy. Detailed results will be presented on site. [Preview Abstract] |
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T1.00328: Tunneling transport of mono- and few-layers magnetic van der Waals MnPS$_{\mathrm{3}}$ Sungmin Lee, Ki-Young Choi, Sangik Lee, Bae Ho Park, Je-Geun Park We have investigated the tunneling transport of mono- and few-layers of MnPS$_{\mathrm{3}}$ by using conductive atomic force microscopy. Due to the band alignment of indium tin oxide/MnPS$_{\mathrm{3}}$/Pt-Ir tip junction, the key features of both Schottky junction and Fowler-Nordheim tunneling (FNT) were observed for all the samples with varying thickness. Using the FNT model and assuming the effective electron mass (0.5 $m_{e})$ of MnPS$_{\mathrm{3}}$, we estimate the tunneling barrier height to be 1.31 eV and the dielectric breakdown strength as 5.41 MV/cm. [Preview Abstract] |
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T1.00329: Spectra, current flow and wave function morphology in a model PT-symmetric quantum dot with external interactions Felix Tellander, Karl-Fredrik Berggren We use numerical simulations to study a two-dimensional (2D) quantum dot (cavity) with two leads for passing currents (electrons, photons, etc.) through the system. By introducing an imaginary potential in each lead the system is made symmetric under parity-time inversion ($\mathcal{PT}-$symmetric). This system is experimentally realizable in the form of e.g. quantum dots in low-dimensional semiconductors, optical and electromagnetic cavities and other classical wave analogues. The computational model introduced here for studying spectra, exceptional points (EPs), wave function symmetries and morphology, and current flow includes thousand of interacting states. This supplements previous analytic studies of few interacting states by providing more detail and higher resolution. The Hamiltonian describing the system is non-Hermitian, thus the eigenvalues are in general complex. The structure of the wave functions and probability current densities are studied in detail at and in between EPs. The statistics for EPs is evaluated and reasons for a gradual dynamical crossover (DC) are identified. [Preview Abstract] |
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T1.00330: Measuring mouse retina response near the detection threshold to direct stimulation of photons with sub-poisson statistics Amir Tavala, Krishna Dovzhik, Klaus Schicker, Alexandra Koschak, Anton Zeilinger Probing the visual system of human and animals at very low photon rate regime has recently attracted the quantum optics community. In an experiment on the isolated photoreceptor cells of Xenopus, the cell output signal was measured while stimulating it by pulses with sub-poisson distributed photons. The results showed single photon detection efficiency of 29$+$/-4.7{\%} [1]. Another behavioral experiment on human suggests a less detection capability at perception level with the chance of 0.516$+$/-0.01 (i.e. slightly better than random guess) [2]. Although the species are different, both biological models and experimental observations with classical light stimuli expect that a fraction of single photon responses is filtered somewhere within the retina network and/or during the neural processes in the brain. In this ongoing experiment, we look for a quantitative answer to this question by measuring the output signals of the last neural layer of WT mouse retina using microelectrode arrays. We use a heralded downconversion single-photon source. We stimulate the retina directly since the eye lens (responsible for 20-50{\%} of optical loss and scattering [2]) is being removed. Here, we demonstrate our first results that confirms the response to the sub-poisson distributied pulses. [Preview Abstract] |
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T1.00331: Super-Tough Hybridgels Comprising of Mesoporous Silica Microrods and Double-Network Polymers for On-Demand Drug Delivery by Mechanical Stimulation Suji Choi, Youngjin Choi, Jaeyun Kim Although hydrogels are useful for various industrial and biomedical applications such as drug/cell delivery, tissue engineering, and regenerative medicine, they have been often suffered from their weak mechanical properties. Over the past decades, a lot of strategies have been studied for overcoming the disadvantages of the conventional hydrogels. Here, we suggest a super-tough composite hybrid hydrogels (hybridgels) comprising of alginate/polyacrylamide double-network hydrogels embedded with mesoporous silica mocrorods (SBA-15). The super-toughness was attained from an efficient energy dissipation by multiple bondings between polymers and SBA-15. The superior mechanical properties of these hybridgels make it possible to maintain their structure for a long period of time in a physiological solution. Based on high mechanical stability, the hybridgels were demonstrated to exhibit on-demand drug release, which was controlled by an external mechanical stimulation. Moreover, different types of drugs can be separately loaded into the hydrogel network and mesopores of SBA-15 and can be released with different speeds, suggesting that these hydrogels could be used for multiple drug release. [Preview Abstract] |
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T1.00332: Detection and Analysis of the Magnetic Field Component of Electromagnetic Radiation Emission from Macroscopic Fracturing of Cement-Bound Granular Material Paul Ivan Ceralde, Joel Tiu Maquiling This study aims to detect and measure the magnetic field component of the Electromagnetic Radiation (EMR) emitted by quasi-brittle materials that undergo macroscopic fracturing. Cement-Bound Granular Materials (CBGM) were prepared by mixing cement, sand and gravel in a beam mold. Additional aggregates in the form of saw dust were added to produce variable CBGM samples. A concrete beam holder was designed and fabricated such that induced cracks from impact loading would form at the center of the beam. Six Vernier software magnetic field sensors were used to detect the magnetic field (MF) component of the EMR emission. The magnetic field sensors were set at a low amplification range (\textpm 6.4x10$^{\mathrm{-3}}$ T) setting with 0.0002 mT precision at 20-50 Hz. Sensor locations and orientations were specified and fixed throughout the experiment. The impact loading process was repeated until concrete failure. The time of drop was determined through the occurrence of peak sound levels (dB) induced by the collision noise using a sound level meter at fast time weighting. Magnetic field fluctuations manifesting near the occurrence of sound level impulses were recorded. Peak magnetic field values within \textpm 200ms from the recorded time of impact were considered to be originating from the concrete fracture. [Preview Abstract] |
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T1.00333: Analysis of the Angle of Maximal Stability and Flow Regime Transitions in Different Proportions of Bi-phasic Granular Matter Mixtures Joel Tiu Maquiling, Shane Marie Visaga This study investigates the dependence of the critical angle $\theta $c of stability on different mass ratios $\gamma $ of layered bi-phasic granular matter mixtures and on the critical angle of its mono-disperse individual components. It also aims to investigate and explain regime transitions of granular matter flowing down a tilted rough inclined plane. Critical angles and flow regimes for a bi-phasic mixture of sago spheres and bi-phasic pepper mixture of fine powder and rough spheres were observed and measured using video analysis. The critical angles $\theta_{\mathrm{c\thinspace MD}}$ of mono-disperse granular matter and $\theta_{\mathrm{c\thinspace BP}}$ of biphasic granular matter mixtures were observed and compared. All types of flow regimes and a supramaximal critical angle of stability exist at mass ratio $\gamma \quad =$ 0.5 for all biphasic granular matter mixtures. The $\theta_{\mathrm{c\thinspace BP\thinspace }}$of sago spheres was higher than the $\theta_{\mathrm{c\thinspace MD}}$ of sago spheres. Moreover, the $\theta_{\mathrm{c\thinspace BP}}$ of the pepper mixture was in between the $\theta_{\mathrm{c\thinspace MD}}$ of fine pepper and $\theta_{\mathrm{c\thinspace MD}}$ of rough pepper spheres. Comparison of different granular material shows that $\theta_{\mathrm{c\thinspace MD}}$ is not simply a function of particle diameter but of particle roughness as well. Results point to a superposition mechanism of the critical angles of biphasic sphere mixtures. [Preview Abstract] |
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T1.00334: Atomic structures of B20 FeGe thin films grown on the Si(111) surface Wondong Kim, Seungkyun Noh, Jisoo Yoon, Young Heon Kim, Inho Lee, Jae-Sung Kim, Chanyong Hwang We investigated the growth and atomic structures of FeGe thin films on the Si (111) surface by using scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). The 2 \textasciitilde 5nm- thick FeGe thin films were prepared on the clean Si(111) 7x7 surface by co-deposition of Fe and Ge from separated electron-beam evaporators. With direct deposition on the substrate at the temperature above 550 K, the surface of FeGe films was not smooth and consisted of coarse grains. By the combination of room-temperature annealing and post-annealing process around 800 K, the structure of FeGe thin films evolved into the well crystalized structures. Atom-resolved STM images revealed that there are at least four different surface terminations. We constructed atomic models for each surface terminations based on the bulk atomic arrangement of a B20 chiral structure and confirmed that the observed STM images are successfully reproduced by using computational simulations employing Vienna Ab Initio Simulation package (VASP) with a B20 chiral structure model. TEM cross-sectional images also support our atomic models by revealing clearly the characteristic zigzag features of B20 structures of FeGe(111) thin films. [Preview Abstract] |
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T1.00335: Overview of graduate training program of John Adams Institute for Accelerator Science Andrei Seryi The John Adams Institute for Accelerator Science is a center of excellence in the UK for advanced and novel accelerator technology, providing expertise, research, development and training in accelerator techniques, and promoting advanced accelerator applications in science and society. We work in JAI on design of novel light sources – upgrades of 3-rd generation and novel FELs, on plasma acceleration and its application to industrial and medical fields, on novel energy recovery compact linacs and advanced beam diagnostics, and many other projects. The JAI is based on three universities – University of Oxford, Imperial College London and Royal Holloway University of London. Every year 6 to 10 accelerators science experts, trained via research on cutting edge projects, defend their PhD thesis in JAI partner universities. In this presentation we will overview the research and in particular the highly successful graduate training program in JAI. [Preview Abstract] |
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T1.00336: Growth and properties of semi-metallic and semiconducting phases of MoTe$_{\mathrm{2}}$ monolayer by molecular-beam epitaxy Jinglei Chen, Guanyong Wang, Yanan Tang, Jinpeng Xu, Xianqi Dai, Jinfeng Jia, Wingkin Ho, Maohai Xie Hexagonal (2H) and distorted octahedral (1T') phases are the~two common structures of~monolayer MoTe$_{\mathrm{2}}$~showing, respectively, semiconducting and semi-metallic properties. The formation energies between the two structures of~MoTe$_{\mathrm{2}}$~are almost equal, so there is a high chance to tune the structures of MoTe$_{\mathrm{2}}$~and to bring in new applications such as phase-change electronics. In this work, we report growth of both 2H and 1T' MoTe$_{\mathrm{2}}$~ML by molecular-beam epitaxy (MBE) and demonstrate the tunability of the structural phases~by changing the growth conditions of MBE. We present experimental and theoretical evidences showing the important role of Te surface adsorption in promoting and stabilizing the otherwise metastable 1T'-MoTe$_{\mathrm{2}}$~during MBE.~By scanning tunneling microscopy and spectroscopy,~we also reveal~quantum dot states and quantum inter-valley~interference~patterns~in the 2H and 1T' domains, respectively. [Preview Abstract] |
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T1.00337: Ultra-tough and strong, hybrid thin films based on ionically crosslinked polymers and 2D inorganic platelets Dong Hwan Ji, Suji Choi, Jaeyun Kim Integration of high strength and toughness tend to be mutually exclusive and synthesized hybrid films with superior mechanical properties have been difficult to fabricate controllable shapes and various scales. Although diverse synthesized hybrid films consisting of organic matrix and inorganic materials with brick-and-mortar structure, show improved mechanical properties, these films are still limited in toughness and fabrication methods. Herein, we report ultra-tough and strong hybrid thin films with self-assembled uniform microstructures with controllable shapes and various scale based on hydrogel-mediated process. Ca$^{\mathrm{2+}}$-crosslinking in alginate chains and well-aligned alumina platelets in alginate matrix lead to a synergistic enhancement of strength and toughness in the resulting film. Consequentially, Ca$^{\mathrm{2+}}$-crosslinked Alg/Alu films showed outstanding toughness of 29 MJ m$^{\mathrm{-3}}$ and tensile strength of 160 MPa. Furthermore, modifying Alu surface with polyvinylpyrrolidone (PVP), tensile strength was further improved up to 200 MPa. Our results suggest an alternative approach to design and processing of self-assembled hydrogel-mediated hybrid films with outstanding mechanical properties. [Preview Abstract] |
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T1.00338: Thickness-dependent native strain in graphene membranes visualized by Raman spectroscopy Sunmin Ryu, Sujin Kim Since graphene has an extreme surface-to-volume ratio, its various material properties are known to be susceptible to interactions with environment. Its high stretchability, in particular, allows graphene to conform well to external perturbation, which leads to modifications of its electronic, magnetic and chemical properties. In this work, we report a Raman spectroscopic strain metrology and visualize the native strain induced by the van der Waals interactions of mechanically exfoliated graphene of varying thickness with supporting silica substrates. Using freestanding graphene as a strain-free and charge-neutral reference, we quantified the resulting strain with a resolution of 0.02{\%} and found that its spread decreases as increasing the number of layers finally reaching the detection limit for the thickness of \textasciitilde 30 layers. The spatially resolved strain maps revealed that the native strain is randomly distributed and that both of compression and expansion are also randomly generated. The current optical analysis can serve as a highly sensitive and efficient strain metrology tool for graphene samples in a wide range of thickness and can be extended to other 2-dimensional crystal systems. [Preview Abstract] |
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T1.00339: Quantum Mechanical Calculations of Free Energy and Open-Circuit Voltage in Lattice Modeled Organic Photovoltaic Devices. Vladimir Lankevich, Eric Bittner In organic photovoltaic devices (OPVs), initially bound electron and hole can take many different paths to dissociate and become free charge carriers. This leads to the increase in their density of states and therefore increase in the entropy of the system.\footnote{T. M. Clarke, J. R. Durrant, \textbf{Chem. Rev.}, 110, 11} Accurate description of the energy barriers that charges have to overcome, therefore requires calculation of the free energy.\footnote{S. N. Hood, I. Kassal, \textbf{JPC Letters}, 7, 22} Free energy of an OPV is directly related to its open-circuit voltage and depends only on few important parameters such as average life-time of a charge-transfer state, average energy of the charge-transfer state and energetic disorder in the system.\footnote{T. M. Burke, S. Sweetnam, K. Vandewal, M. D. McGehee, \textbf{Adv. Energy Mat.},5,11} We extend these ideas to the quantum mechanical simulations of the dissociation in the lattice modeled bulk-heterojunction system. We observe average excitonic and free energies that agree with theoretical predictions and the number of experimental results from previous studies. We study effects of the energy disorder and importance of the dimensionality and morphology in materials such as polymer-fullerene blends. [Preview Abstract] |
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T1.00340: Effect of Slope and Packing Ratio on the Behavior of Matchsticks Burnings Priya Karna, Sunil Karna The experiment was conducted to demonstrate the behavior of fire propagation on wildland using matchsticks forest model. A model forest was designed on a flame resistance clay, on top of which matchsticks were inserted and kept vertical to the ground by keeping spacing between them constant with the help of aluminum grid. The data for distance traveled by fire with time was taken at wide range of slopes from downhill of $-25^{o}$ to uphill of $45^{o}$ on model forests of packing ratios of 0.08 and 0.04. The minimum rate of fire spread was observed around $15^{o}$ downhill. The data collected from this experiment follows nature of $tan^{2}\theta$ and agrees with Rothermel mathematical model of fire propagation except at high elevation above $35^{o}$ for low packing ratio. [Preview Abstract] |
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T1.00341: Universal Dynamics of a localized excitation after an interaction quench Fabio Franchini We study the time evolution -induced by a quench- of local excitations in one dimension. We focus on interaction quenches: the considered protocol consists in creating a stable localized excitation propagating through the system, and then operating a sudden change of the interaction between the particles. To highlight the effect of the quench, we take the initial excitation to be a soliton. The quench splits the excitation into two packets moving in opposite directions, whose characteristics can be expressed in a universal way. Our treatment, which is hydrodynamic in nature, allows to describe the internal dynamics of these two packets in terms of the different velocities of their components. We confirm our analytical predictions through numerical simulations performed with the Gross-Pitaevskii equation and with the Calogero model (as an example of long range interactions and solvable with a parabolic confinement). Through the Calogero model we also discuss the effect of an external trapping on the protocol. The hydrodynamic approach shows that there is a difference between the bulk velocities of the propagating packets and the velocities of their peaks, accessible through different measurement procedures. -J. Phys. A: Math. Theor. 48 (2015) 28FT01; -New J. Phys. 18 (2016) 115003 [Preview Abstract] |
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T1.00342: Flow-stabilized levitation in a magnetic stirrer. Kyle Baldwin, David Fairhurst, Jean-Baptiste de Fouchier, Patrick Atkinson, Thomas Darwent, Richard Hill, Michael Swift Magnetic stirrers are a useful tool for preparing solutions as the mixing vessel can be completely sealed, with no physical contact between the drive magnet and stir-bar. However, colloquially, stir-bars are known as ``fleas'' due to the onset of jumping at high speeds, which halts mixing. Here, we investigate the transition from spinning to jumping and discover an intriguing additional state, where the flea is levitated several centimeters while moving in a superposition of rotation and oscillation. This is of interest as Earnshaw's theorem states that there is no arrangement of static permanent magnets that be levitated stably. Current mag-lev technology side-steps this via secondary effects ($e.g.$ diamagnetic repulsion or superconductive flux-line pinning), none of which can account for the flea's stability. We map the equations of motion onto a driven damped-pendulum system, universally characterize the onset of jumping, and successfully predict the oscillating flea's behavior. We further find that the stability is maintained by the flea's oscillation, which, at intermediate Reynolds numbers (Re $\approx $ 10), pumps fluid out from the ends of the flea, creating a streaming flow that centers it. If, however, Re is too low/too high, the respective flows are reciprocal/reversed, which both destabilize the levitation. This levitation technique demonstrates increasing Re can reverse the streaming flows relevant to propulsion, and could be cheaply implemented to study a variety of fluid and biological systems. [Preview Abstract] |
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T1.00343: Substrate dependent proximity effect of niobium film Danho Ahn, Won-Jun Jang, Chanyoung Lim, Dojun Yum, Jhinhwan Lee, Yannis Semertzdis Proximity effect between superconductor (SC) and normal metal (NM) is manifested as the diminished superconductivity in SC film by NM substrate. We have studied the magnetron-sputtered and post-annealed niobium film on two different substrates, stainless steel 316 and OFHC copper ($\rho _{\mathrm{SUS}}$/$\rho_{\mathrm{Cu}}\sim $10$^{\mathrm{2}})$. The research shows that a larger conductivity in NM substrate results in a more strongly suppressed superconductivity of the deposited film. We will also show comparison of other characteristics of the SC films related to the superconductivity with analysis techniques such as AFM (atomic force microscopy), SEM (scanning electron microscopy), XPS (x-ray photoelectron spectroscopy), PPMS (physical property measurement system) and MPMS (magnetic property measurement system). [Preview Abstract] |
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T1.00344: Molecular dynamics simulations of H$_{\mathrm{2}}$O, NO$_{\mathrm{2}}$, and N$_{\mathrm{2\thinspace }}$mixtures on graphene. Hawazin Alghamdi, Silvina Gatica In this work we study the adsorption of mixtures of H$_{\mathrm{2}}$O, NO$_{\mathrm{2}}$, and N$_{\mathrm{2}}$ on graphene using the method of Molecular Dynamics. We run the simulations at constant temperatures from 100K to 230K. The H$_{\mathrm{2}}$O and NO$_{\mathrm{2}}$ molecules are modeled as a rigid 3-point systems and N$_{\mathrm{2}}$ is considered a spherical super-atom with Lenard-Jones interactions. The substrate is a rigid graphene layer located at the bottom of the simulation cell. The LJ parameters of interaction between the molecules and the graphene are calculated by fitting the atomistic pair-wise sum of carbon-atom interactions with the 9-3 potential. We calculate the selectivity of NO$_{\mathrm{2}}$/N$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O/N$_{\mathrm{2\thinspace }}$on graphene to test the capability of graphene to separate nitrogen dioxide or water from air. [Preview Abstract] |
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T1.00345: Molecular dynamics study of dual-phase microstructure of Titanium and Zirconium metals during the quenching process Narumasa Miyazaki, Kazunori Sato, Yoji Shibutani Dual-phase (DP) transformation, which is composed of felite- and/or martensite- multicomponent microstructural phases, is one of the most effective tools to product functional alloys. To obtain this DP structure such as DP steels and other materials, we usually apply thermal processes such as quenching, tempering and annealing. As the transformation dynamics of DP microstructure depends on conditions of temperature, annealing time, and quenching rate, physical properties of materials are able to be tuned by controlling microstructure type, size, their interfaces and so on. In this study, to understand the behavior of DP transformation and to control physical properties of materials by tuning DP microstructures, we analyze the atomistic dynamics of DP transformation during the quenching process and the detail of DP microstructures by using the molecular dynamics simulations. As target metals of DP transformation, we focus on group 4 transition metals, such as Ti and Zr described by EAM interatomic potentials. For Ti and Zr models we perform molecular dynamics simulations by assuming melt-quenching process from 3000 K to 0 K under the isothermal--isobaric ensemble. During the process for each material, we observe liquid to HCP like transition around the melting temperature, and continuously HCP-BCC like transition around martensitic transformation temperature. Furthermore, we clearly distinguish DP microstructure for each quenched model. [Preview Abstract] |
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T1.00346: An Alternative Representation of Mechanical Metamaterials for Visualizing the Unfolding Process K.C. Chan Ahmad Rafsanjani and Damiano Pasini recently exhibited some design variations of planar mechanical metamaterial inspired by Islamic Motifs.* It is a challenge to visualize the expansion of the motifs, modulated and connected by hinges, ahead of time from its original state. A close scrutiny of these new designs reveals that they can be equivalently described in the language of space expansion, of a Bravis unit cell, conservation of mass, conservation of total angular momentum to predict the expansion without having to track complicated movements of the interconnected hinges. Such a consideration greatly simplifies mathematics involved and could provide insights to new designs. *APS news, A Medley of Metamaterials, April 2016 (Volume 25, Number 4, Page 3) www. aps. org/ publications/ apsnews/ 201604/metamaterials .cfm. [Preview Abstract] |
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T1.00347: Graphene quantum dot synthesis using nanosecond laser pulses and its comparison to Methylene Blue Khomidkhodza Kholikov, Zachary Thomas, Dovletgeldi Seyitliyev, Skylar Smith A biocompatible photodynamic therapy agent that generates a high amount of singlet oxygen with high water dispersibility and excellent photostability is desirable. In this work, a graphene based biomaterial which is a promising alternative to a standard photosensitizers was produced. Methylene blue was used as a reference photosensitizer. Bacteria deactivation by methylene blue was shown to be inhibited inside human blood due to protein binding. Graphene quantum dots (GQD) were synthesized by irradiating benzene and nickel oxide mixture using nanosecond laser pulses. High resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) were used for characterization of GQDs. Initial results show graphene quantum dots whose size less than 5 nm were successfully obtained. UV-VIS spectra shows absorption peak around 310 nm. The results of these studies can potentially be used to develop therapies for the eradication of pathogens in open wounds, burns, or skin cancers. New therapies for these conditions are particularly needed when antibiotic-resistant infections are present. [Preview Abstract] |
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T1.00348: Approaching Terahertz Range with 3-color Broadband Coherent Raman Micro Spectroscopy Laszlo Ujj, Trevor Olson, James Amos The presentation reports the recent progress made on reliable signal recording and processing using 3-color broadband coherent Raman scattering (3C-BCRS). Signals are generated either from nanoparticle structures on surfaces or from bulk samples in transmission and in epi-detected mode. Spectra are recorded with a narrowband (at 532 nm) and a broadband radiation produced by a newly optimized optical parametric oscillator using the signal or idler beams. Vibrational and librational bands are measured over the 0.15-15 THz spectral range from solution and crystalline samples. Volumetric Brag-filter approach is introduced for recording 3C-BCRS spectra at the first time. The technical limitations and advantages of the narrowband filtering relative to the Notch-filter technic is clarified. The signal is proportional to the spectral autocorrelation of the broadband radiation therefore the present scheme gives a better signal-to-noise ratio relative to the traditional multiplex CRS methods. This makes the automation of non-model dependent signal processing more reliable to extract vibrational information which is very crucial in coherent Raman microscopy. [Preview Abstract] |
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T1.00349: Growth and Structural Characterization of RuO$_{\mathrm{2}}$/VO$_{\mathrm{2}}$ Bilayers for Tunneling Spectroscopy Ali Amiri, Josh Jones, Patrick LeClair, Arunava Gupta Vanadium dioxide is one of the most studied oxides for its sharp metal to insulator transition near room temperature (340 K). Various experimental and theoretical approaches are still going on to make a proper and comprehensive understanding of this transition. Heterostructures of VO$_{\mathrm{2}}$ and RuO$_{\mathrm{2}}$ are of interest for tunneling studies. The purpose of this experiment is to study the transport properties of VO$_{\mathrm{2}}$ far below the metal-insulator transition temperature (MIT). This will make it possible to understand the nature of the ground state and to investigate the excitations in VO$_{\mathrm{2}}$ strongly correlated electron system. To make these heterostructures, the epitaxial films of RuO$_{\mathrm{2}}$ are grown on TiO$_{\mathrm{2}}$ (100) substrates. Subsequently, an epitaxial VO$_{\mathrm{2}}$ film is grown in-situ on RuO$_{\mathrm{2}}$. Both films are grown in a low pressure chemical vapor deposition system. The structural characterization by XRD confirms the epitaxial growth. The morphology studies by atomic force microscopy show a smooth film with about 1nm of roughness. Finally, the resistance measurement versus temperature demonstrates the superposition of the transport behaviors of these two isostructural films. [Preview Abstract] |
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T1.00350: Capacitance in nanoscale bulk-heterojunction materials Nelson Coates In their simplest form, capacitors can be thought of as geometric devices consisting of two conductors separated by an insulator. These two conductors can hold opposite charges, and as a result store energy in the region of electric field between them. The geometric capacitance of the most basic parallel-plate conductor geometry is defined as: $C_{geom} =\frac{\varepsilon A}{d}$ where $A $is the area of the conducting plates, $d $ is the separation distance between the two plates, and $\varepsilon $ is the electric permittivity of the insulator between the two plates. This parallel plate geometry can operate as a useful approximation for devices where the separation distance between two conductors is much smaller than their curvature or area. A promising way to achieve this geometry is with nanoscale bulk-heterojunctions (including both purely organic, and organic-inorganic composites) which combine conducting phases with an enormous interfacial area and very small separation. The formation of these morphologies has been studied to improve the efficiencies of technologically relevant devices such as solar-cells and radiation detectors, where the capacitance provides useful information about electron-hole recombination and transport. Here, we will extend these studies to explore bulk-heterojunction morphologies as a platform for capacitive energy storage. [Preview Abstract] |
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T1.00351: Ground State Hedgehog Skyrmion Bubbles in Ultrathin Heterostructures with Interfacial Dzyaloshinskii-Moriya Interactions Javier Pulecio, Aleš Hrabec, Katharina Zeissler, Ryan White, Yimei Zhu, Christopher Marrows Isolating magnetic skyrmions in their ground state, mapping the topology and understanding the related topological effects is of great interest. Here we experimentally investigate the effect of dipolar energy from interlayer coupling on the remanent spin textures found at room temperature for interfacial DMI multilayers of [ Pt $\backslash $ Co $\backslash $ Ir ]$_{\mathrm{\times }}_{N}$. The total dipolar energy is modified by increasing the number of layer repetitions $N$ which result in different phases of chiral magnetic textures [1]. The films exhibit isolated hedgehog skyrmion bubble phase, as well as a sub 100 nm labyrinth domain phase with cycloidal homochiral N\'{e}el walls in zero field. By tuning the total dipolar energy, stabilize the skyrmion bubble phase as a ground state. The circular skyrmion bubbles in continuous films can be inflated to various sizes and take up an irregular shape above a critical size [2]. [1] Pulecio, J. F. \textit{et al}. Hedgehog Skyrmion Bubbles in Ultrathin Films with Interfacial Dzyaloshinskii-Moriya Interactions, 12. Materials Science. ArXiv ID: 1611.06869 [2] Pulecio, J. F. \textit{et al.} Phase Transitions of Chiral Spin Textures via Dipolar Coupling in Multilayered Films with Interfacial DMI. ArXiv ID: 1611.00209 [Preview Abstract] |
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T1.00352: Modeling and experiments for fractional-wet rhomboidal pores Rahul Verma, Sriram Chandrasekhar, Masha Prodanovic, Kishore Mohanty Wettability is commonly expressed as the contact angle that fluid interfaces form with a solid surface in the presence of another fluid. For multiphase flow in porous media, pore-scale wetting behavior controls the movement of fluid-fluid interfaces and can significantly alter macro-scale properties like capillary pressure and relative permeability. Fractional wettability of soil (where grains are a mixture of hydrophilic and hydrophobic) is common, as is its counterpart in rocks called mixed wettability. Wettability behavior may be intrinsic, or brought about by extreme conditions such as wildfires or presence of non-aqueous contaminants. Modeling fractional-wet systems at the pore-scale should reveal insights into different phenomena like trapping of phases and hysteresis in capillary pressure-saturation curves. Validation of tools is important as modeling the moving contact line is not a trivial computational task, alas lack of analytical models makes it difficult. In this work, we conduct experiments to determine threshold capillary pressures for drainage in rhomboidal arrangements of fractional-wet spheres. We then use the level-set method based model of capillarity dominated displacement to model this system. [Preview Abstract] |
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T1.00353: Holistic computational structure screening of more than 12,000 candidates for solid lithium-ion conductor materials Austin D. Sendek, Qian Yang, Ekin D. Cubuk, Karel-Alexander N. Duerloo, Yi Cui, Evan J. Reed We present a new type of large-scale computational screening approach for identifying promising candidate materials for solid state electrolytes for lithium ion batteries that is capable of screening all known lithium containing solids. To predict the likelihood of a candidate material exhibiting high lithium ion conductivity, we leverage machine learning techniques to train an ionic conductivity classification model using logistic regression based on experimental measurements reported in the literature. This model, which is built on easily calculable atomistic descriptors, provides new insight into the structure-property relationship for superionic behavior in solids and is approximately one million times faster to evaluate than DFT-based approaches to calculating diffusion coefficients or migration barriers. We couple this model with several other technologically motivated heuristics to reduce the list of candidate materials from the more than 12,000 known lithium containing solids to 21 structures that show promise as electrolytes, few of which have been examined experimentally. Our screening utilizes structures and electronic information contained in the Materials Project database. [Preview Abstract] |
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T1.00354: Develop of a quantum electromechanical hybrid system YU HAO, Francisco Rouxinol, Frederico Brito, Amir Caldeira, Elinor Irish, Matthew LaHaye In this poster, we will show our results from measurements of a hybrid quantum system composed of a superconducting transmon qubit-coupled and ultra-high frequency nano-mechanical resonator, embedded in a superconducting cavity. The transmon is capacitively coupled to a 3.4GHz nanoresonator and a T-filter-biased high-Q transmission line cavity. Single-tone and two-tone transmission spectroscopy measurements are used to probe the interactions between the cavity, qubit and mechanical resonator. These measurements are in good agreement with numerical simulations based upon a master equation for the tripartite system including dissipation. The results indicate that this system may be developed to serve as a platform for more advanced measurements with nanoresonators, including quantum state measurement, the exploration of nanoresonator quantum noise, and reservoir engineering. [Preview Abstract] |
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T1.00355: Studies of Glass vs Crystal Forming Abilities and other Far-From-Equilibrium Phenomena Using Machine Learning Wade Fuerste, Yang Zhang Far-from-equilibrium reactions and processes have been long known to exist, but the quantitative understanding of these phenomena have been challenging. This is partly due to their diverse range of timescales that are occurring out of the range of existing methods. Previous attempts to quantify this area of research have fallen short due the large computational costs or accurate measurements at the molecular level over second, and larger, timescales. Our group exploits a range of non-equilibrium processes all containing large scale fluctuations and heterogeneity. We aim to develop and apply machine learning algorithms, built upon molecular simulations, to sample statistically rare events efficiently and understand the long timescale phenomena from the molecular level. With machine learning we analyzed large sets of data, beyond standard computational means, to gain a more accurate understanding of these far-from-equilibrium processes. Herein, we will show new insights provided by machine learning analysis on the dynamics of supercooled liquids and glasses, nucleation and crystal growth rates. [Preview Abstract] |
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T1.00356: A Universal Phase in minimal 3D embedding of Networks Nima Dehmamy, Soodabeh Milanloui, Albert-Laszlo Barabasi Analyzing networks embedded in 3D space is crucial for understanding brain anatomy and pathologies pertaining to physical connections in the brain. Devising physical 3D layouts for networks is also of interest for visualization purposes. Additionally, given the recent advancements in 3D printing technology, efficient and economical 3D layouts may have practical value in design and manufacturing of complex devices. The role of network topology in layouts and the limitations it imposes on the feasibility of layouts must, thus, be studied. We develop a minimal 3D layout algorithm for networks, inspired by force-directed layouts. We analyze the spatial properties of our layouts and find two phases based on link thickness and derive the phase transition criterion. In both phases, different network topologies turn out to be very similar in their volumetric properties and are not distinguishable based on volume. Relative link orientation, does differentiate the topologies when links are thin, but fails to do so at large link thickness. Thus, we discover a universal phase for 3D networks when link thickness is large. Comparing against brain literature, we find that rodent brains may be related to this universal phase at the level of connections between brain regions. [Preview Abstract] |
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T1.00357: Computational Design of Graphene Nanoscrolls. Karteek Bejagam, Samrendra Singh, Sanket Deshmukh Graphene nanoscrolls have obtained a significant interest in recent years due to their potential applications in tribology, nanotechnology, and bioengineering. For example, recently it has been shown that graphene nanoscrolls can be used to experience superlubricity -- almost zero friction state. In the present study we employ the metal/non-metal nanoparticles to facilitate the graphene nanoscroll formation. We have conducted reactive molecular dynamics (RMD) simulations of diamond, Nickel, and Gold nanoparticles placed on the 2D graphene sheet. RMD simulations reveal the mechanisms that facilitates or prohibits the graphene nanoscroll formation. Our simulations suggest that the surface chemistry and interactions between nanoparticles and graphene play a crucial in determining the mechanism of scroll formation and the nature of the nanoscroll. We also find that the type of a nanoparticle has strong influence on the elastic and mechanical properties of the nanoscroll. Our study provides a systematic pathway to design graphene nanoscrolls with a wide range of properties. [Preview Abstract] |
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T1.00358: Development of accurate potentials to explore the structure of water on 2D materials. Karteek Bejagam, Samrendra Singh, Sanket Deshmukh Water play an important role in many biological and non-biological process. Thus structure of water at various interfaces and under confinement has always been the topic of immense interest. 2-D materials have shown great potential in surface coating applications and nanofluidic devices. However, the exact atomic level understanding of the wettability of single layer of these 2-D materials is still lacking mainly due to lack of experimental techniques and computational methodologies including accurate force-field potentials and algorithms to measure the contact angle of water. In the present study, we have developed a new algorithm to measure the accurate contact angle between water and 2-D materials. The algorithm is based on fitting the best sphere to the shape of the droplet. This novel spherical fitting method accounts for every individual molecule of the droplet, rather than those at the surface only. We employ this method of contact angle measurements to develop the accurate non-bonded potentials between water and 2-D materials including graphene and boron nitride (BN) to reproduce the experimentally observed contact angle of water on these 2-D materials. Different water models such as SPC, SPC/Fw, and TIP3P were used to study the structure of water at the interfaces. [Preview Abstract] |
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T1.00359: Influence of Ta doping in resistive switching behavior of TiO$_{\mathrm{2}}$ Arabinda Barman, Chetan P Saini, Sujit Deshmukh, Sankar Dhar, Aloke Kanjilal An approach has been made to understand the resistive switching behavior in Ta-doped TiO$_{\mathrm{2}}$ films on Pt substrates. Prior to thin film deposition, Ta-doped TiO$_{\mathrm{2}}$ powder has been synthesized chemically using Ta and Ti precursor solutions. However, the Ta doping has seriously been affected by increasing Ta concentration above 1 at{\%} due to the segregation of Ta$_{\mathrm{2}}$O$_{\mathrm{5}}$ phase. The Ta-doped TiO$_{\mathrm{2}}$ targets have been prepared for pulsed laser deposition of the films on Pt substrates using an excitation wavelength of 248 nm. The structural and chemical properties of the Ta-doped TiO$_{\mathrm{2}}$ films have been investigated in details with the help of XRD, SIMS, XAS and XPS. The stoichiometry of the Ta-doped TiO$_{\mathrm{2}}$ films with increasing depth has been verified initially by SIMS. The electrical study of the corresponding device structures further suggests that the optimized resistive switching effect can be accomplished up to a threshold Ta-doping of 1 at{\%}. Nevertheless, a highly conducting behavior has been shown when the TiO$_{\mathrm{2}}$ films are doped with 2 at{\%} Ta. These results will be discussed in details in the light of defect induced resistive switching phenomenon. [Preview Abstract] |
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T1.00360: Computational Design of Epoxy/ Boron Carbide Nanocomposites for Radiation Shielding Applications. Karteek Bejagam, Nasim Galehdari, Ingrid Espinosa, Sanket A. Deshmukh, Ajit D. Kelkar An individual working in industries that include nuclear power plants, healthcare industry, and aerospace are knowingly or unknowingly exposed to radiations of different energies. Exposure to high-energy radiations such as $\alpha $/$\beta $ particle emissions or gamma ray electromagnetic radiations enhances the health risks that can lead to carcinogenesis, cardiac problems, cataracts, and other acute radiation syndromes. The best possible solution to protect one from the exposure to radiations is shielding. In the present study, we have developed a new algorithm to generate a range of different structures of Diglycidyl Ether of Bisphenol F (EPON 862) and curing agent Diethylene Toluene Diamine (DETDA) resins with varying degrees of crosslinking. 3, 5, and 10 weight percent boron carbide was employed as filling materials to study its influence on the thermal and mechanical properties of composite. We further conduct the reactive molecular dynamics (RMD) simulations to investigate the effect of radiation exposure on the structural, physical, and mechanical properties of these Epoxy/Boron Carbide nanocomposites. Where possible the simulation results were compared with the experimental data. [Preview Abstract] |
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T1.00361: Anderson Localization in Time-Dependent Hamiltonians Elizabeth Noelle Blose, Natasha Proctor, Rajiv Singh, Richard Scalettar We study a generalization of Anderson localization to show that different forms of time-dependence of onsite energies cause the system to behave in qualitatively different ways. Our results confirm the known result that random time dependence causes a disordered system to delocalize completely. However, we find that periodic time dependence causes an increase in localization length, but not complete delocalization. [Preview Abstract] |
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T1.00362: Positive impact of agglomeration in nanocomposite conductivity Taylor Tarlton, Ethan Sullivan, Pedro Derosa CNTs are embedded in an insulating matrix to form composites to improve its mechanical, thermal and electrical properties. However, CNTs tend to clump together forming agglomerates and thus Experimental studies on CNT composites normally describe significant effort in dispersing CNT for a more effective performance. Although the main concern is on the impact agglomeration has on mechanical strength, it is accepted that agglomeration will also negatively affect conductivity. In this workg computer simulations are used to study this effect in detail and it is found that some level of agglomeration actually improves conductivity by a better use of the available volume. Agglomerates leave voids in the sample in favor of other areas where the CNT-CNT distance is smaller than it would be if their distribution were uniform thus improving conductivity. More uniform samples have more conduction paths, but CNT-CNT distance is in average larger leading to a lower mobility. The opposite happen when some agglomeration is present and thus there is a tradeoff that above, but near, percolation leads to higher conductivity in the case where some agglomeration is present. At higher concentrations, the effect of mobility seems to be larger as there are enough conduction paths already available. [Preview Abstract] |
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T1.00363: Nonlinear and anisotropic strain in ultrafast laser-excited semiconductors Eric Landahl, G. Jackson Williams, Donald Walko, Sooheyong Lee We have used time-resolved x-ray diffraction to measure the lattice response of gallium arsenide and indium antimonide crystals following ultrafast laser absorption. Our studies use two modified approaches: measurement of multiple lattice planes and decomposition into principal axes using a strain rosette, and modulations of x-ray diffraction lineshapes by multiphoton processes. In contradiction to the common one-dimensional assumption of the Thomsen strain model (Phys. Rev. B 34, 4129–4138 (1986)), we find that anisotropic strain is responsible for a considerable fraction of the total lattice motion at early times in GaAs before thermal equilibrium is achieved. We also find that the initial linear expansion of the crystal stagnates at a laser fluence corresponding to the saturation of the free carrier density before resuming expansion in a third regime at higher fluences where two-photon absorption becomes dominant. We therefore claim to be able to visualize anisotropic and nonlinear optical effects directly in the dynamic structure of these materials. [Preview Abstract] |
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T1.00364: Active Control of Charge Density Waves at Degenerate Semiconductor Interfaces Raj Vinnakota, Dentcho Genov We present numerical modeling of an active electronically controlled highly confined charge-density waves, i.e. surface plasmon polaritons (SPPs) at the metallurgic interfaces of degenerate semiconductor materials. An electro-optic switching element for fully-functional plasmonic circuits based on p-n junction semiconductor Surface Plasmon Polariton (SPP) waveguide is shown. Two figures of merits are introduced and parametric study has been performed identifying the device optimal operation range. The Indium Gallium Arsenide (In$_{\mathrm{0.53}}$Ga$_{\mathrm{0.47}}$As) is identified as the best semiconductor material for the device providing high optical confinement, reduced system size and fast operation. The electro-optic SPP switching element is shown to operate at signal modulation up to -24dB and switching rates surpassing 100GHz, thus potentially providing a new pathway toward bridging the gap between electronic and photonic devices. [Preview Abstract] |
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T1.00365: Investigation of electronic and morphological changes from thionation of naphthalene diimide (NDI) adam welford, Chris McNeill, Subashani Maniam Organic semiconductors (OSCs) possess many inherent advantages that allow them to be used effectively as organic field effect transistors (OFETs). Solution processablility allows rapid, large area fabrication on low cost flexible substrate that make them ideal for specialized applications such as flexible displays and radio frequency identification (RFID). \newline Small molecule OSCs provide chemical specificity that allows changes to be mapped and examined more effectively than polymer based OSCs. Naphthalene diimide (NDI) provides a versatile framework with which to build upon and explore the effects of chemical functionalization. Recent work on a small molecule framework from the same chemical family has shown that substitution of oxygen for sulphur, known as thionation, leads to an increase in crystallinity and an electron mobility. A thionated series of NDI OSCs has been synthesized to examine the effects of increased degrees of thionation on optical, electronic and morphological properties. Investigation via the complimentary synchrotron based techniques of near edge x-ray absorption fine structure (NEXAFS) spectroscopy and grazing incidence wide angle xray scattering (GIWAXS) combine with atomic force microscopy (AFM) and top gate bottom contact (TGBC) transistors to help illuminate the resulting changes of the top interface with increasing degrees of thionation. \newline [Preview Abstract] |
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T1.00366: Crises as instabilities in an effective theory model of market response Nima Dehmamy, Sergey Buldyrev, Shlomo Havlin, Eugene Stanley, Irena Vodenska We show that effective Lagrangian modeling of fluctuations in a market network plus dissipation explains a phenomenological model previously introduced by us. Our results suggested that the model identified the time-line of the 2009-2011 Eurozone crisis correctly. Assuming sparsity of connections -- which holds for Eurozone crisis -- we derive analytically derive the phases and where the phase transition happens. We show that this model has three distinct phases that can broadly be categorized as ``stable'' and ``unstable''. Based on the interpretation of our behavioral parameters, the stable phase describes periods where investors and traders have confidence in the market (e.g. predict that the market rebounds from a loss). We show that the unstable phase happens when there is a lack of confidence and seems to describe ``boom-bust'' periods in which changes in prices are exponential. [Preview Abstract] |
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T1.00367: Hall devices based on transfer print of CVD graphene onto 75$\mu $m-thick PVC film via lamination Ugur Inkaya, Ahmet Oral Having high mobility even for low density of charge carriers and large tensile strength, graphene is a favorable material for the fabrication of flexible Hall sensors. Laminating graphene obtained on 20$\mu $m-thick Cu foil via atmospheric-pressure CVD with 75$\mu $m-thick PVC film, we developed a simple and low-cost scheme for manufacturing graphene-based flexible Hall devices, without resorting to metallization techniques such as evaporation or sputtering. Instead of these techniques, electrical contacts are provided by the pieces of copper foils preserved during the chemical etching with an aqueous solution of ferric chloride. By using this scheme, we manufactured 95$\mu $m-thick flexible Hall sensors with resistances and Hall coefficients of the order of 1 k$\Omega $ and 100 $\Omega $/T. Moreover, we made Hall devices by iterating our manufacture scheme multiple times, thereby forming few- or multi-layer graphene and hence we were able to both observe the dependence of the characteristics of the Hall sensors upon the number of graphene layers and characterize the resulting graphene structures. The fabrication and the characterization of the 95$\mu $m-thick flexible Hall sensors, and the characterization of the multi-layer graphene will be presented. [Preview Abstract] |
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T1.00368: Thermal magnetic relaxation in sub-100nm square artificial spin ice systems measured by SQUID magnetometry Jose Maria Porro Azpiazu, Sophie Morley, Christopher Marrows, Sean Langridge Artificial spin-ice systems (ASI) are lithographically defined patterns of ensembles of interacting ferromagnetic nanomagnets with bistable single-domain behaviour of the magnetization, arranged in geometries that mimic the magnetic frustration present in spin-ice materials. In the square ASI, each vertex has four nanomagnets whose magnetic moment points either in or out. The lowest energy arrangement consists of two-in and two-out, obeying the ‘ice-rule’. We studied the magnetic relaxation of thermally active square ASIs made of Permalloy (NiFe), formed by nanomagnets with dimensions 70x22x6nm3 covering 2mm2, by SQUID magnetometry. We have investigated the effect of the interaction strength, by varying the lattice spacings; and of the oxidation of the Permalloy. We observed that for higher interaction strength the relaxation times decrease to lower temperatures, and that the oxidation does not affect the dynamics other than decreasing the interaction strength due to a reduction of the volume of the nanomagnets. This gives us a way to quantify the effective lowering of the reversal barrier of the individual islands due to the field it experiences from its neighbours. This is compared to the interaction energy as calculated from a simple dipole model and micromagnetic simulations. [Preview Abstract] |
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T1.00369: Effects of Horn Ellipticity and Eccentricity on Neutrino Flux for DUNE Eric Amador, Jaehoon Yu, Paul Lebrun, Monica Avila, Nicholas Lira We will simulate the effects of horn ellipticity, eccentricity and current equalizer on our horn focusing system for the Deep Underground Neutrino Experiment (DUNE). The muon neutrino and electron neutrino integrated fluxes will be measured at both Near and Far Detector, and will be compared to its anti-neutrino mode integrated fluxes. [Preview Abstract] |
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T1.00370: Beta Particle Detection Using a Gas Electron Mutiplier Monica Avila, Jaehoon Yu, Joshua Medford, Eric Amador, Nick Lira My current research focuses on beta particle detection by electron amplification using a Gas Electron Multiplier (GEM). This study revolves around the GEM detector itself, and how its geometry affects gain. In my research, this includes utilizing both a two and three layer detector. By using beta decay as a source, I can create a avalanche effect in the detector which proceeds to create a signal. The argument remains wether an extra gem foil layer and detector is a key factor in results. [Preview Abstract] |
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T1.00371: Hierarchical abstraction of information in Deep Neural Networks Nima Dehmamy, Neda Rohani, Aggelos Katsaggelos We develop a theoretical framework for how hierarchical representation of features in input data emerges from progressive renormalization and sparse-coding done using convolutional layers. At each level new degrees of freedom appear, which are low-lying energy states, separated by a gap from a pool of high energy states. This separation defines a natural way for sparse encoding of training data. Repeating this renormalization procedure results in a hierarchical representation of the data. We show that trained filter in popular image processing deep neural nets are consistent with such a hierarchical representation. [Preview Abstract] |
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T1.00372: Calculation of the local electric field at the CNT-CNT junction in a nanocomposites Ethan Sullivan, Taylor Tarlton, Pedro A Derosa The use of composite materials with an insulating matrix and a conductive filler have seen intense study in recent years. The insertion of the conductive phase creates materials that can be useful for applications ranging from electromagnetic interference shielding to structural health monitoring purposes. In modeling charge transport in nanocomposties, a work assumption made by these authors (as well others) is that the electric field in all CNT-CNT junctions is the same, and assumption that may not be correct. This study looks closely at the behavior of the local electric field within the composite upon applying a voltage bias in a 3D system using finite element analysis, paying particular attention to the electric field in the CNT-CNT junction, something that has so far been neglected in the literature. Conduction in composites is controlled by the transport at those junctions and thus its characterization is required to understand the overall transport process. [Preview Abstract] |
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T1.00373: Production of Hyper-Doped Silicon at Greater than One Atmosphere of Sulfur Hexafluoride Daniel Weisz, John Testerman, Reni Ayachitula, Kimberly de La Harpe We demonstrate the successful processing of sulfur-hyper-doped silicon using a nanosecond-pulsed laser in the presence of sulfur hexafluoride at pressures greater than one atmosphere. At these pressures, microstructures that form on the surface contain comparable sulfur content as samples processed traditionally at pressures less than 1 atm but require less energy to form. Samples with these structures were verified to have enhanced absorption into the infrared spectrum making them of interest for solar cell and infrared detection technologies. [Preview Abstract] |
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T1.00374: Flat Band Emerging from the Exceptional Point of a PT Symmetric System Hamidreza Ramezani Controllable and yet robust confinement of light is vital for many applications. Flat bands induced by symmetries are proposed for robust localization of light. Here we show that localization arises at the exceptional point, where by breaking the parity-time symmetry and without entering to the broken phase a flat band is generated. Although the system is not in the exact phase, the localized field intensity remains conserve. The number of sites needed to accommodate the nondispersive mode of infinite lattice is four. The localization is robust against the changes in the system size and remains unperturbed even by reducing the system size to four coupled waveguides. The generated flat band is embedded in the dispersive bands. Consequently, it has infinite modes that can be considered as bound state in continuum. The exceptional point induced flat band provides a route for controllable light localization using active materials and new opportunities in imaging via gain and loss mechanism. [Preview Abstract] |
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T1.00375: Wave-current interactions in ultra-subwavelength plasmons Jingyee Chee, Ling Qin, Jundong Wu, Donhee Ham The low dimensionality of 2D conductors such as semiconductor quantum wells, graphene, and transition metal dichalcogenides, enables them to exhibit intriguing fundamental phenomena such as ultraslow plasmons. Our group has previously obtained 2D plasmons with very low phase velocities of less than $c / 500$ in GaAs / AlGaAs heterostructures. These ultraslow plasmons open up new exciting vistas for solid-state terahertz technology by enabling ultra-subwavelength light manipulation and strong light-matter interaction. In fact, our group has developed a broad variety of ultra-subwavelength 2D plasmonic circuits at GHz-THz frequencies, which include plasmonic bandgap crystals and interferometers. This poster presentation will first review this prior work and subsequently describe our on-going effort to observe and exploit the wave-current interaction of these plasmonic waves to form irreciprocal transmission lines. We directly measure this irreciprocity in a HEMT structure using a network analyzer, and found the phase delay difference between the forward and backward waves to be greater than $0.10^{\circ}$ per um at 50 GHz. We will also describe our attempts to measure amplification associated with the irreciprocity. [Preview Abstract] |
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T1.00376: Temperature dependent terahertz properties of Ammonium Nitrate Abdur Rahman, Abul Azad, David Moore Terahertz spectroscopy has been demonstrated as an ideal nondestructive method for identifying hazardous materials such as explosives. Many common explosives exhibit distinct spectral signatures at terahertz range (0.1-6.0 THz) due to the excitations of their low frequency vibrational modes. Ammonium nitrate (AN), an easily accessible oxidizer often used in improvised explosive, exhibits strong temperature dependence. While the room temperature terahertz absorption spectrum of AN is featureless, it reveals distinct spectral features below 240 K due to the polymorphic phase transition. We employed terahertz time domain spectroscopy to measure the effective dielectric properties of AN embedded in polytetrafluoroethylene (PTFE) binder. The dielectric properties of pure AN were extracted using three different effective medium theories (EMT), simple effective medium approach, Maxwell-Garnett (MG) model, and Bruggeman (BR) model. In order to understand the effect of temperature on the dielectric properties, we varied the sample temperature from 5K to 300K. This study indicates presence of additional vibrational modes at low temperature. These results may greatly enhance the detectability of AN and facilitate more accurate theoretical modeling. [Preview Abstract] |
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T1.00377: Nanodomain Swelling of Water-Equilibrated Block Copolymer Electrolyte Membranes Chelsea Chen, Xi Jiang, Nitash Balsara In this work, we examine the nanoscale swelling behavior of block copolymer electrolytes immersed in liquid water. A series of sulfonated polystyrene-$b$-polyethylene-$b$-polystyrene (S-SES) membranes having the same chemical composition but with different morphologies are prepared. We use small angle X-ray scattering (SAXS), cryogenic scanning transmission electron microscopy (cryo-STEM) and cryogenic electron tomography to characterize the nanodomain swelling of S-SES membranes. The relative increase of the nanodomain size upon hydration shows a transition which coincides with a morphological transition from lamellar to bicontinuous morphology. The nanodomain swelling of S-SES membranes with bicontinuous morphology is smaller than that of S-SES membranes with lamellar morphology while the water uptake is much larger. Electron tomography revealed that swelling of the membrane with bicontinuous morphology was spatially isotropic, which is the origin of the smaller relative domain size increase compared to the lamellar membranes whose swelling is anisotropic. [Preview Abstract] |
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T1.00378: The Investigation of Laser Ignited Plasma with the Application of Current Probes Trevor Olsson, James Amos, Laszlo Ujj Among a variety of atomic emission spectroscopy methods Laser-induced breakdown spectroscopy (LIBS) is the one which can analyze any solid, liquid or gas sample. The elemental composition and the relative abundance of the constituent elements in the samples can be determined when the emission spectra of short laser pulses igniting plasma is then recorded and analyzed(e.g.). In our studies we have made a LIBS system which includes, but is not limited to investigating the physical phenomena and properties of the emitting plasma. Active research is going on concerning Lithium-ion batteries to increase the stored charge and energy per volume properties of the device. LIBS is proposed to test the manufacturing process and analyze the chemical constituents of the newly developed batteries. The composition of the battery itself consists of two pieces of foil, typically aluminum and copper acting as a cathode and anode respectively. Separating these two pieces of foil is a lithium based compound. The general chemical composition is Lix [Metal]y Oz where [Metal] is the specific element that is used to achieve the purpose of the battery (one metal may increase the out-put while another helps with capacity etc.). We have chosen the Li-Ion battery composed of LiCoO2 from a mobile phone in order to investigate the Stark-effect (Stark shift and Stark broadening) of the lithium present in the sample. Effects of line broadening and reabsorption of the signals are addressed by recording LIBS spectra from the powder electrolyte extracted from a Lithium-ion battery. [Preview Abstract] |
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T1.00379: Theoretical Study of Chemisorption on GaAs Clusters. Alexandra Valdez, Ajit Hira, Ruben Rivera, Amberly Maes We extend our work on the theoretical study of molecular clusters in this report on the chemical properties of small Ga$_{\mathrm{n}}$As$_{\mathrm{n}}$ clusters (n $=$ 2 - 14). We study the chemisorption of different atomic and molecular species on small clusters of semiconducting elements, by examining the interactions of O$_{\mathrm{2}}$, O$_{\mathrm{2,}}$ Li, and Be adsorbates with the GaAs clusters. Semiconductor clusters are of interest for the understanding of quantum size effects and of metallization phenomena. Hybrid ab initio methods of quantum chemistry (particularly the DFT-B3LYP model) were used to derive optimal geometries for the clusters of interest. We compared calculated binding energies, bond-lengths, ionization potentials, electron affinities, and HOMO-LUMO gaps for these clusters. Mapping of the singlet, triplet, and quintet, potential energy surfaces was performed. Implications for fundamental mechanisms of atomistic assembly on the GaAs surfaces will be examined. Applications to the manufacture of GaAs nanowires will be presented. [Preview Abstract] |
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T1.00380: DNA-binding drug screening by novel palladium nano-crystalline electrod Wei Chen, Chien-Hao Su, Guo-Cheng Hsu, Chia-Ching Chang The interaction between DNA and small molecule is one of the key issue in drug discovery and pharmaceutical development. Recently, the technique using electrochemistry impedance spectroscopy (EIS) to detect drugs and DNA interaction are widely used However, both operability and sensitivity of conventional electrode probes are low. However, by using novel nanocrystalline palladium (Pd) film electrode both usability and sensitivity increased Therefore, a Pd nano-thin film electrode was used in anticancer drugs and DNA interaction detection. The DNA sequence specificity of the anticancer drug has been demonstrated and the sensitivity is as sensitive as sub nano-gram level. Therefore, we have demonstrated the potential usage of this nanocrystalline palladium (Pd) film electrode in DNA binding drug screening. [Preview Abstract] |
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T1.00381: Physical Analysis of the Biomolecules Causing Periodontitis Jehun Shin, Seong Hyeon Lee, Chai Rin Kim Periodontitis caused by microorganisms that adhere to and grow on the tooth's surfaces, is an inflammatory diseases causing gum infection. The disease damages the soft tissues that surround and support the teeth and destroys the bone that supports teeth and finally causes tooth loss. An increased risk of stroke and heart attack problems are related to the periodontitis as well. Most bacteria or pathogens attach to gum surface where they form a biofilm. Bacterial cells in biofilms are well protected against antibiotics. The mechanisms of action are still unknown, and it is difficult to control pathogens with antibiotics in biofilm infections and thus the study on the antibiotics is needed. In this research, a number of natural water soluble, small-sized antibiotics molecules and their derivatives are studied. Molecular editing programs such as Gamess, Chemcraft and Avogadro, with an auto-optimization feature that determines the theoretical values of the structure’s atomic properties are used to build virtually any molecule with the optimized geometry according to various force field options. The UFF (Universal Force Field) is used for optimizing most molecules. [Preview Abstract] |
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T1.00382: Biochemical Stability Analysis of Nano Scaled Contrast Agents Used in Biomolecular Imaging Detection of Tumor Cells Jennifer Kim, Richard Kyung Imaging contrast agents are materials used to improve the visibility of internal body structures in the imaging process. Many agents that are used for contrast enhancement are now studied empirically and computationally by researchers. Among various imaging techniques, magnetic resonance imaging (MRI) has become a major diagnostic tool in many clinical specialties due to its non-invasive characteristic and its safeness in regards to ionizing radiation exposure. Recently, researchers have prepared aqueous fullerene nanoparticles using electrochemical methods. In this paper, computational simulations of thermodynamic stabilities of nano scaled contrast agents that can be used in biomolecular imaging detection of tumor cells are presented using nanomaterials such as fluorescent functionalized fullerenes. In addition, the stability and safety of different types of contrast agents composed of metal oxide a, b, and c are tested in the imaging process. Through analysis of the computational simulations, the stabilities of the contrast agents, determined by optimized energies of the conformations, are presented. The resulting numerical data are compared. In addition, Density Functional Theory (DFT) is used in order to model the electron properties of the compound. [Preview Abstract] |
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T1.00383: Study of the Pressure and Velocity Across the Aortic Valve Seo Young Kyung, Erica Soyun Chung, Joo Hee Lee, Hayoung Kyung, Si Young Choi Biomechanics of the heart, requiring an extensive understanding of the complexity of the heart, have become the interests of many biomedical engineers in cardiology today. In order to study aortic valve disease, engineers have focused on the data obtained through bio-fluid flow analysis. To further this study, physical and computational analysis on the biomechanical determinants of blood flow in the stenosed aortic valve have been examined. These observations, along with the principles of cardiovascular physiology, confirm that when blood flows through the valve opening, pressure gradient across the valve is produced as a result of stenosis of the aortic valve. The aortic valve gradient is used to interpret the increase and decrease on each side of the defective valve. To compute different pressure gradients across the aortic valve, this paper analyzes Aortic Valve Areas (AVA) using simulations based on the continuity equation and Gorlin equation. The data obtained from such analysis consist of patients in the AS category that display mild Aortic Valve Velocity (AVV) and pressure gradient. Such correlation results in the construction of a dependent relationship between severe AS causing LV systolic dysfunction and the transaortic velocity. [Preview Abstract] |
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T1.00384: Energetic contributions of DNA plectoneme tips and tails Keir Neuman, Andrew Ditmore Global DNA topology is sensed locally by enzymes that act on plectonemes in supercoiled DNA. Here we report that the formation and diffusion of plectonemes are determined by the energetic contributions of their tips and tails. First, to systematically vary the formation energy of plectoneme end-loops, we introduced base-pair defect regions of variable size (1-16 bp) at a specific site in a DNA substrate. Direct manipulation measurements with magnetic tweezers revealed that even a single mismatch is sufficient to nucleate formation of a plectoneme. Presentation of the defect at an extruded plectoneme tip potentially serves as a damage-sensing mechanism and may facilitate the search process of repair enzymes. Second, our measurements unexpectedly revealed that after DNA buckles into an initial plectoneme loop, further plectoneme extrusion occurs through a cascade of additional buckling steps. These discrete steps do not match any obvious scale of the system but are consistent with discontinuous feed-in of curving plectoneme tails. In light of these results, theoretical models of plectonemes should include their overall structure, including the often neglected tips and tails. [Preview Abstract] |
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T1.00385: Twisted Boundary Conditions for Lattice Monte Carlo Simulations Joseph Paki, Emanuel Gull Numerical simulations of spatially correlated lattice models have made progress via Dynamical Mean Field Theory and extensions such as the Dynamical Cluster Approximation, but are still hindered by computational costs that scale exponentially with lattice size. This presents a major barrier for applying modern many-body methods for correlated systems to real materials due to finite size errors. We present a method of addressing finite size errors in a computationally efficient manner by running simulations with twisted boundary conditions. The method is implemented with a continuous-time auxiliary spin impurity solver that Monte Carlo samples an interaction expansion series. Averaging over the twisted boundary conditions allows for thermodynamic extrapolation of certain physical quantities of interest without the cost associated with large system simulations. [Preview Abstract] |
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T1.00386: Photonic modulations of strongly correlated phenomena in complex oxides Yi-De Liou, Wen-Yen Tzeng, Heng-Jui Liu, Chih-Wei Luo, Yi-Chun Chen, Ying-Hao Chu, Jan-Chi Yang The interplays of lattice, charge, orbital, and spin degrees of freedom in strongly correlated oxides result in a broad spectrum of intriguing functionalities. Researches have been enthusiastically devoted to the advanced modulation of these intriguing phenomena via external stimuli. In this work, a core novel material, strontium iridates (SrIrO3), which exhibits giant photostriction under light illumination is successfully developed. SrIrO3 thin film was deposited by pulsed laser deposition, by which a layer-by-layer growth mode can be well tuned. The atomic-flat surface and high quality epitaxy have been distinguished by AFM and HR-XRD. XAS has been used to characterize the valence state as well as the electronic structure of SrIrO3. Power-dependent Raman spectroscopy reveals that SrIrO3 shows a huge lattice change (\textasciitilde 1.5 {\%}) under green laser illumination. We also studied ultrafast dynamics and photo-induced mechanical strain of SrIrO3 by dual-color transient reflectivity measurements. Through the fabrication of epitaxial heterostructures, we can elegantly transfer the photo-induced mechanical strain to the strongly correlated systems which grown on SrIrO3 layer, resulting in novel photonic modulations of correlated phenomena in complex oxides. [Preview Abstract] |
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T1.00387: Nonlinear optical effects in semi-polar GaN micro-cavity emitter Sween Butler, Hongxing Jiang, Jingyu Lin, Arup Neogi Nonlinear optical (NLO) response of low dimensional emitters is of current interest because of the need for active elements in photonic applications. NLO effects in a selectively grown array of semi-polar GaN microcavity structures offer a promising route toward devices for integrated optical circuitry in optoelectronics and photonics field. Localized spatial excitation of a single hexagonal GaN microcavity with semipolar facets formed by selective area growth was optimized for nonlinear optical light generation due to second harmonic generation (SHG) and multi-photon luminescence(MPL). Multi-photon transition induced by tightly focused femtosecond NIR incident field results in ultra-violet and yellow luminescence for excitations above and below half bandgap energy, whereas SHG was observed for below half bandgap energy. We show that color and coherence of the light generation from the emitter can be controlled by selective onset of the nonlinear process which depends not only on the incident laser energy and intensity but also on the geometry of the microcavity. Quasi-WGM like modes were observed for off-resonant excitations from the GaN microcavity resulting in enhanced SHG. The directionality of MPL and SHG will be presented as a function of the pump polarization. [Preview Abstract] |
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T1.00388: Temperature Dependence of Kinetic Inductance in a WSi Superconducting Nanowire Single-Photon Detector Kathryn L. Nicolich, Clinton T. Cahall, Gregory P. Lafyatis, Jungsang Kim, Daniel J. Gauthier, M. S. Allman, V. Verma, Sae Woo Nam There is currently great interest in developing detectors for efficiently measuring single photons for applications in quantum information science. One appealing platform is the superconducting nanowire single-photon detector (SNSPD). Here, a single photon absorbed by a nanowire of superconductor causes a region of the wire to transition to the normal (nonsuperconducting) state, which can be sensed by passing a small current through the device. The timing jitter and reset time of the detector is related to the kinetic inductance ($L_k$) of the nanowire that arises from the ballistic motion of Cooper pairs through the device. Thus, it is important to understand how this inductance depends on device parameters, such as the current passing through the device as well as the temperature. Recent work has shown that $L_k$ diverges when the nanowire is heated to $T_c$, which has implications in the development of novel superconducting devices. Here, we measure $L_k$ for various temperatures in a WSi SNSPD by fitting the falling edge of measured single-photon pulses. [Preview Abstract] |
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T1.00389: Influence of Au and Al capping layers on the magnetic properties of Fe/(Ga,Mn)As bilayers studied by x-ray absorption spectroscopy A.M. Alsmadi, Y. Choi, X. Liu, J. K. Furdyna Molecular beam epitaxy grown Fe films on (Ga,Mn)As/GaAs(001) substrates and capped with Au or Al thin over layers with different thicknesses were studied using element specific x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD). The x-ray measurements were carried out at the APS of Argonne National Lab. The optimization of thickness of the capping layer is an important issue as it must be thick enough to effectively protect the sample from oxidation. On the other hand, it must also give acceptably low signal attenuation in the capping layer especially for the XMCD measurements. For Au thicknesses up to 1.71 nm, we observed an antiferromagnetic Fe-oxide layer at the Fe/Au interface. On the other hand, Al thickness of 1.23 nm was enough to effectively protect the sample from oxidation in the air. The presence of antiferromagnetic FeO layer at the Fe/Au interface results in observing exchange bias (EB) phenomena in the Au/Fe/(Ga,Mn)As/GaAs. The presence of this EB helps us to study the coupling between Fe and (Ga,Mn)As layers and also to identify the physical properties of the interfacial layer at the Fe/(Ga,Mn)As interface. We observed an induced magnetic order in the (Ga,Mn)As layer at room temperature, which is ferromagenically coupled with the Fe layer. [Preview Abstract] |
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