Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session H71: Poster Session II (2:00pm - 5:00pm)Poster Undergrad Friendly
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Room: Exhibit Hall C/D |
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H71.00001: CONDENSED MATTER PHYSICS
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H71.00002: WITHDRAWN ABSTRACT
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H71.00003: Hydrodynamic Transport in Near Magic Angle Twisted Bilayer Graphene Mohammad Zarenia, Indra Yudhistira, Shaffique Adam, Giovanni Vignale Using the semiclassical quantum Boltzmann theory and employing the Dirac model with twist angle-dependent Fermi velocity we obtain results for the electrical resistivity, the electronic thermal resistivity, the Seebeck coefficient, and the Wiedemann-Franz ratio in near magic angle twisted bilayer graphene, as functions of doping density (around the charge-neutrality-point) and modified Fermi velocity. The Fermi velocity-dependence of the relevant scattering mechanisms, i.e. electron-hole Coulomb, long-ranged impurities, and acoustic gauge phonons is considered in detail. We find a range of twist angles and temperatures, where the combined effect of momentum-non-conserving collisions (long-ranged impurities and phonons) is minimal, opening a window for the observation of strong hydrodynamic transport. Several experimental signatures are identified, such as a sharp dependence of the electric resistivity on doping density and a large enhancement of the Wiedemann-Franz ratio and the Seebeck coefficient. |
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H71.00004: Detecting superconductivity out-of-equilibrium Benedikt Fauseweh, Sebastian Paeckel, Alexander Osterkorn, Thomas Koehler, Dirk Manske, Salvatore Manmana Pump-probe experiments on cuprates and similar systems suggest the existence of a transient superconducting state far above the critical temperature. This poses the question how to reliably identify the emergence of superconductivity, out-of-equilibrium. In our contribution we investigate this point by studying the non-equilibrium dynamics in an extended Hubbard model and by computing various observables, which are used in theory and experiment to identify superconductivity. We specifically show, that the time-dependent optical conductivity is not sufficient to distinguish between a dynamical induced superconductor or an enhanced metallic state. In turn, we suggest to utilize time-resolved ARPES experiments in the two-particle channel to probe for superconducting signatures. |
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H71.00005: WITHDRAWN ABSTRACT
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H71.00006: WITHDRAWN ABSTRACT
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H71.00007: Stimulated electron-electron interaction in cavities Hongmin Gao, Frank Schlawin, Dieter Jaksch Electron interactions mediated by the exchange of virtual bosonic excitations form a central cornerstone in quantum many-body theory where they are responsible for many-body phases such as superconductivity [1,2]. More recently, interactions mediated by excitations with photonic character, such as exciton-polaritons [3,4] and transverse cavity photons [5] have also been tipped to lead to superconductivity. We propose a novel scheme to engineer stimulated electron interactions in any 2D electron system coupled to a cavity under driving. The interaction can be tuned to be attractive (or repulsive) and lead to Cooper instability at temperature up to ~1K. Our scheme opens up a new avenue for on-demand quantum material engineering. |
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H71.00008: First-principles study on the electronic structures of ternary TMDC alloys in monolayer and multilayer forms Jun Nara, WenTong Geng, Takahisa Ohno Transition metal dichalcogenides (TMDCs) have attracted great attention for their potential application in many fields including light-emitting diodes and photo detectors. The possibility in controlling the stacking sequence of different kind of TMDC layers by means of van der Waals epitaxy enables us to design novel materials through electronic structure engineering. Recently, two-dimensional lateral heterostructures have been successfully synthesized by Sahoo et al. [1], providing us a new freedom in heterostructure design other than sequential stacking. We have investigated the electronic structures of a monolayer and multilayers of ternary alloys made of Mo(1-x)WxS2 by using PHASE/0 [2], a first-principles electronic structure calculation code. We obtain a direct energy band gap whose width is smaller than both MoS2 and WS2. Details of the results will be given in the presentation. |
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H71.00009: Electronic states and Coulomb excitations of α-T3 zigzag nanoribbons Paula Fekete, Andrii Iurov, Godfrey Gumbs, Danhong Huang We have examined all possible non-equivalent types of edge terminations for pseoudospin-1 α-T3-based nanoribbons. Our results show that all of their fundamental electronic properties depend significantly on both the hopping parameter α and the particular geometry of their edge. For all non-equivalent edge terminations, we have calculated the electronic wave functions, Coulomb potential, and plasmon dispersion relations. We also report on the dependence of the plasmon dispersion on the electron doping concentration for zigzag edged nanoribbons. |
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H71.00010: Ultrafast nonlinear electron dynamics in gapped graphene Ahmal Zafar, Seyyedeh Azar Oliaei Motlagh, ARANYO MITRA, Fatemeh Nematollahi, Vadym Apalkov, Mark I Stockman
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H71.00011: Ultrafast field-driven currents in gapped graphene ARANYO MITRA, Seyyedeh Azar Oliaei Motlagh, Ahmal Zafar, Fatemeh Nematollahi, Vadym Apalkov, Mark I Stockman We study theoretically interaction of a linearly polarized ultrashort and ultrafast optical pulse with gapped graphene monolayer. A finite conduction band population and corresponding electric currents are generated during the pulse. In gapped graphene, inversion symmetry is broken, and while one axis, is still the axis of symmetry (y-axis), the other axis (x-axis) is no longer so, which results in generation of non-trivial currents. When the incident pulse is polarized along x-axis, both the longitudinal and transverse currents are generated. Our results show that both currents strongly depend on the bandgap. The generated electric currents transfer electrical charge and make the gapped graphene electrically polarized. The transferred charge in longitudinal direction has monotonic dependence on the field amplitude and weak dependence on the bandgap, while in transverse direction, the transferred charge shows non-monotonic dependence on the field amplitude. |
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H71.00012: Optical absorption spectrum for $\alpha-\mc{T}_3$ materials interacting with light. Dipendra Dahal, Godfrey Gumbs, Andrii Iurov, Danhong Huang We have investigated the optical absorption properties of $\alpha-\mc{T}_3$ materials, interacting with linearly and circularly polarized irradiation. The peaks in the optical absorption spectra and the plasmon modes show strong dependance on the hopping parameter $\alpha$ and a relatively moderate dependence on the strength of light-matter interaction, as well as on the polarization of the incoming off-resonance dressing field. |
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H71.00013: Temperature dependence of van Hove singularity excitons in atom thick semiconductors Garrett Benson, Viviane Zurdo Costa, Neal Border, Shirin Jamali, Kentaro Yumigeta, Mark Blei, Sefaattin Tongay, Andrew Ichimura, Akm Shah Newaz Atomically thin semiconducting transition metal dichalcogenides (TMDs) are emerging as a new platform for exploring two-dimensional exciton physics. These excitons play a crucial role in determining the light-matter interactions of a semiconducting material, such as absorption, photoluminescence, and electroluminescence. In addition to direct-band gap transition excitons (known as A- and B- excitons), there also exists a pair of van Hove singularity (vHS) assisted excitonic transitions, known as the C- and D- excitons. Currently it is not known how these vHS excitons modify at different temperature. To bridge the knowledge gap, we probed the temperature dependence of both direct-band gap and vHS excitons via photocurrent spectroscopy. We observed that all the excitonic peaks shift to lower energy as the temperature decreases. Moreover, we observed that the rate of shift for vHS excitons differs significantly from the rate of shift for the direct-band gap excitons. This study advances our understanding of the intrinsic properties of excitons in 2D TMDs. |
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H71.00014: Steering valley-polarized emission of monolayer MoS2 sandwiched in plasmonic antennas te wen, Hu Aiqin, Yang Chen, Cheng-wei Qiu, Qihuang Gong, Guowei Lv Monolayer transition metal dichalcogenides (TMDCs) have intrinsic spin-valley degrees of freedom, making it appealing to exploit valleytronic and optoelectronic applications at the nanoscale. Here, we demonstrate that a chiral plasmonic antenna consisting of two stacked gold nanorods (GNRs) can modulate strongly valley-polarized photoluminescence (PL) of monolayer MoS2 in a broad spectral range at room temperature. The valley-polarized PL of the MoS2 with the antenna can reach up to ~48% accompanied with more than three orders of magnitude enhancement of PL intensity. Also, the K and K’ valleys under opposite circularly polarized light excitation exhibit different emission intensities and directivities in the far-field, which can be attributed to the valley-dependent exciton modulation by the chiral antenna in both excitation and emission processes. The distinct features of the ultra-compact hybrid suggest potential applications for valleytronic and photonic devices, chiral quantum optics, and high-sensitive detection. |
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H71.00015: Electron transport through pair of Graphene-Superconductor junctions Shahrukh Salim, Rahul Suresh Marathe, Sankalpa Ghosh Electron transport across Graphene-Superconductor (GS) junctions have recently attracted a lot of attention [1] after it was pointed out that the Andreev processes in such junction holds distinct features as compared to Andreev processes in Normal metal-Superconductor junction because of the ultra relativistic dispersion of the charge carriers in Graphene. In this work we analyze transport properties through a pair of such junctions that can be either GSG or SGS formdue to Andreev and normal processes. In one part of the work we compare such transport with certain optical phenomena such as Goos-Hanchen shift [2] and discuss its experimentally verifiable features. We also investigate the formation of the Andreev Bound States(ABS) in hetero-junctions like SGS, and explore its connection with the transport properties; Josephson current. |
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H71.00016: Strain Imaging of Laterally-Stitched Monolayers by Nonlinear Optical Microscopy Chun An Chen, Ying-Yu Lai, Kuan-Chang Chiu, Chen Po-Han, Yi-Hsien Lee, Yu-Ting Lin, Yi-Cheng Chiang, I-Tung Chen Strain configuration is significant to crystal structure and performance of monolayer two-dimensional lattice. Heterojunction of various monolayer transition metal dichalcogenides (TMD) is emergent route to induce unique symmetry and strain configurations. Here, we realize the synthesis of diverse in-plane artificial lattice by lateral stitching of different monolayer TMD using sequential CVD growth. Highly oriented strain patterns are observed and studied by second harmonic generation imaging of the TMD multijunctions. Strain pattern with lateral and vertical heterostructures are studied using angle resolved second harmonic generation, which is practical to corelate unique properties by direct probing symmetry and strain cofiguration of monolayer TMDs. |
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H71.00017: Synthesis and enhanced magnetoresistance of WTe2 single crystals Yu-Ting Lin, Chun-An Chen, Chen Po-Han, I-Tung Chen, Yi-Cheng Chiang, Yi-Hsien Lee Tungsten ditelluride (WTe2) is one of the low symmetry two-dimensional materials and exhibits extremely large magnetoresistance (XMR) below 10K. Understanding of novel properties in the materials is highlighted to induce unique properties at elevated temperature. Study of the temperature dependent MR is essential for real applications and deep insights. Most reported studies on fundamental issues are mainly achieved in exfoliated WTe2 (for reduced disorders) which is encapsulated with h-BN layers (for ideal interfaces). Here, we demonstrate synthesis and enhanced performances of the synthesized WTe2 single crystals. Tunable thickness and high crystallinity of the WTe2 are achieved using promoter-assisted CVD. A large MR of the CVD-grown WTe2 is experimentally realized. |
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H71.00018: Carbonaceous magnetic nanocomposites Dereje Seifu, Shashi P Karna, haiping Hong Ferromagnetic nanoparticles when in proximity to low-dimension carbonaceous structures, such as 1D carbon nanotubes and 2D graphene, induce ferromagnetism in the latter through spin-orbit coupling and exchange interaction. Taking advantage of these interaction, we have created carbonaceous magnetic nanocomposites using carbon nanotubes and multilayer graphene that exhibit enhanced magnetic properties compared to the pristine nanoparticles [1-3]. The Magnetic nanoparticles studied included Fe, Fe2O3, Fe3O4, Co3O4, and CoFe2O4 on both carbon nanotubes and multilayered graphene. Structural and magnetic studies showed that magnetic enhancement occurred by proximity effect. |
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H71.00019: Nonlinear Electrical and Linear Optical Properties of Layered Graphene Oxide Dejan Maksimovski, N. G. Hallfors, Abdel Isakovic We measured a significant, two orders of magnitude decrease in the resistance of layered (5 - 100 nm) reduced graphene oxide. The resistance drops as the number of layers increases, lending a notion to the influence of out-of-plane transport being modulated by modifications to the changes in electronic structure, as additional layers are added. These changes are observed for line and area resistance, as well, indicating that geometry doesn’t play major role. In parallel with this result, we report spectroscopic study (Raman, FTIR) on the same samples, where the ratio of spectral D (1350 cm-1) and G (1580 cm-1) features shows unusual dependence on the thickness (the number of layers of graphene oxide), in that it mimics the dependence of the resistance on thickness. Detailed spectroscopic study of various bonds (some sp2 related, some not) shows a number of features that are potentially relevant for explanation of observed resistance behavior. The role of carbon vacancies is also studied, showing that the bonding of molecules external to graphene oxide becomes modified in the presence of vacancies. AFM and electron micoscopy studies complement these findings and show how layered graphene oxide large area, nanoscale thickness scale structures evolve with controlled defects. |
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H71.00020: Towards an electrically driven single photon source made from a carbon nanotube Dublin Nichols, Duy Nguyen, Ethan Minot On-demand single photon sources have potential applications in quantum cryptography, quantum computing, and metrology. In particular, there is a need for devices that can be integrated into an on-chip network and can produce indistinguishable photons on-demand. Such devices would enable practical designs for all-optical quantum computers. We aim to create electrically driven single photon sources using individual semiconducting carbon nanotubes with sp3 defects. Novel aspects of our device design include integration with van der Waals heterostructures, and the use of electrostatic gating to form p-n junctions. I will show why this is a promising platform, and discuss our progress towards fabricating a working prototype. |
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H71.00021: Transport in armchair graphene nanoribbons and in ordinary waveguides Muhammad Zubair, Mousa Bahrami, Panagiotis Vasilopoulos We study dc and ac transport along armchair graphene nanoribbons using the k.p spectrum and eigenfunctions and general linear-response expressions for the conductivities. Then, we contrast the results with those for transport along ordinary waveguides. In all cases, we assess the influence of elastic scattering by impurities, describe it quantitatively with a Drude-type contribution to the current previously not reported, and evaluate the corresponding relaxation time for long- and short-range impurity potentials. We show that this contribution dominates the response at very low frequencies. In both cases, the conductivities increase with the electron density and show cusps when new subbands start being occupied. As functions of the frequency, the conductivities in armchair graphene nanoribbons exhibit a much richer peak structure than in ordinary waveguides: in the former, intraband and interband transitions are allowed, whereas in the latter, only the intraband ones occur. This difference can be traced to that between the corresponding spectra and eigenfunctions. |
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H71.00022: Electronic Structure Study of Halogen and Gold Halide Doped Carbon Nanotubes Md Latifur Rahman, Md Hasibul Amin, Ahmed Zubair Achieving high electrical conductivity of carbon nanotubes (CNTs) through doping will facilitate its application in power transmission cable and nanoelectronic interconnects. Here, we report extremely efficient p-doping of CNT using halogen and gold halide molecules. Using ab initio theoretical calculations based on density functional theory, we investigated the effect of dopants, such as I2 and AuCl3, on the electronic band structure of semiconducting and metallic CNTs. We found that both I2 and AuCl3 introduces states between the first Van Hove singularities of conduction and valance bands. I2 was reported being an efficient dopant for CNTs. From our calculations, we confirm that large Fermi level shift occurs for both I2 and AuCl3 doping. Though the Fermi shift is much larger for AuCl3 doping. Moreover, transmission function calculations reveal that a few fold increase in available quantum channels exists for AuCl3 doping compared to I2 doping. Therefore, gold halide such as AuCl3 can be a perfect candidate as a dopant molecule of CNTs to produce conductors with ultra-high conductivities. |
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H71.00023: Investigating single-walled carbon nanotube films for LEDs and lasers Mark Steger, Bryon Larson, Kira Thurman, Andrew Ferguson, Jeffrey L Blackburn Carbon nanotubes (CNT) offer interesting optoelectronic properties including engineered conductivity and tunable infrared emission. CNTs have been extensively studied as carrier transport layers for OLEDs or as single-nanotube LEDs. Here, we investigate LED and laser architectures using CNT films as a bulk active emitter layer tunable in the near IR. We investigate the intrinsic stability of the emitter layer and optimize device structure. |
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H71.00024: Phase segregation and superconductivity in Cu doped Ni2-xCuxNbSn Heusler alloys Brandon Reese, Mahmud Khan Heusler alloys exhibit numerous exotic properties including superconductivity that can be systematically controlled via manipulation of their stoichiometry and elemental doping. It has been reported that partial substitution of Ni by Cu in Ni2-xCuxZrGa results in a systematic reduction of TC.1 Considering this observation it is interesting to explore the effect of Cu doping on the superconducting properties of other Heusler alloys. Therefore, we have performed an experimental study on the superconducting properties of partially Cu doped Ni2-xCuxNbSn materials. Ni2NbSn has 29 valence electrons per formula unit and 7.25 valence electrons per atom. The material exhibits a superconducting phase transition at TC = 3.4 K. A series of Ni2-xCuxNbSn materials were synthesized by arc-melting and annealing techniques. All materials were characterized by x-ray diffraction, dc magnetization, and transport measurements. Interestingly, a Cu concentration of 2.5% resulted in phase segregation of the system. Two superconducting transitions were observed in all compounds at temperatures near TC1 = 17.8 K, and TC2 = 3.4 K. Magnetization data has confirmed type-II superconductivity for each sample at both TC1 and TC2. |
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H71.00025: Gapless spin liquid state and quantum phase diagram in the spin-1/2 J1-J2 square Heisenberg model Wen-Yuan Liu, Shoushu Gong, Zhengcheng Gu The spin-1/2 J1-J2 square Heisenberg model is one of the most interesting and also challenging quantum spin models, due to the strongly frustrated interactions. It is of the primary candidate models to study quantum spin liquid (QSL). Despite intensively studied in the past 30 years, the nature of the intermediate nonmagnetic phase is still under great debates. Especially, whether the intermediate phase is a QSL is currently a matter of great concern to the community. A recent DMRG calculation suggests that the intermediate region is a valence bond state. However, the DMRG method is essentially a one-dimensional method. Recently, we developed an effiicent and accurate finite projected entangled pair states (PEPS) method, which can deal with a very large system in high precision. With this state-of-the-art tensor network based method, we find it is a spin liquid phase for a large region of the nonmagnetic phase, and spin correlations of the spin liquid decay in a power law form, indicating it is gapless. Methodologically, we give the first solid PEPS calculation beyond DMRG. By comparing with DMRG in details, we provide a direct numerical evidence to explicitly demonstrate the conceptual advantage of PEPS over DMRG for large 2D systems. |
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H71.00026: Thermodynamic properties of a spin-1/2 Heisenberg model on the triangular lattice Kazuhiro Seki, Seiji Yunoki By using the numerically exact diagonalization technique and a block-extended version of the finite-temperature Lanczos method, we study thermodynamic properties, such as entropy, specific heat, and uniform susceptibility, of a spin-1/2 Heisenberg model on the triangular lattice with the nearest-neighbor exchange interaction J and the four-spin exchange interaction Jc. Our calculations on small clusters containing up to 36 spins have found that, differently from the pure triangular-lattice (Jc=0) case, the temperature dependence of the specific heat exhibits a pronounced double-peak structure for finite and moderate Jc/J. |
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H71.00027: Monte Carlo Study of Three-dimensional Flat-Band Ferromagnetism in a Diamond Lattice Junjia Zhang, Eric J Bobrow, Yi Li We study the p-orbital bands in the orbital-active diamond lattice. This system features doubly-degenerate flat bands at each momentum in the Brillouin zone as well as dispersive bands exhibiting nodal-line semimetal behavior. Due to the suppression of kinetic energy, strong correlation effects lead to ferromagnetism in the flat bands, which can be mapped to a modified percolation problem. We investigate the transition between the paramagnetic and ferromagnetic phases in the flat bands via Monte Carlo simulation. |
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H71.00028: A highly sensitive TES spectrometer for resonant elastic/inelastic X-ray scattering study of quantum materials Sang Jun Lee, Sangjun Lee, Young-Il Joe, Hai Huang, William B Doriese, Jason Knight, Donghui Lu, Joel N Ullom, Paul Szypryt, Daniel Swetz, Peter Abbamonte, Jun-Sik Lee Resonant inelastic X-ray scattering (RIXS) as well as resonant elastic X-ray scattering (REXS) have been appreciated as compelling techniques in research of quantum materials. It is because the techniques deliver element-, site-, and valence-specific information through a resonance-enhanced photon-in/photon-out process. Conventionally, grating-based spectrometers have been used to measure the scattered photons in RIXS/REXS in the soft X-ray regime. However, we often experience a lack of sensitivity when a weak signal needs to be detected. Here, we introduce a novel method to overcome such difficulty using transition-edge sensors (TESs). A spectrometer built upon an array of TESs has detection efficiency that is orders of magnitude larger than a conventional grating spectrometer and has shown a spectral coverage broader than 1 keV and a moderate energy resolution of 1.5 eV (FWHM) at 500 eV. A TES spectrometer was recently integrated with the soft X-ray scattering setup at beamline 13-3 of the Stanford Synchrotron Radiation Lightsource (SSRL) and was successfully commissioned. In this poster, we will present new results taken with this new RIXS/REXS + TES approach. We believe that this approach can bring impacts to a wide range of quantum materials studies. |
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H71.00029: WITHDRAWN ABSTRACT
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H71.00030: Evidence for effects of nitrogen exposure on the Bi2Se3 density of states Michael Gottschalk, Mal-Soon Lee, Eric Goodwin, Thomas Chasapis, Mercouri Kanatzidis, S D Mahanti, Stuart Tessmer
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H71.00031: Measurement of fractional charge at disclination defects in higher-order topological crystalline insulators Christopher Peterson, Tianhe Li, Taylor L Hughes, Gaurav Bahl Topological crystalline insulators (TCIs) are known to host quantized fractional charge at boundaries and defects, which is topologically protected by bulk crystalline symmetries. Recently, this bulk-boundary correspondence was extended by the discovery of higher-order TCIs, which may host quantized fractional charge at a boundary of their boundary. Here, we use arrays of microwave resonators to experimentally study higher-order TCIs on lattices with disclination defects. Introducing a disclination defect to a finite lattice is equivalent to inserting or removing one or more sectors, changing the total number of corners and consequently introducing an overall fractional charge. Since the total charge in a lattice must remain an integer, the disclination core is expected to also host fractional charge to compensate. We experimentally measure C4-symmetric higher-order TCIs on square lattices having disclinations with positive and negative Frank angles, which respectively have 5 and 3 corners. We find that, in both cases, the disclination core does indeed host fractional charge, such that the total charge of the lattice is an integer. Furthermore, we show that there are gapless bound states associated with the defect. |
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H71.00032: Topological surface states in strained Cd3As2 thin films Pablo Villar Arribi, Timo Schumann, Susanne Stemmer, Anton Burkov, Olle Heinonen Cd3As2 is a Dirac semi-metal with two Dirac nodes near the Γ point in the first Brillouin zone aligned along the crystallographic c-axis. The structure of Cd3As2 is rather complicated with a large unit cell and it is typically grown along the (112) direction, which does result in a projection of the Fermi arc states on the (112) surface. The Dirac points are protected by inversion and C4 symmetry about the tetragonal c-axis. In recent experiments, the inversion symmetry can be broken in thin films, and the C4 symmetry can be broken by a bi-axial strain perpendicular to the c-axis [1]. This brings up the question of what happens to the Fermi arc states in the ultra-thin film limit and in the presence of broken symmetries. We are using a simple description of the low energy physics to examine the behavior of the Fermi arc states. As an example, when inversion symmetry is broken, so is the symmetry of the Fermi arc states near the Dirac points, and the two-fold degeneracy of the Dirac cones is lifted. |
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H71.00033: Chiral Anomaly and Temperature Effects in Tilted Doped Weyl Semi-metals: Dichroism And Dynamic Hall Angle Ashutosh Singh, Jules P Carbotte We calculate the absorptive part of the dynamic conductivity for both right and left handed circular polarized light in the Kubo formalism. Due to finite contribution from the imaginary part of Hall conductivity, we observe dichroism in certain frequency regime. Including the effect of chiral pumping creates difference in chemical potential in the positive and negative chirality nodes, which leads to additional regions of frequencies where dichroism remains finite. We have also considered the case of a non-centrosymmetric Weyl semi-metal in which the two nodes are displaced in energy by an amount ±Q0. This also modifies the dichroism in a similar fashion. Further, with increase in temperature (T), the boundaries of the regions of finite dichroism become smeared out in energy and extend beyond their original range for T = 0 and at the same time the dichroism is reduced. When T is increased to be of the order of the chemical potential associated with the doping, the dichroism vanishes. We have also extended the work to include the frequency variation of dynamic Hall angle for both zero and finite temperature cases. |
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H71.00034: Ultrafast optical current in Weyl semimetals Fatemeh Nematollahi, Vadym Apalkov, Mark I Stockman We study theoretically the nonlinear response of Weyl semimetals to an ultrashort optical pulse . Such strong electric field induces a finite conduction band population near the Weyl points in the reciprocal space. Also, the optical pulse causes current in the system both during and after the pulse. |
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H71.00035: Sign Change in the Anomalous Hall Effect and Strong Transport Effects in a 2D Massive Dirac Metal Due to Spin-Charge Correlated Disorder Aydin Keser, Roberto Raimondi, Dimitrie Culcer The anomalous Hall effect (AHE) is highly sensitive to disorder in the metallic phase. Here we show that statistical correlations between the charge-spin disorder sectors strongly affect the conductivity and the sign or magnitude of AHE. As the correlation between the charge and gauge-mass components increases, so does the AHE, achieving its universal value, and even exceeding it, although the system is an impure metal. The AHE can change sign when the anticorrelations reverse the sign of the effective Dirac mass, a possible mechanism behind the sign change seen in recent experiments. |
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H71.00036: Strain-engineering of Topological Type-II Dirac Semimetal NiTe2 Antonio Manesco, Pedro P. Ferreira, Lucas Eduardo Corrêa, Antonio Jefferson da Silva Machado, Gabrielle Weber, Luiz T. F. Eleno The electronic, elastic and topological properties of the equilibrium and strained type-II Dirac semimetal NiTe2 were studied within the scope of density functional theory. This bulk transition metal dichalcogenide harbor a tilted symmetry-protected Dirac cone from p-orbital bands in the vicinity of the Fermi level. The projected electronic structure and group analysis suggest that single orbital-manifold band inversion can be assigned as the mechanism behind the present topologically non-trivial states. Also, several applied strain modes are shown to be an effective route to tuning this bulk electronic trends. For instance, a small uniaxial strain along z-direction is enough to approach Dirac fermions into the Fermi energy and supress another usual non-relativistic bands from the Fermi surface. Through our investigations, we propose a static-control of the electronic states by the intercalation of light-metal monovalent species into the van der Waals gap. We also present a low-energy effective model and discuss effects of external fields and low-dimensionality. |
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H71.00037: Nonlinear Anomalous Hall Effect in Type I Weyl Metals Aydin Keser, Dimitrie Culcer Within the framework of linear response, Anomalous Hall Effect (AHE) in time reversal (TR) invariant systems is prohibited, |
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H71.00038: Hybrid Dispersion Dirac semimetal and Hybrid Weyl phases in Luttinger Semimetals: A dynamical approach Sayed Ali Akbar Ghorashi We show that hybrid Dirac and Weyl semimetals can be realized in a three-dimensional Luttinger semimetal with quadratic band touching (QBT). We illustrate this using periodic kicking scheme. In particular, we focus on a momentum-dependent drivings (nonuniform driving) and demonstrate the realization of various hybrid Dirac and Weyl semimetals. We identify a unique hybrid dispersion Dirac semimetal with two nodes, where one of the nodes is linear while the other is dispersed quadraticlly. Next, we show that by tilting QBT via periodic driving and in the presence of an external magnetic field, one can realize various single/double hybrid Weyl semimetals depending on the strength of external field. Finally, we note that in principle, phases that are found in this work could also be realized by employing the appropriate electronic interactions. |
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H71.00039: WITHDRAWN ABSTRACT
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H71.00040: 3D quantum Hall effect: Theories and recent progress Fang Qin, Chunming Wang, Haizhou Lu, Xincheng Xie The quantum Hall effect is one of the most important discoveries in condensed matter physics. Usually, the quantum Hall effect happens in 2D. A 3D quantum Hall effect has been a long-sought phase of matter. Recently, the quantized Hall resistance has been observed 3D crystals of Cd3As2 and ZrTe5 and can be attributed to the Weyl orbit and charge density wave mechanisms, respectively. In this talk, we will introduce the theories and recent progress of 3D quantum Hall effect. |
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H71.00041: Point contact Andreev reflection spectroscopy on possible chiral superconductor UTe2 Seunghun Lee, Xiaohang Zhang, Sheng Ran, Richard Greene, Nicholas Butch, Johnpierre Paglione, Ichiro Takeuchi Recent findings on a heavy-fermion superconductor, UTe2 such as 1) an exceptionally large and anisotropic upper critical field, 2) a large residual Sommerfeld coefficient, 3) the reentrant superconducting phase in a high magnetic field, and 4) pressure-enhanced superconductivity, have attracted great attention as indication of spin-triplet superconductivity. Scanning tunneling microscopy/spectroscopy measurements and microwave surface impedance measurement on UTe2 have suggested presence of the chiral edge state and normal fluid at the surface as evidence for the chiral spin-triplet pairing symmetry of the superconducting order parameter in UTe2. To further investigate the superconducting order parameter, we are performing point contact Andreev reflection (PCAR) measurements on single-crystal UTe2. PtIr and Nb tips are used to form N(I)/S and S(I)/S point-contact junctions, respectively. Evolution of conductance spectra as a function of temperature, magnetic field, and tip pressure will be discussed. |
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H71.00042: A New Frontier in Superconductivity: a Study of Hybridized Gold Clusters Ajit Hira, Jose Pacheco, Matilda Fernandez, Bridget Ortiz, Tommy Cathey In this research we utilize a combination of the tools of ab initio quantum mechanics and the tools of molecular dynamics, the Hubbard Model to study clusters of the compounds AumXn ( X = atom of a different species;, 1 =< m =< 10; and 1 =< n =< 10 ). We also looked for enhanced absorption charecteristics that have sometimes been found at sub-gap frequencies when coupling is decreased. Topological superconductors are of great interest because of the active ongoing experimental efforts to study exotic physics such as Majorana zero modes. These systems have excitations with non-Abelian exchange statistics, which can be a path to quantum information processing. Our calculations reveal two of the signatures of superconductivity at temperatures close room temperature, but not all the signatures. Further calculations are planned in attempts to place our findings on a more firm footing. Such calculations are important in light of the recent reports of room-temperature superconductivity from experimentalists in India. We also discuss the possiblility of superconductivity mechanisms other the formation of cooper pairs. |
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H71.00043: Dirac State Switching in Transition Metal Diarsenides Sabin Regmi, Gyanendra Dhakal, Md Mofazzel Hosen, Wei-Chi Chiu, Bahadur Singh, Klauss Dimitri, Baokai Wang, Firoza Kabir, Christopher Sims, William Neff, Dariusz Kaczorowski, Arun Bansil, Madhab Neupane Topological semimetals exhibiting Dirac and Weyl fermions, which support low-energy quasi-particles in condensed matter physics, have been attracting intense research interest because of the exotic properties they possess like high magnetoresistance and high carrier mobilities. The transition metal diarsenides such as MoAs2 and WAs2 have been reported to feature very large magnetoresistance suggesting the possibility of topological quantum state in these materials. Here, we present the systematic electronic structure measurements of TAs2 (T = Mo, W) by using angle-resolved photoemission spectroscopy (ARPES) complemented by first-principles calculations. We observe a single Dirac surface state in MoAs2, which switches to trivial state for different cleaving surface. Interestingly, no Dirac surface state is observed in WAs2, despite its high magnetoresistance, highlighting the role of spin-orbit coupling in the electronic structure. Our study thus provides a new perspective on how cleavage plane and spin-orbit coupling drive changes in the electronic structures in low-symmetry systems. |
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H71.00044: Long-Lived Quantum Well State Excitation and Surface Photovoltage Interplay in Topological Insulator Samuel Ciocys, Alessandra Lanzara, Ryo Mori Topological insulators with Fermi levels doped into the bulk-gap exhibit strong surface band-bending and long-lived surface photovoltage (SPV) effects. Furthermore, in-situ surface doping of the topological insulators Bi2Se3 and Bi2Te3 can lead to strong Rashba-split quantum well states. In this study, we have combined bulk-doping and surface-doping to obtain both a strong surface photovoltage and spin-momentum locked quantum well states. Remarkably, Time- and angle-resolved photoemission spectroscopy reveals an additional pump-induced quantum well state that persists for 100s of picoseconds and coincides with the surface photovoltage, as well as time-dependent modifications to the quantum well states. Our work demonstrates that topological insulators are an exemplary foundation for tunable spin-textures with complex dynamics. |
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H71.00045: Kagome bands disguised in a coloring-triangle lattice Shunhong Zhang, Meng Kang, Huaqing Huang, Wei Jiang, Xiaojuan Ni, Lei Kang, Shunping Zhang, Hongxing Xu, Zheng Liu, Feng Liu The kagome bands hosting exotic quantum phases generally and understandably pertain only to a kagome lattice. This has severely hampered the research of kagome physics due to the lack of real kagome-lattice materials. Interestingly, we discover that a coloring-triangle (CT) lattice, named after color-triangle tiling, also hosts kagome bands. We demonstrate first theoretically the equivalency between the kagome and CT lattices, and then computationally in photonic (waveguide lattice) and electronic (Au overlayer on electride Ca2N surface) systems by first-principles calculations. The theory can be generalized to even distorted kagome and CT lattices to exhibit ideal kagome bands. Our findings open an avenue to explore the alluding kagome physics. |
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H71.00046: Observation of Dirac state in DySb Klauss Dimitri, Md Mofazzel Hosen, Gyanendra Dhakal, Baokai Wang, Firoza Kabir, Christopher Sims, Sabin Regmi, Eric Bauer, Filip Ronning, Arun Bansil, Madhab Neupane Extreme magnetoresistance (XMR), magnetic and structural phase transition, and possible non-trivial topological phases in the rare-earthmonopnictide family have recently invigorated intense research interest. Recent reports have experimentally revealed the presence of a Dirac-like semimetallic phases in some lighter rare earth monopnictide materials. Here we present a systematic ARPES study as well as first-principles calculations of DySb, a potential candidate for hosting a Dirac semi-metal phase. 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, Rashba-split states are observed at the (X) point of the BZ in a certain momentum direction, which is further supported by our first-principles calculations. A Dirac state is also observed at the (X) point of the BZ in the vicinity of the magnetic transition temperature. Our study opens a new direction to look for Dirac semi-metal states in other members of the rare earth monopnictide family. |
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H71.00047: Infrared absorptions in gate-tuned twisted bilayer graphene kwangnam yu, Nguyen Van Luan, Taesoo Kim, Jiwon Jeon, Jiho kim, Pilkyung Moon, Young-Hee Lee, Eunjip Choi We show that the infrared transmission spectrum of electrically gated twisted bilayer graphene (TBG) manifests dramatic changes such as the splitting of the interlinear-band absorption step, the shift of the inter-van Hove singularity transition peak, and the emergence of a very strong intravalence (intraconduction) band transition. These anomalous optical behaviors demonstrate that non-rigid band econstruction occurs by the ion-gel gating due to layer-dependent Coulomb screening that is confirmed by our band structure calculations. We discuss the implications of such effect on the superconductivity of TBG , and also on possible applications as electrooptical device. |
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H71.00048: Engineering Floquet Higher Order Topological Insulator by Periodic Driving Ganesh Paul We theoretically investigate periodically driven two dimentional semimetal in high frequency regime and demonstrate |
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H71.00049: Higher-order Topological Phases in Dynamical Optical Lattices Haiping Hu, Biao Huang, Erhai Zhao, W.Vincent Liu We propose a versatile framework to dynamically generate Floquet higher-order topological insulators by multi-step driving of topologically trivial Hamiltonians. Two analytically solvable examples are used to illustrate this procedure to yield Floquet quadrupole and octupole insulators with zero and/or $$\pi$$-corner modes protected by mirror symmetries. Furthermore, we introduce dynamical topological invariants from the full unitary return map and show its phase bands contain Weyl singularities whose topological charges form dynamical multipole moments in the Brillouin zone. Combining them with the topological index of Floquet Hamiltonian gives a pair of $$Z_2$$ invariant $$\nu_0$$ and $$\nu_{\pi}$$ which fully characterize the higher-order topology and predict the appearance of zero- and $$\pi$$-corner modes. Our work establishes a systematic route to construct and characterize Floquet higher-order topological phases. |
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H71.00050: Stable Higgs Modes in Fulde-Ferrell-Larkin-Ovchinnikov States Zhao Huang, Chin-Sen Ting, Jian-Xin Zhu, Shizeng Lin Higgs boson is an elementary particle in the Standard Model that was discovered experimentally in 2012. The Higgs boson is massive thus requiring a huge particle collider to enable its discovery. An elementary excitation, analogous to Higgs boson, can also appear in superconductors as a consequence of the U(1) symmetry breaking. Akin to its cousin in particle physics, the Higgs boson in superconductors is very massive, which renders it short lived by decaying into quasiparticle continuum. This raises a question of how to stabilize the Higgs mode in superconductors. Here we study the Higgs mode in thin-film superconductors with spatially inhomogeneous superconducting order parameter, known as the Fulde-Ferrell-Larkin-Ovchinnikov state. By deriving an effective action for the small amplitude fluctuation in the ground state manifold, we obtain the dispersion for the Higgs mode. We find that the Higgs mode becomes massless and more stable at finite momentums. |
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H71.00051: Superconductivity Suppression in Disordered Films: Interplay of Proximity to the Two- and Three-Dimensional Localization Daniil Antonenko, Mikhail Skvortsov We revisit the problem of superconductivity suppression in homogeneously disordered thin films. Andersons theorem stating that the critical temperature is insensitive to the degree of disorder is violated in the vicinity of the Anderson localization transition. For strongly disordered films, the interplay between disorder and interaction effectively suppresses the BCS coupling constant, thereby reducing the critical temperature. For strictly 2D films, superconductivity suppression is coming from large scales (similar to the 2D localization), and summation of the leading logarithms can be performed with the help of Finkelsteins renormalization group. For thicker and sufficiently dirty films, there exists an additional effect originating from small scales (similar to the 3D localization). We calculate the corresponding contribution to the shift of the critical temperature and discuss its importance in the context of experimental situation. |
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H71.00052: WITHDRAWN ABSTRACT
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H71.00053: Shape-driven conductivity in graphene Benjamin Katz, Vincent Crespi A graphene surface is presented which has a non-vanishing density of states at the Fermi level. This is driven by defects in the sheet structure: these defects are solely odd-membered rings, forced upon the system by topological constraints due to its shape, which is a series of cones and saddles. These defects sufficiently distort the electronic structure of pure graphene such that the density of states at the Fermi level is significant. The system, physically, is globally flat--there is no net gaussian curvature--and the density of states is calculated via first principles. The system further possesses multiple stable surface configurations accessible via mechanical inversion of the cones, each with different densities of states. |
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H71.00054: Electric-field screening in multilayer graphene Nikita Tepliakov, QuanSheng Wu, Oleg V. Yazyev Electronic properties of multilayer graphene are now routinely controlled using out-of-plane applied electric fields thus enabling novel electronic and optoelectronic devices. In this work, we perform first-principles calculations with explicitly applied external electric field of varying strength on a large number of multilayer graphene models including twisted configurations. We show that multilayer graphene with N > 3 layers features a highly nonlinear electric-field screening and nonsymmetric distribution of the electrostatic potential. We further develop a highly accurate parameterization of the tight-binging model for describing multilayer graphene that includes both the electric-field screening and crystal-field splitting effects. Our work is important for the design of devices based on multilayer graphene as it provides quantitative description of the electric-field screening in this system. |
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H71.00055: First Principles dielectric spectroscopy of graphene in a tera-Hz frequency region Tomoyuki Hamada, Jun Nara, Takahisa Ohno The complex dielectric function ε1+iε2 of graphene were calculated from its electronic structure by using a first principles broadband dielectric spectrometer UVSOR (Universal Virtual Spectrometer for Optoelectronic Research) [1-3]. The ε2 was calculated by considering the direct inter-band transitions of electrons of graphene between its conduction and valence bands including those between the two-hold degenerated bands at its Dirac point. Calculations showed that the ε2 of graphene is proportional to 1/ω (ω is incident photon frequency) in a low frequency region where the electron transitions in the Dirac cone occurs and that it positively diverges as w →0eV. The optical spectra of graphene in a frequency region from 1 to 30 tera (T) Hz were calculated. Calculated optical absorption coefficients showed that graphene is a weak absorber of THz electro-magnetic waves. Details of calculations and calculation results will be given in the presentation. |
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H71.00056: Stokes and anti-Stokes Raman scattering in mono- and bilayer graphene Cong Xin, Ping-Heng Tan Stokes and anti-Stokes Raman spectroscopy associated with the intervalley double resonance (DR) process in carbon materials is a unique technique to reveal the relationship between their characteristic electronic band structures and phonon dispersion. Here, we report the Stokes and anti-Stokes Raman scattering of the 2D mode in pristine graphene. The excitation energy (Eex)-dependent frequency discrepancy between anti-Stokes and Stokes components of the 2D mode (Δω(2D)) is observed, which is in good agreement with the theoretical results. Eex-dependent Δω(2D) is attributed to the nonlinear dispersion of the in-plane transverse optical (iTO) phonon branch near the K point, confirmed by the nonlinear Eex-dependent frequency of the 2D mode (ω(2D)) in the range of 1.58–3.81 eV. The wavevector-dependent phonon group velocity of the iTO phonon branch is directly derived from Δω(2D). We also report Stokes and anti-Stokes Raman scattering of the D mode in defected graphene and the 2D mode in bilayer graphene associated with intervalley DR Raman processes. |
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H71.00057: Progress in quantum transport study of magic-angle twisted bilayer/bilayer graphene Hyeon-Woo Jeong, Jinho Park, Su-Beom Song, Jonghwan Kim, Kenji Watanabe, Takashi Taniguchi, Gil-Ho Lee Magic-angle twisted bilayer/bilayer graphene (TBBG) has shown various kinds of correlated electronic phases including superconductivity, ferromagnetism, Mott insulator [1, 2]. First, we discuss our dry transfer technique for making atomically clean TBBG with so-called tear-and-stack process. In our experiment, we measured the electron-electron interaction induced Mott insulating state at half fillings. We also observed the signature of superconducting phase near Mott insulating phase, and investigated by measuring temperature dependence and magnetic field dependence of current-voltage characteristics. As twist angle uniformity is crucial to form a macroscopic superconducting phase [3], we discuss our efforts and progress in realizing more homogeneous twist angle in TBBG devices. |
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H71.00058: Hydrodynamic Transport Theory of a non-Galilean invariant Electron Liquid Anton Andreev, Songci Li, Alex Levchenko We develop a hydrodynamic transport theory of a non-Galilean invariant electron liquid in the presence of smooth inhomogeneities with emphasis on graphene. We computed the transport coefficients near charge neutrality point and showed a break down of the Wiedemann Franz law, resembling the observations in Crossno et al. Science 351, 1058, (2016). We studied magnetotransport phenomena and showed that the magnetoresistance is positive and quadratic in weak fields. Lastly, we examined magnetothermal transport phenomena and derived the Nernst and Ettingshausen coefficients. |
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H71.00059: Growth Evaluation of Wafer-based Au-catalyzed GaAs Nanowires on GaAs(111)B Substrates with Different Patterning Conditions using µ-Raman Characterization Se-Jeong Park, Jeung Hun Park We report the relation between the catalyst patterning conditions and the intensity of the 1st order Raman active modes in Au-catalyzed GaAs nanowires. Au-patterned GaAs(111)B substrates were prepared by e-beam Litho with varying patterning conditions and GaAs NWs were grown via VLS process using a solid-source MBE. To understand the effects of the preparation conditions and resulting morphologies on the optical characteristics of 1st order TO and LO phonon modes of GaAs, the NWs were characterized by µ-Raman and SEM as a function of the e-beam dose rate, inter-dot spacing, and pattern size. The Ensembles of single crystalline NWs covered with different Au-thickness showed a downshift and asymmetric broadening of the TO and LO phonon peaks relative to GaAs bulk modes. The TO and LO intensity were clearly increased as well as the relatively higher peak shift and broadening of Raman spectra from the 100 nm pattern in response to the dose rate change. We have shown that not only the identifications of the changes in GaAs LO and Arsenic anti-site peaks are good indicators to characterize the quality of as-grown GaAs NWs but Raman spectroscopy is a powerful tool for characterizing chemical, structural, and morphological information of as-grown NWs within the supporting substrate. |
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H71.00060: Enabling Novel Approach to a controlled Fabrication of Freestanding Nanomaterials using Two Direct-Writing Technologies Keith McCormack, Nick Schaper, Nick Lavrik, Ivan Kravchenko, Maria F. Pantano, Irma Kuljanishvili Owing to their unique properties, nanoscale materials, such as nanotubes, nanowires, and 2D layered nanomaterials are emerging as key building blocks of the next generation technologies. Practical implementation of such nanomaterials necessitates their successful incorporation with well-established processes for fabrication of electrical and mechanical devices, often integrated with silicon microstructures. Typically, nanomaterials are synthesized on host substrates and transferred onto the target substrates or devices. In this work, we combine mask–free “direct-write patterning” (DWP) approach for synthesis of nanomaterials at desired locations, and the direct laser writing (DLW) technique, which is based on 2-photon polymerization, to allow for the fabrication of micro-bridge structures with sub-micrometer resolution and nanolithographic patterning of catalysts for in-situ growth of nanoscale 1D or 2D materials. We will discuss our recent results on controlled preparation of 1D and 2D nanostructures with desired morphology using DWP and DLW, as well as the characterization data from Raman, AFM, and SEM measurements. Acknowledgement. A portion of this research was conducted at the ONRL Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. |
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H71.00061: Thermal Hall Effect Measurements on UPt3 Luke Pritchard-Cairns, Andrew Huxley The heavy fermion material UPt3 is arguably the best understood unconventional superconductor to date, and has been shown to possess multiple superconducting phases [1,2]. Despite this, the symmetry of the superconducting order parameter is still somewhat up for debate, with experimental evidence for both the E2u [3] and E1u [4] representations. |
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H71.00062: Muon spin rotation and relaxation in Pr1-xNdxOs4Sb12: superconductivity and magnetism in Pr-rich alloys Pei-Chun Ho, Douglas E MacLaughlin, M Brian Maple, Lei Shu, Adrian Hillier, Oscar Bernal, Tatsuya Yanagisawa, P. K Biswas, Jian Zhang, Cheng Tan, Shoji D Hishida, Taylor McCullough-Hunter The Pr-rich end of the alloy series Pr1−xNdxOs4Sb12 has been studied using muon spin rotation and relaxation. The end compound PrOs4Sb12 is an unconventional heavy-fermion superconductor, which exhibits a spontaneous magnetic field in the superconducting phase associated with broken time-reversal symmetry. No spontaneous field is observed in the Nd-doped alloys for x ≥ 0.05. The superfluid density is insensitive to Nd concentration, and no Nd3+ static magnetism is found down to the lowest temperatures of measurement. Together with the slow suppression of the superconducting transition temperature with Nd doping, these results suggest anomalously weak coupling between Nd spins and conduction-band states. [1] |
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H71.00063: Elastic properties of hidden order in URu2Si2 are reproduced by staggered nematic order Jaron Kent-Dobias, Michael Matty, Brad J Ramshaw We develop a phenomenological mean field theory of the hidden order phase in URu2Si2 as a "staggered nematic" order. Several experimental features are reproduced when the order parameter is a nematic of the B1g representation, staggered along the c-axis: the topology of the temperature–pressure phase diagram, the response of the elastic modulus (C11 – C12) / 2 above the hidden-order transition at zero pressure, and orthorhombic symmetry breaking in the high-pressure antiferromagnetic phase. In this scenario, hidden order is characterized by broken rotational symmetry that is modulated along the c-axis, the primary order of the high-pressure phase is an unmodulated nematic state, and the triple point joining those two phases with the high-temperature paramagnetic phase is a Lifshitz point. |
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H71.00064: Electron temperature modulation at the 2D electron system in the GaAs/AlGaAs under microwave photoexcitation Tharanga Nanayakkara, U. Kushan Wijewardena, Annika Kriisa, Sajith Withanage, Ramesh Mani, Christian Reichl, werner wegscheider The magnetotransport measurements have been performed on the 2D electron system at GaAs/AlGaAs heterojunctions to understand the influence of the microwave photoexcitation on the spin splitting of the Shubnikov-de Haas oscillations at low temperatures (<1 K). The purpose of the study is to examine the temperature modulation of the electrons under microwave photoexcitation by examining observable spin splitting- and variation thereof under photoexcitation- at high filling factors. In this study, a multicomponent Lifshitz-Kosevevich1 type function has been applied to describe the magnetotransport data, and relevant results will be presented here. |
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H71.00065: Translation symmetry broken groundstates near quantum hall edge at ν=2 Amartya Saha, Ganpathy Murthy Edge reconstruction for the 2D electron gas in a magnetic field at ν=2 has been studied by Dempsey, Gelfand, and Halperin[1], who found that when the confining potential is softened the two spin polarized channels spatially separate. Using the time dependent Hartree Fock (TDHF) method we found that the collective excitations of this type of groundstate becomes unstable if we decrease the edge potential's slope beyond certail limit. This analysis is similar to what Franco and Brey[2] did for the ν=1 edge. We found two groundstates, charge density wave(CDW) and spin textured edge(STE). These phases not only have lower energy but also screens the background potential better than than the earlier proposed groundstate[1]. Finally, we study the collective excitations of these phases using TDHF method. |
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H71.00066: Two- and three-electron bubbles in AlxGa1−xAs/Al0.24Ga0.76As quantum wells Xiaojun Fu, Qianhui Shi, Michael Zudov, Geoff C Gardner, John Watson, Michael Manfra We report on transport signatures of eight distinct bubble phases in the N = 3 Landau level of an AlxGa1−xAs/Al0.24Ga0.76As quantum well with x = 0.0015. These phases occur near partial filling factors ν� ≈ 0.2 (0.8) and ν� ≈ 0.3 (0.7) and have M = 2 and M = 3 electrons (holes) per bubble, respectively. We speculate that a small amount of alloy disorder in our sample helps to distinguish these broken symmetry state in low-temperature transport measurements. |
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H71.00067: Ballistic electrons splashing down in a Fermi sea of a 1-dimenssional quantum Hall liquid Ramiro Rodriguez, Francois Parmentier, Dario Ferraro, Preden Roulleau, Ulf Gennser, Antonella Cavanna, Maura Sassetti, Fabien Portier, Dominique Mailly, Patrice Roche The one-dimensional, chiral and dissipationless edge channels of the quantum Hall effect are good canditates to form the electrical analogue of optical fibers, which alllows to coherently manipulate the propagation of single electronic wave packets. However Coulomb interactions between neighboring edge channels can lead to energy relaxation. We explore this phenomenon by measuring the energy distribution function of quasiparticles emitted at well-defined energy in an edge channel at filling factor ν = 2. Our setup relies on a pair of electrostatically defined quantum dots, used as energy-resolved emitter and detector, tunnel coupled to an edge channel. We show that, on sub-micron lengths, quasiparticles undergo a strong relaxation with a survival probability dropping exponentially with their energy. Remarkably, this relaxation preserves the position and width of the quasiparticle peak in the energy distribution function. Furthermore, at intermediate lengths, we observe a marked revival of the peak at high injection energy. Our findings are qualitatively compatible with the conventionally considered theories, however new ingredients such as dissipation seem crucial in order to provide a more quantitative comparison. |
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H71.00068: Single crystal growth of Bi2212 with different Bi/Sr ratio for terahertz waves emitters Mayu Nakayama, Takanari Kashiwagi, Takayuki Imai, Syungo Nakagawa, Genki Kuwano, Yukino Ono, Tomoyuki Shizu, Youta Kaneko, Shinji Kusunose, Jeonghyuk Kim, Manabu Tsujimoto, Takashi Yamamoto, Hidetoshi Minami, Takashi Mochiku, Hironori Nakao, Hiroshi Eisaki, Shigeyuki Ishida, Yukio Hasegawa, Richard Klemm, Kazuo Kadowaki The Bi-based copper oxide high-temperature superconductor Bi2Sr2CaCu2O8+δ (Bi2212) has a nonstoichiometry composition expressed as Bi2+xSr2-xCaCu2O8+δ. We consider that the disorder of the insulating layer due to this nonstoichiometric composition (Bi/Sr) affects the CuO2 layer and consequently changes in the superconducting transition temperature and the in-plane residual resistance. The intrinsic Josephson junctions (IJJs) constructed in Bi2212 have been thought to be affected by a crystallographic disorder. For the application of Bi2212 single crystals to terahertz wave emitters (Bi2212-THz emitters) based on IJJs, we evaluated the disorder mainly from the viewpoint of crystal structure. Specifically, we prepared single crystals of Bi2212 with different Bi/Sr ratio and subsequently the oxygen was controlled by post annealing. And the physical properties of the crystals have been examined by using X-ray techniques. We also study the device characteristics of Bi2212-THz emitters made by different ratio of (Bi/Sr) and the obtained results are compared at this moment. We will discuss these characteristics in details in the meeting. |
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H71.00069: Quantum Signatures in Superconducting-to-Normal Switching Experiments on a Multigap Superconducting Junction Roberto Ramos, Steven Carabello, Joseph Lambert, Wenqing Dai, Daniel Cunnane, Qi Li, Ke Chen, Xiaoxing Xi We review the results of our tunneling spectroscopy experiments1 which demonstrated microwave resonant activation in a multi-gap superconductor. We had measured histograms of superconducting-to-normal switching events in hybrid Josephson heterojunctions (MgB2/I/Pb and MgB2/I/Sn) at sub-Kelvin temperatures. When microwaves were coupled to the junctions, we observed peaks superposed on the histograms - features consistent with microwave resonant activation. This demonstrates microwave resonant activation in a novel superconducting multigap system where one superconducting electrode is multi-gap and the other superconducting electrode is single-gap. In this system, we have observed signatures of quantum behavior such as the Lorentzian shape of the escape rate enhancement, a saturation in the width of the switching current distribution at low temperatures, and evidence of multi-photon transitions. |
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H71.00070: Nonlinear behaviour of confined superfluid helium. Emil Varga, Vaisakh Vadakkumbatt, Alexander Shook, John Davis Superfluid Helmholtz resonators provide a versatile tool for the study of both superfluid 4He and 3He under microscopic confinement. They have proven to be effective at measuring the superfluid fraction [1] and enabled detection of emergent phases under confinement in superfluid 3He [2]. We extend previous experiments into the strongly driven regime where the resonance is nonlinear. The nature of the nonlinear behaviour depends on the isotope of helium, and on the phase in superfluid 3He. |
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H71.00071: Dynamics of 3He in a quasi-1D environment using 4He-plated MCM-41: NMR Studies Chao Huan, Johnny Adams, Marc Lewkowitz, Naoto Masuhara, Donald Candela, Neil Sullivan We utilize pulsed NMR techniques to study the dynamics of 3He atoms in quasi-1D. The quasi-1D structure was formed within the nanochannels of mesoporous MCM-41 plated with a monolayer of 4He. Measurements were carried out between 0.030K < T < 3.0K, with a 3He line density of 0.1Å-1. Direct measurement of the nuclear spin magnetization as a function of temperature show the effect of degeneracy more pronounced in a quasi-1D system compared to 3D systems. Studies of the nuclear spin-lattice interaction show a characteristic peak at 2TF, while the nuclear spin-spin interaction show unusual temperature dependencies below 0.5K. |
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H71.00072: Enhancement of critical current density in a superconducting NbSe2 step junction Xin He, Yan Wen, Chenhui Zhang, Zhiping Lai, Eugene M Chudnovsky, Xixiang Zhang We investigate the transport properties of a NbSe2 nanodevice consisting of a thin region, a thick region and a step junction. We find the critical current density has similar values for both the thin and thick regions away from the junction, while the critical current density of the thin region of the junction increases to approximately 1.8 times as compared with the values obtained for the other regions. We attribute such an enhancement of critical current density to the strong vortex pinning at the surface step. |
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H71.00073: Optimizing the Lumped Element Resonator via changing the total capacitance and the coplanar waveguide distance for effective magnon-photon coupling Yuzan Xiong, Yi Li, Tomas Polakovic, Ralu Divan, john pearson, Hongwei Qu, Zhili Xiao, Wai-Kwong Kwok, Wei Zhang, Valentyn Novosad Controllable superconducting quantum circuits with strong coupling strength is a key ingredient in the study of magnon-photon coupling in hybrid magnonic systems. The circuit's impedance is a crucial factor for optimizing the magnon-photon coupling as it strongly affects the current-flow pattern. Here, we explore the low-impedance lumped element resonator which is capacitively side-coupled to the signal line of a coplanar waveguide, by altering key parameters that were characterized with a triple-axis vector magnet at 1.5 K. The resonance frequencies are found to be inversely proportional to the circuit's total capacitance. The coupling strength is mostly affected by the distance between them. We identified a critical coupling strength, which suggests an optimal quality-factor along with a minimum insertion loss. Our studies reveal an alternative route to increase the susceptibility of magnon-photon coupling. |
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H71.00074: Transfer of Electron Exergy and Thermal Energy in Magnetic Field Andrei Sergeev, Michael Reizer Electrons placed in magnetic field create magnetization currents with kinetic and magnetic energy, which is an important part of the electron exergy. Even in the presence of an external thermal field the magnetization currents are dissipationless and, therefore, they do not produce entropy. However, temperature dependence of magnetization involve the magnetization currents into thermal phenomena in rather sophisticated way, which includes transformations of bulk currents into surface currents and interaction between magnetization currents. We review and revise the transfer of electron exergy and thermal energy in magnetic field, including Poynting vector, Onsager relations, Nernst and Ettingshausen effects in superconductors. Recent experiments with single magnetic vortices directly confirm our theoretical conclusions. |
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H71.00075: Dependence of physical properties on Bi/Sr ration and oxygen content of Bi2+xSr2-xCaCu2O8+δ Syungo Nakagawa, Tomoyuki Shizu, Hironori Nakao, Takanari Kashiwagi, Mayu Nakayama, Jeonghyuk Kim, Takayuki Imai, Manabu Tsujimoto, Yukio Hasegawa, Shigeyuki Ishida, Hiroshi Eisaki, Takashi Mochiku, Kazuo Kadowaki In order to extract the fundamental physical properties of high transition temperature (high-Tc) superconductors, one needs to take account of the details of real materials which possibly affect their properties. In the case of Bi2Sr2CaCu2O8+δ (Bi2212), non-stoichiometry due to the intersubstitution between Bi and Sr atoms exists, yielding its composition Bi2+xSr2-xCaCu2O8+δ. Accordingly, the number of hole carries (nh) as well the magnitude of chemical inhomogeneity depends on x and δ (oxygen content). In order to evaluate the precise x- and δ- dependence of the physical properties, high-quality single crystals of Bi2212 with x=0.10, 0.15, and 0.20 were grown by the Travelling-Solvent Floating Zone (TSFZ) method. The δ values were systematically changed by annealing the as-grown crystals under various conditions. To evaluate nh, we performed XAFS measurements, in which the pre-peak intensity of the oxygen K-edge absorption spectra is known to a measure of nh. We have successfully established the relationship between nh and Tc of the Bi2212 system with different amount of chemical inhomogeneity (x’s). The details of these characteristics will be presented in the meeting. |
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H71.00076: In-plane ordering of O vacancies in a high-Tc cuprate superconductor with compressed Cu-O octahedrons: an automated cluster expansion study Yunhao Li, Shiqiao Du, Zhengyu Weng, Zheng Liu A recently discovered 73K cuprate superconductor Ba2CuO4-δ implies that intact CuO2 planes are not absolutely necessary in achieving high-Tc superconductivity. Featuring an exceptional Jahn-Teller distortion, wherein the CuO6 octahedrons are compressed along the c axis, O vacancies in this material prefer to reside in the CuO2 plane, which significantly modify the 2D square lattice. By combining first-principles total energy calculation with the automated structure inversion method, the effective cluster interactions of O vacancies are mapped out. Around δ=0.8, where the superconductivity was observed experimentally, we predict that the O vacancies form a long-range order, which slice the CuO2 plane into 1D chains and two-leg ladders. The latter was not known to exist in other cuprates. A Monte Carlo simulation is performed based on the effective cluster interaction model, showing that such an ordering pattern is stable up to ~900 K. Our results put forth a concrete structural basis to discuss the underlying superconducting mechanism. |
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H71.00077: Supercondctivity in PbBe Multilayer Thin Film Thomas Nott, James G Storey, Jeffery Tallon, John Kennedy It was recently proposed by X. H. Zheng et al [1], that hetero-structures of Pb and Be would exhibit high-temperature superconductivity at 36K due to Beryllium's high Debye temperature and low mass. To investigate this we have alternately grown thin films of Pb and Be in a layered structure by the use of a vacuum evaporator. Layers were approximately 10nm each for a total film thickness of <100nm. Magnetisation measurements show a transition at ~10K, slightly above the bulk Tc of Pb, which persists to fields significantly higher than the critical field of Pb. This shows promise for Pb-Be layered systems and may be further improved with thinner, higher quality layers. |
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H71.00078: Pressure effects on superconductivity and anomalous transition in triangular lattice CuIr2Te4 Hung-Duen Yang, Hung-Cheng Wu, Yi-Chieh Chung, Ting-Wel Guo, Zong-Heng Yang, D. Chandrasekhar Kakarla, Liangzi Deng, Melissa Gooch, Ching (Paul) W Chu Geometrical spin-frustrated systems play an important role in condensed matter physics. Recently, a proposed charge-density-wave (CDW) along with superconductivity (SC) in CuIr2Te4 was reported [1] through the resistivity and magnetization measurements. It motivated us to further study the competitions between CDW and SC under external hydrostatic pressure. The CuIr2Te4 was synthesized by the solid-state reaction method and characterized using X-ray diffraction (XRD) and magnetization measurements. XRD pattern confirmed the major phase of CuIr2Te4 and the anomalous transition (Ts ~ 200 K) along with SC transition below Tc ~ 3 K in zero-field-cooling cycle was observed. The preliminary results are in agreement with the previous report [1]. Under the external pressure, both transitions (Ts and Tc) exhibit a systematic change, suggesting that a significant competition between anomalous transition and SC occurs in CuIr2Te4. The nature of anomalous transition in CuIr2Te4 will be discussed. |
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H71.00079: Structure and magnetism of Fe68.8 Pd31.2 ANUPAM SINGH, Sanjay Singh, Rajeev Rawat, Dhananjai Pandey Fe-Pd based magnetic shape memory alloys show magnetic as well as structural (martensitic) transition [1]. In the martensite phase these alloys exhibit large magnetic field induced strain about ~ 3% due to which these alloys can be used as magnetic actuators [2]. We present here the results of sample preparation, compositional analysis, X-ray diffraction (XRD) measurements and magnetic measurements. The sample is prepared by arc-meting technique and composition (Fe67.4Pd32.6) was verified through Energy Dispersive Analysis of X-rays. The Rietveld refinement shows that room temperature structure is cubic with space group Fm-3m and exhibit tetragonal phase at low temperature. The martensite transition observed around temperature T~235 K, where a sharp drop in the magnetization is observed and also confirmed by low temperature XRD. A very low thermal hysteresis of the martensite phase transition makes this system important for various applications. |
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H71.00080: Tuning the electronic and magnetic properties of Heusler alloys: A theoretical and experimental investigation Daniel Wines, Fatih Ersan, Rabin Mahat, Shambhu K KC, Sudhir Regmi, UPAMA KARKI, Prahallad Padhan, Arunava Gupta, Patrick LeClair, Can Ataca Half metallic Heusler alloys have attracted recent attention because they are suitable materials for information storage and spintronics applications. This work presents a detailed experimental and theoretical study on a series of Fe3-xVxGe, Fe3-xCrxGe, Co2Fe1-xVxGe, and Co2-xVxFeGe (0 ≤ x ≤ 1) Heusler alloys. To study these alloys, we used the cluster expansion formalism, which uses density functional theory (DFT) calculated energies as a training set, and ultimately gives us the energetics of an alloyed system as a function of concentration. We employed DFT calculations at the GGA and GGA+U level to calculate the energetic stability and the structural, electronic, mechanical and magnetic properties of each alloyed system at specific alloying ratios. Experimental measurements for these materials such as stability, lattice parameter and magnetic moment are in agreement with our calculations. Our results also confirm the half metallicity of certain alloyed materials. The findings of this study not only confirm previous experimental measurements, but can aid future experimentalists and manufacturers in the synthesis of other Heusler alloys with specific desired properties. |
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H71.00081: Structure-Property Relationships in Nanocarbon-Al Composites Made by an Electrocharging Assisted Process Madeline Morales, Xiaoxiao Ge, Christopher Klingshirn, Daniel Cole, Lourdes Salamanca-Riba Carbon nanostructures are a growing area of research due to their excellent mechanical, electrical and thermal properties. Electrocharging assisted processing of a novel class of materials, termed “covetics,” presents a practical option for macroscale production of nanocarbon-metal composites. This process incorporates carbon on the order of a couple weight percent in metals where carbon solubility is in the low ppm range. Increased tensile strength and electrical conductivity have been measured in Al covetics; however, there is minimal understanding of the structure-process-property relationship and there is high variability in measured properties among trials. We have found that the activated carbon precursor is converted to sp2 graphitic carbon with increased crystallite size. XRD and XPS show no measurable formation of carbide phases. The local electromechanical behavior measured by nanoindentation and AFM gives insight into a fundamental understanding of the improved properties in covetics, and is used to improve the fabrication process for maximal increase in electrical conductivity and tensile strength. |
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H71.00082: Ab initio investigation of solid-solid interfaces Michael Woodcox, Manuel Smeu Because a material can be engineered to satisfy a particular need through alloying, there are other properties of that material that may not be fully understood, or may be ignored entirely. While these materials may standalone as an excellent solution to a particular problem, when they interact with other materials it may drastically alter their effectiveness. In this work, we have used density functional theory (DFT) and Ab Initio Molecular Dynamics (AIMD) to investigate solder-substrate interfaces. This method is being developed to provide fundamental understanding of the atomic-scale interactions occurring at the solder joints and the impact that they have on the strength and stability of the interface. Using first principles to explore these larger systems we hope to provide a level of insight into the nature of soldering, the formation of intermetallic compounds, and an enhanced resolution of forces at the interface that would help to optimize industrial needs while also exploring the limits of system sizes that can be investigated using these methods. |
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H71.00083: Magnetic and Microstructure Properties of Co-doped rapidly solidified Ni50Mn25-xCoxGa25 Heusler alloys Imaddin Al-Omari Cobalt-doped melt-spun ribbons of Ni50Mn25-xCoxGa25 were prepared to study the influence of cobalt on the magnetic properties of the NiMnGa based Heusler alloy. Bulk specimens were also prepared for a comparative study. The bulk specimens and the melt spun ribbons were annealed at 900 deg. C for 5 hours followed by quenching. Microstructural studies revealed an extensively twinned structure which is beneficial for magnetic field induced strain. The magnetization measurements showed a reduction in the moment with an increase in the cobalt content from 78.4 emu/g to 52.7 emu/g for Co (x=6) and Co (x=10), respectively. A reduction was also observed in the TC when cobalt content was increased from Co (x=6) (TC =386K) to Co (x=10) (TC =263K). |
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H71.00084: Local structure analysis of long-period stacking ordered (LPSO) structure phase-containing Mg alloys by X-ray absorption spectroscopy Maiko Nishibori, Kohei Fujino, Kakeru Ninomiya Long-period stacking (LPSO) type Mg alloy [1] has the structure modulation and concentration modulation of the atomic arrangement in long period, and is different from the hcp structure which is a pure Mg crystal structure. In LPSO-Mg alloy, kinks are formed due to the introduction of a significant difference in grain orientation in the crystal accompanying plastic deformation, which leads to material strengthening. However, the mechanism of kink formation and its strengthening has not yet been clarified. In this study, the changes in the local structure of solid solution atoms during the formation of LPSO-phase and the kink deformation were investigated by x-ray absorption spectroscopy. As a result, the central atom of L12 cluster of LPSO-phase contained in Mg alloy was identified, and the possibility of re-diffusion of solid solution atoms by kink deformation was suggested. |
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H71.00085: Characterization of Fatigue with the Field Theory of Deformation and Fracture Conor McGibboney, Sanichiro Yoshida, Naoya Fujishima, Shun Takahashi, Tomohiro Sasaki We conducted physical experiments with metal specimens undergoing fatigue loading. Using the optical interferometric technique Electronic Speckle-Pattern Interferometry (ESPI) we analyzed the temporal behavior of the displacement pattern formed while the specimen was experiencing cyclic loads. In traditional Fatigue Analysis of aircraft wings, cracks are formed due to oscillatory loads, these cracks propagate through a structure, and a failure occurs when stresses on these cracks are above a material's ultimate strength. ESPI data from our physical experiments indicates that shear instability is related to dislocation dynamics and it can be observed by unstable temporal behavior of the displacement field, leading us to a more formal physical description of fatigue. From the viewpoint of wave dynamics described by the Field theory of Deformation and Fracture we can describe the transition from deformation to fracture in solids. Deriving field equations that govern the displacement field of solids under deformation, we conducted numerical simulations based on our physical experiments. Our hypothesis is that the Field Theory of Deformation and Fracture characterizes fatigue on a fundamental theoretical level. |
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H71.00086: Non-noble metal Ni-Mo alloys with special electronic structure as a cocatalyst for alternative Pt in photocatalysis Xin Han, Lin An, Chengyi Hou, Qinghong Zhang, Hongzhi Wang Noble metals are often used as cocatalysts in photocatalysis due to their special electrical properties. However, the high cost of noble metals severely limits the development and application of photocatalytic technology. Therefore, the development of non-noble metal cocatalysts is of great significance in the field of photocatalysis. In this work, noble-metal-free Ni-Mo alloys with different Ni/Mo ratios were developed and used as cocatalyst to replace the noble metal Pt using g-C3N4 as a substrate. Experimental results show that the optimal Ni4Mo6/g-C3N4 photocatalyst has a photocatalytic H2 production rate of up to 1785 μmol/g/h, which is about 37 times higher than that of pure g-C3N4, and comparable to that of the Pt/g-C3N4. The improved photocatalytic performance can be attributed to the presence of Ni-Mo alloys with special electronic structure, which effectively promotes the separation of photogenerated e-/h+ pairs. |
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H71.00087: Non-saturating, Sub-Liner Magnetoresistance in bulk Ge2Sb2Te5 Ming Yin, Brandon Lacey, Lei Wang, Timir Datta Phase Change materials (PCM) rapidly and reversibly switch or transform between amorphous and crystalline states. This microscopic repositioning of the system in the lattice level may give rise to large macroscopic differences in physical properties; these changes in technologically important electrical, thermal and optical parameters were discovered in 1960’s. Ambient temperature operable PCM’s are utilized in electronic flash memory drives and in optical data storage devices. Previously we have reported on a well-known PCM alloy Ge2Sb2Te5; where, based on Noritheim-Gorter like scaling between Seebeck coefficient (S) and electrical conductivity (s) we have argued the existence of two distinct types of scattering. Here we report the high magnetic field magnetoresistance in poly-crystalline specimens Ge2Sb2Te5, especially in the low temperature regime. We observe a relatively strong increase in the ohmic resistance in response to the applied magnetic field, about 150% increase between 0 - 18 T. The transport data can be precisely described by empirical functions, however, the behavior does not follow the well-known Kholer’s rule. Overall, the field dependence is sub-linear but does not quite saturates up to 18 T even in the sub-kelvin range. |
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H71.00088: Charge transport properties of ZnO, MgO, and CdO alloys Nick Boecker, Mack Adrian Dela Cruz, Gary Pennington Monte Carlo based simulations of charge transport are used to investigate how important electrical properties of doped monoxide metals can be manipulated through alloying. Results include the effects of phonon, impurity, and alloy scattering on the carrier mobility in alloys of ZnO, MgO, and CdO. The electronic structure of the alloys is determined using the virtual crystal approximation and the non-local empirical pseudopotential method, which agrees well with electronic experimental data of these materials. Results have potential applications in optoelectronic devices. |
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H71.00089: Temperature dependence of the anomalous Nernst effect in a Ni-Mn-Ga system Avirup De, Sanjay Singh, Sunil Nair Ni-Mn-Ga alloys, well-known for showing large magnetic shape memory effect, undergoes various phase transitions upon cooling, sensitive to their compositional variations. In this work, we report a detail investigation of the off-stoichiometric N i1.95Mn1.05Ga through various magnetic, electronic, and thermal characterizations. Of particular, anomalous Nernst effect (ANE) studies are presented for the first time in these class of material, revealing that the ANE is very sensitive across the pre-martensitic transition in comparison to other transport measurements. With the ANE being sensitive to changes at the Fermi surface, we infer the link of structural modulations with the modulation of the Fermi surface via its nesting features. Moreover, the large ANE-signal at room temperature and the significant drop across the martensitic transition could also be promising for many spintronics applications. |
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H71.00090: Effect of heat treatment on current induced mixed dynamic metal-insulator phase in needle-like VO2 single crystals. Bertina Fisher, Larisa Patlagan, George M. Reisner Sliding domains in the current induced mixed Metal-Insulator phase of VO2 single crystals are very sensitive on the crystal quality. Following measurements aimed to test this sensitivity were performed on an initially virgin needle-like crystal: |
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H71.00091: Effect of heat treatment on the current induced dynamic mixed metal-insulator phase in needle-like VO2 single crystals. Bertina Fisher, Larisa Patlagan, George M. Reisner Sliding domains in the current induced mixed metal insulator phase of VO2 single crystals are very sensitive on the crystal quality. Following measurements aimed to test this sensitivity were performed on an initially virgin needle-like crystal: |
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H71.00092: Mottness Collapse in 1T-TaS2−xSex Transition-Metal Dichalcogenide: An Interplay between Localized and Itinerant Orbitals Shuang Qiao, Xintong Li, Xianhui Chen, Jian Wu, Yayu Wang, Zheng Liu The layered transition-metal dichalcogenide 1T-TaS2 has been recently found to undergo a Mottinsulator-to-superconductor transition. By combining scanning tunneling microscopy measurements and first-principles calculations, we investigate the atomic scale electronic structure of the 1T-TaS2 Mott insulator and its evolution to the metallic state upon isovalent substitution of S with Se. We identify two distinct types of orbital textures—one localized and the other extended—and demonstrate that the interplay between them is the key factor that determines the electronic structure. In particular, we show that the continuous evolution of the charge gap visualized by scanning tunneling microscopy is due to the immersion of the localized-orbital-induced Hubbard bands into the extended-orbital-spanned Fermi sea, featuring a unique evolution from a Mott gap to a charge-transfer gap. |
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H71.00093: Evolution of the metallic state of LaNiO3 with thickness as observed with β-detected NMR Victoria Karner, Aris Chatzichristos, David L Cortie, Derek Fujimoto, Robert F Kiefl, Philip C. P. Levy, Ryan M. L. McFadden, Gerald Morris, Matt Pearson, Monika K Stachura, Georg Christiani, Friederike Wrobel, Bernhard Keimer, Eva Benckiser, Alexander Boris, W Andrew MacFarlane A unique set of electronic and structural conditions allow for high-Tc superconductivity in the cuprates. |
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H71.00094: Polariton Optical Transistor based on a MoSe2-WS2 Heterogenous Bilayer embedded in an Optical Microcavity at Room Temperature Patrick Serafin, German Kolmakov Exciton polaritons in an optical microcavity were shown to be a platform for the design of working elements for optical transfer and processing circuits such as optical transistors and switches. In this report, we considered a three-way superposition of cavity photons, direct excitons and indirect excitons in a bilayer semiconducting system; that is, exciton dipolaritons. Using the forced diffusion equation, we studied the room-temperature dynamics of dipolaritons in a transition-metal dichalcogenide (TMD) heterogeneous bilayer embedded in an optical microcavity. Specifically, we considered a MoSe2-WS2 heterostructure, which encompasses Y and Ψ-shaped channels guiding the dipolariton propagation. We demonstrated that optical signals propagating in the channels can be effectively redistributed between the branches of the channels by applying the driving voltage ~2V/mm to one of the TMD layers. Our findings open the route to the design of an efficient room temperature polariton based optical transistor. |
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H71.00095: WITHDRAWN ABSTRACT
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H71.00096: Polariton Formation and Propagation in an Optical Microcavity with Embedded Transition Metal Dichalcogenide with Disorder Shaina E Raklyar, Yamuna Paudel, Yuri Lvov, David Wayne Snoke, German Kolmakov Transition-metal dichalcogenides (TMD) provide a platform for optoelectronic applications at room temperatures due to strong light-matter interactions and exciton stability. By considering the coupled dynamics of cavity photons and TMD excitons, we numerically studied exciton-polariton formation and propagation in an optical microcavity with an embedded TMD layer. Specifically, we studied the case where the TMD excitons are affected by a short-scale (10-100 nm) random potential due to the interactions with the environment inside the cavity. To characterize the stability of the polaritonic states in the system, we numerically calculated the energy of eigen modes in a cavity as a function of the wave number, E(k). In our poster, we present our findings and, in particular, we discuss the crossover from the polaritonic modes formed at weak disorder to strongly broadened photonic and excitonic modes at strong disorder. We also discuss the polariton formation and propagation in a cavity where the TMD layer is non-uniform and consists of a set of separate, topologically disconnected microflakes. |
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H71.00097: Peculiar electron-phonon coupling in hBN/WS2 heterostructures Miao-Ling Lin, Yu Zhou, Hai Li, Wang Yao, Ping-Heng Tan The electron-phonon coupling (EPC) in materials is the key to the fundamental research, underlying many novel quantum behaviors. van der Waals heterostructures (vdWHs) provide new platform to reveal the intrinsic interactions between electrons and phonons. Here we report the cross-dimensional EPC between the three-dimensional (3D) layer-breathing (LB) phonons in a thick hBN/WS2 vdWH up to hundreds of layers and two-dimensional (2D) electrons of its few-layer WS2 constituent. New LB modes are resonantly enhanced in hBN/WS2 vdWHs when the excitation energy approached the C exciton energy of WS2 constituent. This cross-dimensional EPC strength is consistent with the phonon wavefunction projection between the layer-extended bulk-like LB modes in hBN/WS2 vdWHs and the LB modes strongly coupled with the C exciton in the corresponding standalone WS2 flakes, which can be further confirmed by the interlayer bond polarizability model in vdWHs. This work suggests additional possibilities to manipulate EPC in vdWHs for new quantum phenomena. |
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H71.00098: Nano-lasing from Zn-doped GaAs nanowires on Iron (Fe) substrate Gyanan Aman, ChiaWei Tu, Mykhaylo Lysevych, Hoe Tan, Chennupati Jagadish, Heidrun Schmitzer, Martin Fraenzl, Marc Cahay, Hans Peter Wagner We investigated optically pumped lasing from highly zinc-doped GaAs nanowires (NWs) on an iron (Fe) substrate at 5 K cryostat temperature. The conically shaped GaAs NWs possess an 8 nm thick Al2O3 layer around it to reduce Schottky band-banding. The NWs were optically excited with 150 fs laser pulses generated from Ti-Sapphire centered at a wavelength of 720 nm. The lasing output versus excitation power (L-L) of the lasing NWs shows the characteristic S shaped curve. Lasing NWs on Fe have a length of more than 4 µm with tip and base diameters of ~300 and~500 nm, respectively. Shorter NWs did not provide sufficient modal gain to exceed the plasmonic losses in the Fe film. The emission spectrum reveals two or three longitudinal modes, which resonate within the gain spectrum. The threshold power for NW lasers on Fe substrate were higher than for NWs on Au or glass due to significantly higher losses in the Fe film. FDTD simulations reveal that the hybrid plasmonic mode of lasing NWs on Fe has a predominantly photonic character. In a further step, we will investigate if an applied magnetic field influences the lasing behavior in GaAs NWs on Fe substrate. |
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H71.00099: Epsilon-near-zero plasmonic nanowaveguides to achieve efficient resonance energy transfer and quantum entanglement Christos Argyropoulos, Ying Li The efficient entanglement and strong resonance energy transfer between optical dipole emitters randomly distributed in a photonic system over extended time periods and long distances remain a key challenge. The main reasons are the extremely weak dipole-dipole interactions, decoherence, and dephasing between the emitters caused by radiative and nonradiative losses. We tackle this problem by proposing a practical plasmonic waveguide system to engineer both the temporal (entanglement) and spatial (resonance energy transfer and superradiance) coherent emission dynamics by an ensemble of emitters. The proposed nanoscale plasmonic waveguide system, that exhibits an effective epsilon-near-zero (ENZ) response, can simultaneously achieve the efficient inter-emitter entanglement and large enhancement of resonance energy transfer in elongated distances, long time scales, and, even more importantly, independent of the emitters’ nanoscale positions [Y. Li, A. Nemilentsau, and C. Argyropoulos, “Resonance Energy Transfer and Quantum Entanglement Mediated by Epsilon-Near-Zero and Other Plasmonic Waveguide Systems,” Nanoscale 11, 14635, 2019]. Our presented results are expected to be useful for the future quantum communication and information plasmonic-based nanodevices. |
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H71.00100: Tuning photonics structure by integrating with 2D materials Kai Hao, Robert Shreiner, Amy Butcher, Alexander A High Monolayer transition metal dichalcogenides (TMDCs) exhibit exceptional coupling to light and large electrical tunability, which make them perfect candidates for optoelectronics applications. We demonstrate the integration of TMDCs and photonic structures. Due to the strong coupling between the TMDCs and tightly confined light fields, the optical properties of the photonics structures are significantly modified. By electrically tuning the TMDCs, we can control the coupling between them and realize on demand tuning of the photonics structures. This study sheds light on future applications of TMDCs in on-chip photonics. |
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H71.00101: Critical tuning of Luttinger liquid interactions through control of ion impurities Andreas Michelsen, Manuel Valiente, Nikolaj T Zinner, Antonio Negretti Introducing ionic impurities into a Luttinger liquid (LL) of neutral atoms modifies the effective atom-atom interaction. By tuning characteristic parameters of the system, namely the short range phases of the atom-ion polarization potential and the relative density of atoms and ions, we show that the effective interaction of the LL can be tuned across a wide spectrum of values. Remarkably, the introduction of ions allows an interaction which is initially attractive to become effectively repulsive. We demonstrate this by finding the ground state of an atom-ion system using DMRG and extracting the LL parameter and the speed of sound. The LL theory models the low-energy physics of a gas of cold atoms in a one-dimensional trap, and thus these results are experimentally relevant for the recent advances in bringing different atomic species together in hybrid quantum systems. |
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H71.00102: First-principles calculation of the electronic nematicity in FeSe Xuanyu Long, Shunhong Zhang, Fa Wang, Zheng Liu We report a density functional theory calculation that produces the nonmagnetic electronic nematic state in FeSe, without explicit breaking of the tetragonal lattice symmetry. We incorporate orbital-resolved interactions by +U and hybrid functional, and precondition the initial wavefunction to find local energy minima with spontaneous symmetry breaking. The lowest-energy nematic state we find features an anti-ferro hexadecapolar charge order, instead of a simple ferro-orbital order, which is important to produce the correct Fermi surface topology in FeSe. We propose that the weak inversion symmetry breaking induced by this multipolar order can be detected by high-precision measurement of the band dispersion as well as second-harmonic generation. |
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H71.00103: WITHDRAWN ABSTRACT
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H71.00104: Bogoliubov-de Gennes analysis of superconducting gap in nanowires and nanotubes German Lopez, Chumin Wang Most quantum theories of superconductivity have been formulated in the reciprocal space by taking the advantage of translational symmetry. Such symmetry is absent in many nanostructured superconductors, whose study requires a real space approach such as the Bogoliubov-de Gennes formalism [1]. In this work, the inhomogenious superconducting gap [2,3] in nanostructures is studied by means of a simple attractive Hubbard model. The results show a unique critical temperature for each nanostructure despite the variation of its local superconducting gap and the spectral average of such gap over the chemical potential location grows when its coordination number diminishes. The latter suggests that the superconductivity in nanostructures could be enhanced by the quantum confinement of electrons, which reduces its kinetic energy and accentuates the potential one. |
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H71.00105: Effects of percolation on the superconductor-insulator transition in thin films Kristine Ung, Robert Lynn, Samuel Shapiro, Nina Markovic Thin films of superconductors are known to undergo a quantum phase transition into the insulating state as a function of disorder and magnetic field, but the nature of the transition has been debated for decades. In order to investigate the effects of percolation and rare superconducting regions on the superconductor-insulator transition in thin films, we have fabricated a series of nanostructured films with controlled vicinity to the percolation threshold. We will show how the measurements of resistance as a function of temperature and magnetic field correlate to the physical texture of the films. |
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H71.00106: Domains, Domain Walls, and Phase Slips in the Nearly-Commensurate Charge Density Wave Phase of 1T-TaS2 Boning Yu, Manoj k Singh, Bishnu Sharma, Michael Boyer The nearly-commensurate charge density wave (CDW) state of 1T-TaS2 consists of hexagonally ordered domains. Within these domains, the CDW state is commensurate with the lattice. However, there are domain walls which include phase slips in the CDW state between neighboring domains. Here we combine our scanning tunneling microscopy (STM) data of the nearly-commensurate CDW state with computer simulations to study, at the atomic-scale, domains, domain ordering, and phase slips at domain walls in 1T-TaS2. In particular, we examine how these features manifest themselves in Fourier transforms of STM topographic images. |
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H71.00107: The low frequency surface slasmons in multicoaxial NIM cables: Zero magnetic field Manvir Kushwaha, Bahram Djafari-Rouhani Employing an elegant response function theory1-3, which does not require matching of the messy boundary conditions, |
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H71.00108: Harnessing the magneto-optics in quantum wires for observing the quantum pinch effect Manvir Kushwaha Here, we report on a two-component, |
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H71.00109: Nanoporous Metal Foams as Efficient Particulate Filters James Malloy, Kai Liu Nanostructured metal foams offer exciting potential for applications in diverse fields such as catalysts, electronics, heat exchange, structural materials, and filtration due to their extremely high surface area to volume ratios. We have achieved a variety of metallic foams using electrochemical methods, with strong mechanical stability and tunable porosity and density (0.1%-30% of bulk density) [1]. Uniaxial compression tests reveal significantly varying structural strengths depending on the relative density. Additional physical characteristics and applications have been explored. We have also investigated using such foams as efficient filtration membranes for micron and sub-micron sized particles. Over 99% of airborne micron sized particles are found to be filtered after passing through just 1 mm of metallic foam. The foams are also found to be effective for filtering out deep submicron particles. The pressure drops across the foams are found to vary depending on the bulk density of the foam; with the lower density foams being comparable to commercial HEPA filters. |
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H71.00110: Sub-5 nm patterning via self-assembly and template-assisted assembly of colloidal nanocrystals Austin Keller, Cherie Kagan, Christopher B Murray, Di An We explore using colloidal lithography and conventional fabrication tools for patterning substrates at and below the 5 nm scale. Our processing pathway combines bottom-up methods using inorganic nanocrystal (NC) synthesis and self-assembly techniques with top-down nanofabrication techniques. A pattern is established by the size, shape, and arrangement of discrete NC building-blocks, and the density is determined by the interparticle spacing of each element. The collective arrangement of each element sets the ensemble pattern, where each NC serves as a discrete hard etch mask. We explore self-assembly at a liquid-air interface and topographic template-assisted capillary assembly methods to establish the NC patterns. This pattern is transferred to the underlying substrate using inductively couple plasma reactive ion etching, and a selective chemical wet etch is used to remove any remaining mask material after pattern transfer. The NC systems explored are Fe3O4 spheres, TiO2 rods, and GdF3 rhombic plates with CF4 and Cl2 plasma etch chemistries. The goal of our pathway is to implement innovative processing methods into already well-established fabrication methods and technology, while maintaining process simplification and enabling wider access to patterning at the deep nanoscale. |
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H71.00111: Skyrmions on a sphere shell Delaram Nematollahi, Kieran Mullen Skyrmions, as small electronic spin-structures, provide a window into strongly interacting many electron systems. The existence of these spin-textures has been studied in quantum Hall (QH) ferromagnets, in which the kinetic energy of the electrons is quenched by the strong external magnetic field. The large angular momentum (l) single particle states on the surface of a sphere are similarly degenerate in energy as a function of their z component (m) for fixed (l). This makes electrons on a sphere an interesting system for studying spin textures. Using Hartree-Fock theory, we initially force a skyrmionic texture on the system by applying a small “scaffolding” field that couples to the spins to produce a texture and investigate the stability of the spin-structure as the field goes to zero. We study the dependence of the skyrmion stability on the number of electrons, the choice of interactive potential, and material parameters. |
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H71.00112: Metallic density of states in the spin liquid RuCl3. Andreas Rydh, Ali Bangura, Kimberly Modic, Gregory Scott Boebinger, Brad J Ramshaw, Ross McDonald, Arkady Shekhter We use resonant line-width spectroscopy and SiN nanocalorimeters to measure specific heat of a small (~1μg mass) RuCl3 sample. The low-temperature limit of C/T is metallic-like, with an extrapolated Sommerfeld coefficient corresponding to a density of states of about 100 mJ/molK2, consistent with Majorana fermions of about 10meV bandwidth. We discuss the field- and angular evolution of this metallic density of states. Finally we examine thermodynamics of the AFM boundary, as well as AFM spin waves in RuCl3. |
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H71.00113: Heat Capacity Studies of Nano-Confined Argon Erin Marlowe The effect of confinement on the thermodynamic properties and phase transitions of liquids and solids in confinement has been of long-standing interest and recent interest has focused on the effects of dimensionality. Hydrogen has been of interest due to the importance of quantum effects, in particular zero-point motion, and has been studied extensively in a variety of porous media. Argon is a good model for hydrogen as it will exhibit similar behaviors, in general, to hydrogen. Furthermore, it is important to understand the behavior of noble gasses in confinement as it may be useful for understanding gasses like hydrogen. Templated porous materials, such as MCM-41, provide an attractive model system for studying the effects of confinement due to their highly uniform one-dimensional pores with variable pore size. Unfortunately, the minimum pore diameter is typically limited to a few nanometers which limits our ability to approach the one-dimensional limit. We will present measurements of the heat capacity of argon confined in MCM-41. |
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H71.00114: Effects of Metamaterial Engineering on Properties of Ultrathin Layers of NbTiN Jonathon Cartelli, Will Korzi, Anne-Marie Valente-Feliciano, Joseph Prestigiacomo, Michael Osofsky, Igor Smolyaninov, Vera N Smolyaninova Application of the metamaterial dielectric function engineering is capable of enhancing superconducting properties in type I superconductors such as aluminum and tin, leading to the tripling of the critical temperature Tc in Al-Al2O3 epsilon near zero (ENZ) core-shell metamaterial superconductors. Similar effects have been observed in hyperbolic (superconductor/dielectric) metamaterials [1]. Here, we report on the effects of metamaterial dielectric function engineering on superconducting properties of ultrathin layers of NbTiN. NbTiN/AlN multilayers with varied number of layers and layer thicknesses were fabricated. Dielectric constants of these metamaterials were measured via polarization reflectometry will be reported. Correlation of the results of the transport measurements and the hyperbolic properties of the multilayers will be discussed. |
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H71.00115: Introducing a new noncentrosymmetric superconductor: Zr3Ir Sajilesh K P, D Singh, P. K Biswas, R P Singh An intrinsic momentum dependent antisymmetric spin-orbit coupling (ASOC) in noncentrosymmetric (NCS) systems arising due to lack of inversion center in the crystal structure gives way to numerous unusual superconducting properties [1]. The Fermi surface in these systems becomes nondegenerate in the presence of spin-orbit coupling, giving a plausibility to form an admixed superconducting order parameter. This breaks the conventional notion of even parity spin-singlet and odd parity spin-triplet order parameter, leading to the high upper critical field, anisotropic superconducting gap, and time-reversal symmetry breaking [1]. We report a new NCS compound Zr3Ir, crystallizes in a tetragonal α-V3S structure. The magnetization, specific heat, and muon spin rotation confirm s-wave superconductivity, having a transition temperature Tc = 2.3 K. Muon spin relaxation confirms the preservation of time reversal symmetry in the superconducting ground state [2]. |
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H71.00116: Probing the superconducting ground state of noncentrosymmetric superconductors using muon spectroscopy: A case of Re-based compounds deepak singh, R P Singh, Adrian Hillier, P. K Biswas, Sourav Marik, Sajilesh K P Noncentrosymmetric superconductors (NCSs) with broken inversion symmetry has a direct influence on the superconducting properties of the system. In particular, NCSs with α-manganese structure has attracted much attention recently, after the discovery of time reversal symmetry breaking (TRSB) in all the members of the Re6X (X = Ti, Hf, Zr) family [1,2]. Its persistence and the independent nature of the particular transition metal, points to a key role played by Re. To test such a hypothesis, and to ascertain the possible relevance of the noncentrosymmetric structure to TRSB in Re-based NCSs, we proceeded with a twofold study. On one hand, we studied the Re6X family of compounds using muon spectroscopy, whereas, on the other hand we also studied the NbOs2 compound, which doesn’t contain Re as the primary element and adopts similar α-Mn structure with superconducting transition temperature Tc = 2.7 K [3]. The results of muon spin relaxation/rotation measurements strongly suggests that the local electronic structure of Re is crucial for understanding the TRSB superconducting state in Re6X. |
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H71.00117: Physical properties of (Mn1-xFex)Si at x=0.15 along the critical trajectory Alla E Petrova, Sergey Yu Gavrilkin, Dirk Menzel, Sergei Stishov We report results of studying the magnetization, specic heat and thermal expansion of a single |
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H71.00118: Investigation of quantum criticality in α-RuCl3 by means of dilatometry Anja Wolter, Sebastian Gass, Laura T. Corredor, Vilmos Kocsis, Lukas Janssen, Matthias Vojta, Paula J Kelley, Stephen E Nagler, David Mandrus, Bernd Buechner The quantum spin liquid candidate α-RuCl3 shows field-induced quantum criticality around μ0Hc~7-8 T, where the antiferromagnetic zigzag phase is suppressed [1,2]. Such behavior can be studied via the characteristic divergence in the temperature and field dependence of the Grüneisen parameter [3]. |
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H71.00119: Percolation and Quantum Criticality: a New Universality Class Sean Fayfar, Alex Bretaña, Wouter Montfrooij, Thomas Heitmann We present the results of computer simulations on a class of percolation systems that form a new universality class. We show the results for the critical exponents for this new class, based on simulations of two- and three-dimensional lattices consisting of half a billion sites, and discuss the ensuing modified scaling laws. |
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H71.00120: Validity of Harris criterion for two-dimensional quantum spin systems with quenched disorder Jhao-Hong Peng, Leng-Wei Huang, Deng-Ruei Tan, Fu-Jiun Jiang Inspired by the recent results regarding whether the Harris criterion is valid for quantum spin systems, we have simulated a two-dimensional spin-1/2 Heisenberg model on the square lattice with a specific kind of quenched disorder using the quantum Monte Carlo (QMC) calculations. The considered quenched disorder has a tunable parameter 0≤p≤1 which can be considered as a measure of randomness. Interestingly, when the magnitude of p increases from 0 to 0.9, at the associated quantum phase transitions the value of the correlation length exponent ν grows from a number compatible with the O(3) result 0.7112(5) to a number slightly greater than 1. In other words, by varying p, ν can reach an outcome between 0.7112(5) and 1 (or greater). Moreover, among the studied values of p, all the associated ν violate the Harris criterion except the one corresponding to p=0.9. Considering the form of the employed disorder here, the above described scenario should remain true for other randomness if it is based on the similar idea as the one used in this study. This is indeed confirmed by our preliminary results stemming from investigating another disorder distribution. |
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H71.00121: Percolation Physics in doped and stochiometric Quantum Critical Systems Alex Bretaña, Sean Fayfar, Wouter Montfrooij, Thomas Heitmann We argue that spontaneous fragmentation of the magnetic lattice in strongly correlated electron systems close to the quantum critical point accounts for most of the observed non-Fermi liquid behavior. Upon cooling, magnetic fragmentation of the Kondo lattice is caused by a distribution of Kondo temperatures, which in turn originate from small variations in interionic separations (0.05-0.1 A). This temperature-dependent fragmentation transforms the magnetic lattice to a percolation system resulting in the creation of isolated clusters which dominate the low-temperature response of quantum critical systems. We argue the validity of this new scenario for the physics near a QCP using literature data on systems where interionic distances have been modified by means of chemical doping (e.g., UCu4Au) as well as stoichiometric systems where zero-point phonons are responsible for such variations (e.g., CeRu2Si2). The percolation physics describing QCP-systems represents a new universality class (see Fayfar et al.). This new class appears to violate the Harris criterion, thereby providing a natural explanation for the lack of universality of the critical exponents observed in QCP-systems. |
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H71.00122: Many-Body Localization in Central Spin. Marcos Trivelato, Carlos Egues, John Schliemann, Joao Vitor Ignacio Costa We investigate many-body localization in a periodic one dimensional Heisenberg chain, with a central spin interacting equally with each spin in the chain. The chain is subject to a uniaxial quenched disorder field. Apart from a detailed analysis of the phase diagram, we study the time evolution of nonlocal out-ot-time-ordered correlators to diagnose the information scrambling in the dynamics of the system. |
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H71.00123: Multi-Layer Restricted Boltzmann Machine Representation of 1D Quantum Many-Body Wave Functions Huan He, Yunqin Zheng, Andrei Bernevig, German Sierra We consider representing two classes of 1D quantum wave functions of spin systems, including the AKLT and CFT correlator wave functions, in terms of multi-layer restricted Boltzmann machines. In our prescription, the AKLT wave function can be exactly represented by a 2-layer restricted Boltzmann machine with five hidden spins per visible spin. The construction can be generalized to prove that any MPS wave function on $N$ unit cells with finite bond dimension can be approximated by a 2-layer restricted Boltzmann machine with O(N) hidden spins within an error which scales linearly with $N$. The Haldane-Shastry wave function or a chiral boson CFT correlator wave function, as any Jastrow type of wave functions, can be exactly written as a 1-layer Boltzmann machine with O(N^2) hidden spins and N visible spins. Applying the cumulant expansion, we further find that the chiral boson CFT correlator wave function (with small vertex operator conformal dimension $\alpha$, i.e., $\alpha<0.1$) can be approximated, within 99.9\% accuracy up to 22 visible spins, by a 1-layer RBM with O(N) hidden spins. The cumulant expansion also suggests that the hidden spins of the restricted Boltzmann machine can be interpreted as the conformal tower of the chiral boson CFT on the cylinder. |
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H71.00124: Puzzling "bad metal" resistivity and optical conductivity of normal-state cuprates: an emergent Bose liquid perspective Long Zou, Zijian Lang, Shengtao Jiang, Wei Ku We investigate anomalous normal-state in-plane resistivity and optical conductivity of cuprates by using multi-orbital bose-liquid model. Specifically, we assume that the charge carriers in cuprate are tightly bound pre-formed pairs. We show the low-energy optical spectrum involving both intra- and inter-band excitation. While inter-band excitation explain the continuous spectrum and its contribution around the van-Hove singularities of the pre-formed pairs can reproduce the experimental observed onset near 1000cm-1, the intra-band excitation will mainly contributes to low frequency conductivity and gives rise to linear resistivity without saturation. Instead of considering about the mean free path, we demonstrate this universal bad metal behavior originate from the continuously decreasing height of low-frequency peak since its weight transfers to high energy region with temperature.Our study reveals the bosonic nature of the low-energy carriers and provides a strong support for the picture of tightly bound preformed pairs in describing the high-temperature superconductivity and other low-energy physics of the cuprates. |
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H71.00125: "Time-reversal symmetry breaking in topological superconductor Sr0.1Bi2Se3" P. Neha, K. S. Jat, Tanmoy Das, S. Patnaik We report on the detection of the TRS breaking in the topological superconductor Sr0.1Bi2Se3, probed by zero-field μSR measurements. The TRS breaking provides strong evidence for the existence of a spin-triplet pairing state. The existence of TRS breaking is also verified by longitudinal-field μSR measurements, which negates the possibility of magnetic impurities as the source of TRS breaking. The temperature-dependent superfluid density deduced from transverse-field μSR measurements yields nodeless superconductivity with low superconducting carrier density and penetration depth λ = 1622(134) nm. From the microscopic theory of unconventional pairing, we find that such a fully gapped spin-triplet pairing channel is promoted by the complex interplay between the structural hexagonal warping and higher order Dresselhaus spinorbit-coupling terms. Based on Ginzburg-Landau analysis, we delineate the mixing of singlet- to triplet-pairing symmetry as the chemical potential is tuned far above from the Dirac cone. Our observation of such spontaneous TRS breaking chiral superconductivity on a helical surface state, protected by the TRS invariant bulk topology, can open avenues for interesting research and applications. |
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H71.00126: Tight-binding Models for Two-dimensional Allotropes of Bismuth based on Wannier Functions Qile Li, Jackson Smith, Yuefeng Yin, Chutian Wang, Mykhailo V. Klymenko, Jared H. Cole, Nikhil Medhekar Recently two-dimensional allotropes of bismuth have attracted significant attention in the study of topological materials due to the strong correlation between their crystalline symmetry and electronic band topology. This connection has been studied previously by directly transferring the empirical tight-binding models of semi-metallic bulk bismuth to its two-dimensional counterparts. However, this approach fails to describe the electronic structure of two-dimensional bismuth correctly. Therefore, new physical models are required when considering the two-dimensional forms of bismuth. In this study, we have constructed tight-binding models based on the Wannier representations derived from the Bloch states in first principles calculations. We have successfully reproduced the band features for three types of two-dimensional bismuth allotropes (Bi(111), Bi(110) and bismuthene) with minimal tight-binding parameters. We have verified the accuracy of the model by calculating band representations and topological invariants. We expect these simple but accurate tight-binding models can help to examine the electronic transport in these systems more effectively in the future. |
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H71.00127: Probing black hole-like quasinormal modes in quantum Hall point contact geometries Suraj Hegde, Varsha Subramanyan, Barry Bradlyn, Smitha Vishveshwara Recently it was shown by the authors that quantum Hall systems under the influence of an external saddle potential can realize the inverted harmonic oscillator(IHO), which is of importance in its own right and in the context of black hole physics [*]. A key feature of this potential is the occurrence of the resonant states/ quasinormal modes(QNMs) that decay in time via a finite outward flux. In this talk, we explore the directions for feasible experimental realisation and detection of these states. We analyze the bounded scattering potential of the Pöschll-Teller model whose scattering matrix has a resonant pole structure comparable to the IHO. We study quantities such as the non-escape probability that could be amenable to measurement and extraction of the decay rates of QNMs. We propose time-resolved measurements in quantum Hall point contact architectures for experimentally probing these wave packet scattering phenomena. |
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H71.00128: Probing the stability of Shastry Sutherland lattice in Er2Pd2Sn and Er2Pd2In Gicela Saucedo Salas, Sahu Baidyanath, Andre Michael Strydom, Stuart Calder, Harikrishnan S Nair The group of 2:2:1 compound crystalizing in the Mo2FeB2 structure type, more commonly known as R2T2X intermetallic (R = rare earth, T = transition metal, X =main group), have been reinvestigated recently owing to the spin liquid state in the underlying Shastry-Sutherland lattice (SSL) formed by the R [1, 2]. Our motivation in investigating this compound is to explore the interplay of frustration and quantum criticality. For this study we have selected less-investigated Er2Pd2In and Er2Pd2Sn. X-ray powder diffraction studies and subsequent Rietveld refinements confirmed that the compounds were phase-pure and crystallized in the tetragonal Mo2FeB2 structure. Both the compounds obeyed Curie-Weiss law in the paramagnetic regime, as judged from magnetic susceptibility data, which indicated anti-ferromagnetism. Specific heat data on both the compounds revealed a double peak indicating complex magnetic structure and phase transitions. We will present a detailed analysis of the magnetization and specific heat on both Er2Pd2(Sn/In). This motivated our current neutron diffraction experiment to determine the magnetic structure of these SSL compounds to probe for novel magnetic phases. |
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H71.00129: Thermoelectric transport in electronic systems at low and intermediate temperatures Zahidul Islam Jitu, Woo-Ram Lee, Alexander Finkelstein, Karen Michaeli, Georg Schwiete Measurements of thermoelectric transport in correlated electron systems probe different aspects of the many-body dynamics compared to electric and thermal transport. Here, we study theoretically how electron-electron interactions influence the Seebeck coefficient (thermopower) in disordered conductors when the phonon-drag is negligible. In particular, we discuss the regime of intermediate temperatures, where inelastic electron-electron collisions and elastic scattering on impurities occur at similar rates, and the low-temperature regime, where impurities provide the dominant scattering mechanism. |
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H71.00130: Valence Transition in CeOs4Sb12 and Its T-H Phase Diagram Pei-Chun Ho, John Singleton, Marcelo Jaime, Kathrin Goetze, Matthew Pearce, Paul Goddard, Kalyan Sasmal, M Brian Maple, Tatsuya Yanagisawa The filled skutterudite compound CeOs4Sb12 displays Kondo insulating behavior accompanied by a ~1 K Spin-Density-Wave order state. Recently it has also been suggested as a potential topological insulator. In penetration depth and magnetic susceptibility measurements, we found a Fermi-surface reconstruction in CeOs4Sb12 and an unusual phase boundary in the temperature T vs magnetic field H diagram associated with the valence transition from the Ce4+ to Ce3+ state, denoted as an L and an H phase, respectively. Based on the experimental features from magnetostriction, magnetoresistance, and high T skin depth, a newly modified T-H phase boundary of the L to H phases becoming much broader than what originally thought.1,2 The cyclotron mass of the conduction electron has a significant enhancement below ~35 T. |
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H71.00131: Kondo effect in a spin-orbit coupled quantum wire under the influence of an external magnetic field Edson Vernek, George B Martins, Rok Zitko We performed a detailed study of the Kondo effect occurring in a quantum dot coupled to a nanowire with Rashba and Dresselhaus spin-orbit couplings (SOC) subjected to an external magnetic field. We report the results for local static and dynamic physical properties of the dot in the Kondo regime obtained through the Numerical Renormalization Group method. Despite the SOC-induced magnetic anisotropy of the bands, the local quantum dot properties remain isotropic in the spin space at zero external field. However, when an external magnetic field is applied to the system, clear fingerprints of the SOC-induced anisotropy are revealed through the quantum dot physical properties that become dependant on the direction of the field. We demonstrate that the quantitative evaluation of this SOC-induced anisotropy, measured by tunneling spectroscopy techniques, can be used to determine the ratio of Rashba and Dresselhaus SOC strengths in the wire. |
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H71.00132: Effect of pseudospin-1 fermions on the RKKY interaction in α-T3 lattice Godfrey Gumbs, Andrii Iurov, Danhong Huang The interaction energy for the indirect-exchange or Ruderman-Kittel-Kasuva-Yosida (RKKY) interaction between magnetic spins localized on lattice sites of the α-T3 model is calculated using linear response theory. In this model, the AB-honeycomb lattice structure is supplemented with C atoms at the centers of the hexagonal lattice. This introduces a parameter alpha for the ratio of the hopping integral from hub-to-rim and that around the rim of the hexagonal lattice. A valley and alpha-dependent retarded Green’s function matrix in momentum-energy space is generated using the (A,B,C) lattice basis forming the low-energy Hamiltonian. The corresponding coordinate space Green’s functions not only depend on which sublattice (A,B or C) the interacting spins are located but the cut-off wave vector used in the Fourier transform integral restricted to lie within the first Brillouin zone (B.Z.). |
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H71.00133: Plasmon dispersion in semimetallic pseudospin-1 α-T3-based nanoribbons Andrii Iurov, Paula Fekete, Liubov Zhemchuzhna, Dipendra Dahal, Godfrey Gumbs, Danhong Huang We have calculated the electronic states, Coulomb potential energy, dynamical polarizability and the plasmon discpersion |
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H71.00134: Suspended Nanowire Devices as Templates for Size-selected Nanocluster Networks Patrick Edwards, Marko S. Chavez, Mohamed Y. El-Naggar, Vitaly V Kresin
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H71.00135: Resonant Scattering of Light from Dielectric Nanopillars Aminatou Dabokemp, Huizhong Xu The use of plasmonic nanoparticles dispersed in a visibly transparent polymer matrix has recently emerged as a promising alternative approach to realize transparent display [1]. The localized surface plasmon resonance of these particles allows them to selectively scatter light at certain wavelengths. However, their performance is limited due to the inherent absorption in these plasmonic particles. In this study, we use finite element method to study scattering of light from titanium dioxide nanopillars. Due to the large refractive index contrast between the nanopillar and its surrounding medium, strong resonant scattering can be achieved across the entire visible spectrum by varying its dimensions. As a result of zero absorption and sharp resonances, the figure of merit of these structures for transparent display applications is found to exceed values previously reported for plasmonic nanoparticles. Furthermore, the angular distribution of light scattered from these structures can be tuned by varying their dimensions. These nanopillar structures may be used to create novel metasurfaces with applications in metalenses, see-through head-up displays, and smart glasses. |
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H71.00136: Patterned Fabrication of Dielectric Nanopillar Arrays for Single Molecule Spectroscopy Applications Patrick DeLear, Chelsea Howard, Joseph Chandler, Brian Le, Oskar Garcia, Huizhong Xu The ability to guide and confine light on a scale much smaller than the wavelength of light opens up a variety of applications in fields including information processing, nanoscale imaging and lithography, and single molecule spectroscopy. For example, our previous studies have demonstrated the efficient guiding of visible light through 50-nm-diameter zinc oxide nanowire waveguides. However, the lengths of these zinc oxide nanowires are not well controlled due to the chemical synthesis method used, prohibiting their application in devices for single molecule spectroscopy. In this study, we use nanofabrication techniques to demonstrate the fabrication of titanium oxide nanopillars with controlled diameter and length. The use of these titanium oxide nanopillar waveguides for single molecule studies with fluorescence correlation spectroscopy at micromolar concentrations is probed and its application in studying the dynamics of protein molecules on cell membranes will be explored. |
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H71.00137: The magneto-optics in quantum wires comprised of vertically stacked quantum dots: A calling for the magnetoplasmon qubits Manvir Kushwaha A deeper sense of advantages over the planar quantum dots and the foreseen applications in the single-electron |
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H71.00138: One-phonon resonant Raman scattering in a nanowire in presence of an external electric field Maricela Fernández Lozada, Ricardo Betancourt Riera, René Betancourt Riera, Raúl Riera Aroche In this work, the emission spectra for a one-phonon resonant Raman scattering process in a semiconductor nanowire of GaAs with a cylindrical symmetry in the presence of an external transversal and homogeneous electric field, as a mechanism for controlling the electron states and the selection rules due to confinement, are presented. The theoretical model considers single parabolic conduction and valence bands which are split into a sub-bands system due to confinement and electric field. We have considered Frölich type Hamiltonian for the electron-phonon interaction and only Stokes process, where the Comas-Trallero model for a free-standing wire has been used. Moreover, the electron intermediate states correspond to uncorrelated electron-hole pairs. As a result, the emission spectra corresponding to different laser energies and the selection rules for the process are discussed. The electric field produces the appearance of transitions linked to phonon oscillation modes where despite using dipole approximation in the electron-photon interaction. |
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H71.00139: Carrier dynamics in ultrathin gold nanowires: Role of Auger processes Gyan Prakash, Subhajit Kundu, Ahin Roy, N Ravishankar, Abhishek K Singh, A K Sood Carrier dynamics in metallic nanostructures is strongly influenced by their confining dimensions. Gold nanoparticles of size ∼ 2 nm lie at the boundary separating metallic and non-metallic behavior. Here, we examine the carrier dynamics in high aspect ratio ultrathin gold nanowires (Au-UNWs) of average diameter ∼2 nm using pump (3.1 eV) and coherent white-light continuum as a probe in the spectral range of 1.15 eV to 2.75 eV. We find that the transient carrier dynamics in Au-UNWs under extreme excitation regime is slower than predicted by the often used two-temperature model. Systematically probing the dynamics by varying the pump intensity from weak to strong excitation regime reveals that the mechanism of carrier relaxation through electron-phonon observed so far in larger size Au nanostructures is not sufficient in the Au-UNWs. We show that the reduced screening of e-e interaction due to spilling of conduction band and localization of core (d band) electrons at the surface promotes Auger heating. |
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H71.00140: Extending classical computational electrodynamics to quantum domain Christopher Silfies, Jiantao Kong The Finite-Difference Time-Domain (FDTD) method [1] is widely used to simulate electromagnetic response of metallic structures, where abrupt boundary between materials is always assumed. However, when the scale is down to nanometer or even smaller, the non-abrupt electron density profile at metal surface causes problems, which are the so called nonlocal effects [2] (wavenumber-dependence) in plasmonics and nanophotonics research. We developed an approach [3] accounting for the non-abrupt surface profile, effectively extending the conventional FDTD method to nonlocal domain. This extension is still within the fast classical calculation scheme, but with the quantum mechanical surface plasmonic effects covered to first order. We utilized this approach to simulate on a few typical nanostructures, and the results on resonance shift and field enhancement agree very well with experiments and other ab initio calculations (e.g. DFT) in literature. |
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H71.00141: Cuboid Arrays as Surface Enhanced Raman Spectroscopy Roshell Lamug, Aftab Ahmed Surface-enhanced Raman spectroscopy (SERS) allows for the enhancement of intrinsically weak Raman signal and thus enables the detection of analytes at single-molecule level and chemical specificity. Despite remarkable advancements in specificity and sensitivity however, SERS still suffers from a loss of signal that depends critically on techniques for nanofabrication. In this project, we use cuboid arrays as an ideal platform for a SERS substrate. This study investigates plasmonic materials and structural parameters of the array to achieve resonant enhancement of the local electric field. Our previous studies, using Finite Difference Time Domain method, revealed promising Raman enhancement factors, approaching 108 using self-assembled arrays of gold nanocubes. These enhancement factors can be further improved with outside parameters such as hybridization of material and using a waveguide arrangement structure. The outcome of this work is the development of a low-cost user-friendly SERS substrate with high sensitivity, and stability. This work will broadly impact the field by assisting in the optimization of powerful multidisciplinary chemical sensing devices. |
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H71.00142: Plasmon-induced efficient hot carrier generation in graphene on gold ultrathin film with periodic array of holes: Ultrafast pump-probe spectroscopy Gyan Prakash, Rajesh Kumar Srivastava, Satyendra Nath Gupta, A K Sood Surface plasmon polaritons (SPPs) due to their inherent property of nanoscale confinement and localization, smaller than the interacting light wavelength, show strong light-matter interaction. Here, using ultrafast transient absorption spectroscopy we show that a high density of hot-electrons can be generated in graphene, through a strong interaction in a hybrid plasmonic structure of graphene with 3D gold hole array. Notably, pump-induced reflectivity shows significant signatures in the spectral window corresponding to extraordinary optical transmission resonances of gold hole array originating from the carrier dynamics in graphene. A comparative study of the graphene on gold film with and without hole array confirms the highly efficient direct plasmon-induced hot carrier generation in graphene. |
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H71.00143: Effect of temperature and defects on the mechanical and electronic properties of stacked van der Waals materials: The example of boron carbo-nitride Siby Thomas, Mohsen Asle Zaeem We demonstrate how the temperature and defects affect the electronic and mechanical properties in van der Waals bound low-dimensional systems, with the example of monolayer boron carbonitride (BCN). Molecular dynamics simulation reveals that as a hetero-structure of h-BN and graphene, the C-C bond in the BCN is responsible for an improved full width at half maximum (FWHM) compared to graphene, which ensures the structural integrity of the BCN monolayer. Besides, consistent with graphene and h-BN, the in-plane lattice parameter of BCN shows thermal contraction over a wide range of temperatures and exhibits a system size dependence. Further, the density functional theory calculations show that electronic bandgap varies substantially (between 0.73 and 1.2 eV) with the presence of Stone-Wales defects whereas it possess metallic character with the presence of vacancy defects. In addition, a tensile test analysis reveals that the elastic modulus and Poisson’s ratio of monolayer BCN are anisotropic and decrease (increase) with the application of uniaxial tensile (compressive) strain which is beneficial for many technological applications. |
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H71.00144: Manipulating charge transfer from core to shell in CdSe/CdS/Au heterojunction quantum dots Exian Liu, Kanishka P Kobbekaduwa, Pan P Adhikari, Ou Chen, Jianbo Gao Core/shell Quantum dots (QDs) or nanorods decorated with metal nanoparticles such as gold (Au) and platinum (Pt) have considerable applications in photocatalysis and optoelectronics. The shell medium plays a key role in tuning charge transfer and recombination process from core to metal domain. However, the study of influence of shell, which addresses the interplay between intrinsic excitons and shell-related surface states in trap-related core/shell/metal QD is currently lacking. In addition, the band offset between the core and shell that relies on temperature parameter also impacts the charge carrier transfer and recombination, but how do charge transfer and recombination vary with temperature still remains unclear. |
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H71.00145: Molecular migration in poly(vinyl alcohol) mixtures Katarzyna Majerczak, Zhenyu Jason Zhang Fluorescence techniques, both Fluorescence Recovery After Photobleaching and Fluorescence Correlation Spectroscopy were used to investigate the migration characteristics of small molecules in thin films composed of poly(vinyl alcohol) (PVA), glycerol and surfactants of various heasdgroup chemistry. We found that the diffusion kinetics of a molecular probe, Rhodamine B, is determined by both molecular arrangement within the film and the magnitude of charged intermolecular interactions. Addition of glycerol initially increases PVA chain flexibility, but inhibits probe movement once its concentration exceeds 44 wt% due to onset of noncompatibility between the two components. The presence of surfactants in the system was found to reduce the diffusivity of RhB in PVA matrix, which is consistent with that in bulk solutions. The reduced diffusion is likely due to steric inhibition for nonionic surfactants. However, the fine balance between inter-molecular interactions and steric inhibition governs the diffusivity of RhB when cationic or anionic surfactants are present in the matrix. |
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H71.00146: Ab initio calculations on the depassivation reaction of H+ at a-SiO2/Si(100) interfaces Pei Li Hydrogen is widely used to passivate the dangling bonds generated in the thermo xidation process, which significantly improves the electronic quality of the Si/SiO2 interface. It may, however, make the devices vulnerable in certain environments. For example, ionization radiation may convert the excess hydrogen induced in the fabrication process to protons, and then the later may migrate to the interface and depassivate the dangling bonds saturated by hydrogen. In this study, the depassivation of Pb1 and Pb0 defects generated in amorphous SiO2/Si(100) interfaces is investigated quantitatively. For Pb1 defects, the proton detaches from the oxygen atom and then activates the defect. The forward reaction barrier is ~0.4 eV. After the reaction, the energy of the system decreases by 0.85 eV. The depassivation of Pb0 defects is more unpredictable, because the proton may be trapped by other atoms or bonds during the long reaction path due to the location of the defect. In our simulation, the proton can be captured by Si-O-Si or Si-Si bond, and form threefold-coordinated O atom defect or Si-H+-Si bridge bond, respectively. The energy of the intermediate products is lower than the desired ones. |
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H71.00147: Perfect absorption in lossy anisotropic materials Sanjay Debnath, Evgenii Narimanov Current state of art for perfect absorption is based on manipulating the incoming wave (which needs to be coherent) or the medium (needs to match impedance at optical frequency) or both. We show (Opt. Express. 27, 9561-9569 (2019)) perfect absorption of incoherent plane wave by planar semi-infinite slab based on the Brewster phenomenon. Lossless isotropic media support Brewster wave but cannot absorb energy. On the other hand, introducing loss in the medium causes Brewster wave to evolve directly into the leaky Zenneck surface wave. We demonstrate that anisotropic media with extra degrees of freedom in material parameters can bring the Zenneck wave back to Brewster wave even in the presence of loss. Our approach identifies potential classes of lossy anisotropic media who support this behavior and shows that the operating frequency of the proposed system is independent of physical dimensions. Our results show that many existing natural materials exhibit this effect at different frequencies from far-infrared to deep ultraviolet regimes. |
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H71.00148: Femtosecond laser-induced structural dynamics of Nickel (111) single crystal. An ultrafast time-resolved x-ray diffraction study. Runze Li, Peter M. Rentzepis Femtosecond, 8.04 KeV x-ray pulses, generated from a table-top system, are used to probe the lattice dynamics of 100 nm and 150 nm Ni (111) single crystals grown on sapphire substrates and irradiated with 800 nm, 100 fs laser pulses. At pump fluencies below the damage and melting threshold, we observed lattice contraction due to the formation of a blast force, and coherent acoustic phonons with a period of 35 ps and 46 ps for the 100 nm and 150 nm Ni (111) films, respectively. The spatiotemporal distribution of electron, spin, and lattice temperatures within the 150 nm thick nickel single crystal was also simulated using the three-temperature model. In addition to the ultrafast heating within the skin depth, this study also revealed the tens of picoseconds time required for heating the hundred nanometer bulk of the Ni (111) single crystal. |
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H71.00149: Magneto-Dielectric investigation in partially disordered Tb2CoMnO6 thin film RAJESH MANDAL, Mohit Chandra, Malvika Tripathi, R.J. Choudhary, Vasily Moshnyaga Relaxor ferroelectrics are recognized as a family of disordered or partially ordered materials that are classified as a special class of dipolar glass with the formation of weakly interacting polarized nano domains (PNR) bellow a certain temperature. They are distinguished from normal ferroelectric materials in terms of broad transition in the temperature dependent dielectric constant and the dispersion of the transition temperature with applied frequency. Here we report the observation of magneto-dielectrically coupled ferroelectric relaxation at quite high temperature (200K) in Tb2CoMnO6/STO(100) double perovskite thin film. Partially B site disordered film has been grown by means of a metal-organic aerosol deposition (MAD) technique. This material is reported as ferromagnetic insulator with TC around 90K. Here we observe an enhanced transition temperature of 110K due to in plane strain. The deviation from the Curie-Weiss law far above TC indicates the development of short range spin correlation which is getting coupled with the electric dipoles present in the system. |
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H71.00150: A comparative study of characteristics of ZnO TFT for various substrate and fabrication parameters Shahidul Asif Several ZnO TFTs (thin-film field-effect transistors) are developed for assessing the characteristics as an FET under different fabrication parameters and substrate materials. These ZnO TFTs are grown using pulsed laser deposition in different substrate temperatures (300-700°C), in different oxygen pressures, and with or without annealing between 400-700°C. The substrates are n-type Silicon with SiO2 insulating layer, and in some samples, they were accompanied by an additional HfO2 film layer as a high dielectric material. All the TFTs have bottom-gate structure while the drain, source, and gates are equipped with gold electrodes fabricated by the sputtering method. The films are analyzed by XRD, Raman spectroscopy and photoluminescence as a verification of the presence of ZnO. Using an experimental set-up, the transfer and I-V characteristics are measured whereas the gate voltage is swept over a range of ~10-50 V. To assess the effectiveness of ZnO material for using in a TFT, the field-effect mobility, the drain current density, etc. are measured. Finally, the TFTs are tested for application in high frequency sweeping (1kHz-1MHz) as the hysteresis nature and power gain cut-off frequencies are compared. |
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H71.00151: Interface Orbital/Charge Reconstruction and Its Effect on Spin Orientation for (110)-La2/3Sr1/3MnO3 Layer Sandwiched by LaCoO3 Films Furong Han, Jirong Sun Here we made the first attempt to reveal the effect of orbital/charge reconstruction associated with interface engineering on spin degree of freedom. We took tensely strained (110)-LaCoO3/La2/3Sr1/3MnO3/LaCoO3 trilayers as specimens, focusing on orbital reconstruction and accompanied effects. The most remarkable finding is the reordering of the energy levels of Mn-3d orbitals: the low-lying orbital becomes dx2-y2 for sandwiched La2/3Sr1/3MnO3 rather than d3z2-r2 as expected for a bare La2/3Sr1/3MnO3 film. Interlayer charge transfer via dx2-y2 orbitals is further detected, which is the driving force for orbital reconstruction. Due to spin-orbit coupling, the charge/orbital reconstruction produces a chain effect on spin degree of freedom of the La2/3Sr1/3MnO3 layer, resulting in a dramatic spin reorientation by 90° in film plane. The present work vividly demonstrates how to tune macroscopic properties of correlated oxides via the mutual coupling between different degrees of freedom. |
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H71.00152: Observation of high electron mobility with significant spin-orbit coupling in rock-salt YbO epitaxial thin film Taku Yamamoto, Kenichi Kaminaga, Daichi Saito, Daichi Oka, Tomoteru Fukumura We report the optical and electrical properties of ytterbium monoxide (YbO) epitaxial thin films with unusual valence state of Yb2+ (4f145d0) [1]. Consistent with the chemical trends of ytterbium monochalcogenides, YbO thin films exhibited the narrow bandgap of 0.25 eV and the large crystal field splitting of 5d orbitals. Electrical resistivity was tunable by electron doping to 5d conduction band via the introduction of oxygen vacancies. Also, electron mobility at 300 K increased up to 13 cm2V–1s–1 with increasing electron carrier density.The weak antilocalization at low temperature observed in the heavily electron-doped YbO suggests significant spin-orbit coupling owing to the heavy Yb nucleus. [1] T. Yamamoto et al., Appl. Phys. Lett. 114, 162104 (2019). Selected as Featured. |
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H71.00153: InN/AlN/Si (111) semiconductor-insulator-semiconductor (SIS) heterostructure for ultrafast optical fibre communication (1550 nm) ARUN CHOWDHURY, Rohit Pant, Basanta Roul, Deependra Kumar Singh, Karuna Kar Nanda, Saluru Baba Krupanidhi In this work, we report on InN/AlN/Si (111) SIS-based self-powered, and ultrafast photodetector, which works at an extremely important wavelength of 1550 nm (fibre communication). InN was grown on AlN/Si template by plasma-assisted molecular beam epitaxy. The heterostructure with a top-bottom (vertical) type of electrode configuration shows a responsivity of 3.36 µA/W with transit times in milliseconds range at zero bias. The variation of photocurrent with respect to power density is nonlinear with an exponent of 1.36, which might be attributed to the presence of traps at the interfaces. To further elucidate the nature of interface of the SIS heterostructure, a low-temperature vertical electrical transport behaviour was studied over a range of 100 – 400 K. It reveals that the barrier height (BH) is inhomogeneous in nature at the hetero-interface. It has been explained by assuming the presence of double Gaussian distribution of BH at the SIS interface based on thermionic emission theory.The double Gaussian distribution of the BH indicated the presence of traps at the interface which was already speculated from the photocurrent and power density relation of the photodetection studies. |
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H71.00154: Graphene Doping in LiMnO4 cathode of Lithium Ion Battery Nnamdi Ene, Erica S Wiley, Mehmet Alper Sahiner Lithium ion batteries, due to their high-power density and high energy are being utilized more and more in present day electronic devices. One way we might improve the absorbance of these batteries is by reducing the band gap energy of the materials used as either the anode or the cathode. Graphene, having a crystalline, 2-dimensional and monoatomic structure has a high electrical conductivity. Graphene is also called a zero-band gap semiconductor. Previous research supports the reduction in the band gap energy by the introduction of graphene as a dopant in thin films. (Elmas et al. 28) This research will thus seek to study the effects of graphene doping in the LiMnO4 cathode region, to electronic energy configuration and the electrical performance of lithium ion thin films prepared by pulsed laser deposition. |
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H71.00155: Self-powered, broadband and ultrafast MoS2/AlN/Si based photodetector Deependra Singh, Rohit Pant, Basanta Roul, ARUN CHOWDHURY, Karuna Kar Nanda, Saluru Baba Krupanidhi Heterostructures of ultrathin 2D layered materials and wide band gap semiconductors offer possibilities of high-performance electronic devices. The absence of a band gap in graphene, which limits its application as a switch, MoS2 has attracted considerable attention in recent years due to its excellent optoelectronic properties, as well as the presence of a narrow band gap. Here, we have reported a self-powered, broadband and ultrafast photodetector based on MoS2/AlN/Si heterostructure. MoS2 thin film has been deposited on AlN template on n-Si(111) by pulsed laser deposition. The vertical transport of the heterostructure exhibits excellent photodetection properties at zero bias condition. The device shows a broadband photoresponse in the range of 300-1100 nm, with a maximum responsivity of 5.47 A/W at 900 nm. Transient analysis of the device at 900 nm shows an ultrafast detection, with rise/fall times of 12.5/14.9 μs. Band alignment studies of MoS2 and AlN has been done by XPS and a band diagram of the heterostructure depicting the self-powered transport has been proposed. |
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H71.00156: Understanding the negative compressibility in a 2D electron gas: Application to LaAlO3/SrTiO3 Aditi D Mahabir, Alexander Balatsky, Jason Haraldsen We investigate the effects of a two-band coupling on the negative compressibility for the two-dimensional electron gas. Using a homogeneous 2D electron model and a two-band description of the electron interactions, we examine the dependence of critical carrier density, dielectric constant, and effective mass on the negative compressibility of the 2D electron gas and compare results to the at the complex oxide interface of LaAlO3/SrTiO3. From our calculations, we show that the presence of interband coupling will produce a dramatic decrease in the polarizability and the critical carrier density of the 2DEG. Furthermore, we find that the ratio of the effective masses of the bands has a distinct and dramatic effect on the negative compressibility. |
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H71.00157: Epitaxial growth and interface band alignment studies of all oxide α-Cr2O3/β-Ga2O3 p-n heterojunction Sahadeb Ghosh, Madhusmita Baral, Rajiv Kamparath, R. J Chowdhury, D. M Phase, S. D Singh, Tapas Ganguli Epitaxial growth of α-Cr2O3(p-type) on c-Al2O3 and β-Ga2O3 (n-type) on α-Cr2O3(p-type) has been carried out to make an all oxide epitaxial n-type β-Ga2O3/p-type α-Cr2O3 heterojunction using RF sputtering. A valence band offset of 3.38 ± 0.2 eV at the heterojunction is determined using Kraut’s method. From the bandgap measurements of α-Cr2O3 and β-Ga2O3, the conduction band offset of 1.68 ± 0.2 eV at the heterojunction is obtained. Thus, the band alignment at this heterojunction is found to be staggered (Type-II), which leads to the confinement of electrons and holes in the β-Ga2O3 layer and α-Cr2O3 layer, respectively. Our results provide a pathway to design all oxide optoelectronic devices based on a p-n heterojunction consisting of n-type β-Ga2O3 and p-type α-Cr2O3. |
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H71.00158: Quantum Correction to the Work Functions of Clean Tungsten Surfaces under Electric Fields Liangliang Xu, Yue Wang, Ming-Chieh Lin, Tsan-Chuen Leung, Hua-Yi Hsu Tungsten has a relatively high work function, electron emission is largely limited. In this work, first-principles calculations are used to study the work functions of tungsten (100), (110), and (111) surfaces under different electric fields. We have carefully and systematically tested the convergence of density-functional-theory (DFT) calculations in the local-density approximation (LDA) and generalized-gradient approximation (GGA) with a plane-wave basis set with the projector-augmented wave (PAW) method as implemented in the Vienna ab initio simulation package (VASP). Detailed study of field emission by using VASP is performed and it is found when we increase the electric field strength, the work functions of tungsten surfaces are reduced accordingly. A new scaling law of work function reduction due to the charge transfer near the metal/vacuum interface caused by external electric field is obtained. The quantum effect is different from the classical Schottky effect of lowering work function due to an external electric field. With the quantum correction, the predictions of Richardson-Dushman and Fowler-Nordheim equations under strong electric fields for thermionic and field emissions, respectively can be improved. |
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H71.00159: Picosecond laser ultrasonic measurements of elastic properties of transition metal dichalcogenides Ethan Murray, Madelaine Pelletier, Jacob Stuligross, Ellis Thompson, Brian Daly, Seng Huat Lee We report ultrafast optical pump-probe measurements of sound velocity and attenuation for GHz frequency longitudinal acoustic strain pulses in MoSe2 and WSe2. High-quality bulk single crystals of 2H-MoSe2 and WSe2 were synthesized by chemical vapor transport with iodine as the transport agent. Thin layers with thicknesses ranging from a few nm up to a few hundred nm were then mechanically exfoliated onto sapphire or SiO2/Si wafers. A degenerate optical pump-probe experiment was performed with a Ti: sapphire ultrafast laser with peak wavelength varied from 760 nm to 830 nm. At these wavelengths, the optical absorption in these crystals is strong enough that a high frequency acoustic strain pulse with frequency components approaching 100 GHz is generated. This picosecond ultrasonic pulse travels back and forth in the exfoliated layer and causes a reflectivity change that is measured by time-delayed probe pulses via the strong strain dependence of the optical properties. Longitudinal sound velocities as well as an upper bound on attenuation of 100 GHz phonons are determined by comparing reflectivity data to 1D simulations. |
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H71.00160: Ab-initio study of surface plasmons on palladium surfaces Unai Muniain, Ruben Esteban, Vyacheslav Silkin Collective electronic excitations at metal surfaces lead to strongly localized electromagnetic fields that play a key role in numerous phenomena in physics, material science, biology or medicine [1]. In particular, surface plasmons are modes that appear in vacuum/metal boundaries, with a constant dispersion relation in the long-wavelength limit predicted by simple models [2]. However, in real metallic systems such predictions often fail. In particular, in many materials, when the non-local behavior of the electronic response is considered, additional collective modes characterized by significantly lower frequencies may appear [3]. In this work, we perform first-principles time-dependent density-functional calculations of the excitation spectra of the palladium surfaces, in order to establish the characteristics of its surface plasmons. We analyze the properties of the surface collective excitations using the surface response function, which is closely related to the permittivity of the material. Our results thus contribute to gaining a better understanding of the optical response of palladium structures. |
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H71.00161: Comparing Magnetron Sputtered ScN Films Grown on Sapphire ((10-10) and (1-102)) Substrates Tobin Muratore, Said Elhamri, Amber Reed, John Cetnar, David C Look, Kurt Eyink, Hadley Smith, Zachary Biegler ScN films with high quality crystal structure and desirable carrier concentration have previously been grown on sapphire (0001) substrates. This study seeks to determine whether similarly high quality films can be grown on (101-0) and (1-102) orientated sapphire. The depositions for this study were carried out via reactive, unbalanced, DC magnetron sputtering. Previous growth of ScN on sapphire (0001) showed film quality is sensitive to sputtering conditions. This study seeks to determine what, if any, sputtering conditions can produce films of comparable quality to those grown on sapphire (0001) substrates on the lower symmetry surfaces. The impact of these growth conditions on the crystal quality and electrical properties were evaluated using x-ray diffraction and Hall-effect measurements. X-ray diffraction results indicate that growth on sapphire (1-102) is sensitive to temperature, with optimal growth occurring in a 40°C window. For (10-10) sapphire, similar crystal quality occurs over temperatures from 500-900°C. XRD also shows no conditions tested for either substrate displayed the single crystal growth present on (0001) sapphire. |
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H71.00162: WITHDRAWN ABSTRACT
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H71.00163: Compression-rate dependent domain growth patterns in diacetylenic chiral lipids Langmuir films: choline vs. ethanolamine head-groups Pritam Mandal In this talk, we discuss domain growth in Langmuir monolayers of two diacetylenic lipids, one with choline and other with ethanolamine head group. We found that (i) Unlike a diacetylenic lipid, Diyne PE (23:2), the diacetylenic Diyne PC (23:2), does not form chiral hierarchal self-assembled patterns. (ii) Structured solid domains in Diyne PC (23:2) Langmuir layer forms within a lower temperature range than with Diyne PE (23:2). Comparing their domain morphology we argue that choline and ethanolamine head groups interact differently with water, influencing the packing-mode. (iii) For both lipids, the growth patterns depend on the compression speed. At lower compression-rate the condensed domains grow as fractal dendrites with straight backbone whereas at rapid compression rate, domains grow as curved claws developing branches as they grow. Since slow or rapid compression rate pushes the monolayer to different non-equilibrium state (different super-saturation), we reason that solid phase grow out of different metastable states, generating distinct morphology. |
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H71.00164: Ultrasonic modification of hydrophobin bubbles and droplets for multiphase systems Zhaoxian Zhang, Paul Russo, Saad Bhamla, Samyak Jain, Udita Ringania Cerato Ulmin(CU), a fungal protein classified as Hydrophobin, is an amphipathic surfactant which self-assembles at interfaces. CU can encapsulate air or oil in aqueous solutions to form non-spherical bubbles or droplets, similar to those formed by interfacial composite materials with solid-like surfaces. A sufficient dispersion of CU in water can create concentrated oil droplet/air bubble structures resembling complex multi-phase systems. These structures, which are observed to be stable for days, could have a variety of applications in emulsion engineering, reaction catalysis, and constructing multi-scale metastructures, among many others. Ultrasonic agitation was used to modify these structures, and it was discovered that the frequency of the ultrasound corresponded to the length scale of air-filled structures, by mechanism of Minnaert Resonance. With this method it was possible to select the size distribution of the air-filled structures. Oil-filled structures behaved differently, yet with sufficient ultrasound amplitude, it was possible to produce CU-oil nano-emulsions, likely by the mechanism of cavitation. The size and longevity of these nano-emulsions were studied by dynamic light scattering. |
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H71.00165: Scanning Probe Microscopy of Two Dimensional Covalent Organic Frameworks Harshavardhan Murali, Zachery Enderson, Cameron Feriante, Raghunath Dasari, Hong Li, Simil Thomas, Timothy C Parker, Jean-Luc E Bredas, Seth R. Marder, Phillip N First Covalent organic frameworks (COFs) are a new class of materials that can be designed to exhibit interesting physical, chemical and electronic properties. In this work, we study the growth and properties of single layer covalent organic frameworks that we synthesize on noble metal surfaces, typically via an Ullmann-like process accomplished through thermal deposition and annealing. An outstanding challenge in 2D-COF on-surface synthesis is to achieve long range, defect free crystalline order over hundreds of nanometers. Using scanning tunneling microscopy (STM), we probe COF growth and island formation under different preparation conditions, from monomer self-assembly to covalent bond formation. We also study the electronic properties of COF islands obtained in this process, including effects of finite size and substrate interaction, using scanning tunneling spectroscopy and comparisons to theoretical first-principles calculations. |
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H71.00166: Nanotribology of Phosphonium Phosphate Ionic Liquid: a Combined Atomic Force Microscopy and Surface Spectroscopy Study Filippo Mangolini, Zixuan Li, Oscar Morales-Collazo, Jerzy T. Sadowski, Hugo Celio, Andrei Dolocan, Joan Brennecke Ionic liquids (ILs) have recently gained considerable attention owing to their unique and tunable properties (e.g., wide electrochemical window, high thermal stability), which make them potentially useful for a range of applications, including batteries, fuel cells, catalysis, and lubrication. When IL are used as lubricants, the interface between the IL and the solid surface plays a pivotal role to determine the friction/wear response. Despite the weight of the studies published in the literature, remarkably little is still known about the structure of solid/IL interfaces and its relationship with the lubrication mechanism/performance of ILs. |
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H71.00167: WITHDRAWN ABSTRACT
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H71.00168: Planar polymers under cylindrical confinement Dulce Valencia We show that the cylindrical confinement of a planar ribbon gives rise to the formation of stationary helical shapes, previously observed in molecular dynamics simulation studies of some planar polymers inside nanotubes. In the limit of small twisting deformations, we notice that a confined ribbon describes identical equilibrium configurations of an elastic rod on the plane. Also, every locally planar strip adsorbed on a cylinder is forced to follow a helical envelope, as its length increases. We also determine the forces and torques that sustain each ribbon equilibrium configuration through the equilibrium geometry and the confinement surface parameters. |
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H71.00169: SAMPLE: Surface structure search enabled by coarse graining and statistical learning Lukas Hörmann, Andreas Jeindl, Alexander T. Egger, Michael Scherbela, Oliver T. Hofmann
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H71.00170: Effects of Ligand Composition on Protein Corona Formation around, and the Surface Structure of, Au Nanoparticles Sam Hoff, Desiré Di Silvio, Sergio Moya, Ronald Ziolo, Hendrik Heinz Coatings on nanoparticles in biological environments greatly impact the dynamics and stability of the nanoparticles. Destinations, and potential function of nanoparticles can be changed by attaching ligands to the nanoparticle surface. In this study, molecular dynamics is used to study how different ligands, and specifically different chemical end groups, alter the surface structure and dynamics of the ligands in solution. PEG2000, Alkyl-PEG600-Glucosamide, and Alkyl-PEG600-Butanamide and their specific interactions with Bovine Serum Albumin and Concanavalin A are studied in detail. The effects of altering the end group on Alkyl-PEG600-Butanamide to Propanamide and Ethanamide are explored, and is found to have a significant impact on the surface structure at the ligand-water interface, potentially altering nanoparticle interactions in solution, as well as protein corona formation. The CHARMM36-Interface force field is used throughout all simulations which yields interfacial properties directly comparable to experimental measurements. The study is expected to lead to new insight into how protein-ligand interactions work, as well as advancing understanding of how ligand conformations can affect their environmental interactions. |
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H71.00171: Selective studies of adsorption of Ag8M and Ag14M clusters (M = Au, Co and Pt) on alumina substrate Isabella Levensohn Kastor, Nusaiba Zaman, Abdelkader Kara Small silver clusters were used as catalyst for Li-air batteries, which controlled the rate of discharge at the cathode. The gap near the fermi energy was shown to control the oxygen reduction, an important reaction for LiO2 formation. One can vary the size of the cluster to vary the gap, however, this “knob” provides limited variance. Hence, we study the effect of alloying in combination with size variation of Ag8M and Ag14M clusters (M = Au, Co and Pt). Using Density Functional Theory (DFT), we determine the most stable geometry of these bimetallic clusters and calculate the binding energies of these clusters on the alumina substrate. We explore how the gap at the Fermi level of the system varies as a function of elemental composition and size of the cluster. Bader charge analysis is also performed to probe how the charges are transferred between the cluster and the substrate. These preliminary studies will open the door for more systematic studies of alloy clusters of different size and stoichiometry for Li-O2 battery cathode design as well as for general catalysis. |
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H71.00172: Structural and magnetic transition in NiO(111) surface Wandong Xing, Yang Zhang, Fanyan Meng, Jing Zhu, Rong Yu We report an experimental and theoretical analysis of the NiO(111) surfaces combining aberration corrected TEM and first-principles calculations. An unreconstructed O-terminated (1×1) surface and a reconstructed O-terminated surface (with the topmost Ni in tetrahedral sites, a wurtzite-like surface stacking) have been revealed. Here, the two surfaces are shown to be stabilized by charge compensation, arising from changing the valence state of the topmost Ni2+ into Ni3+ ions and providing the additional positive charges to the surface. In addition, it is found that the main difference between the two surface structures is the movement of the topmost Ni atoms from octahedral position to tetrahedral position, coupling to a spin transition from the low-spin state (Ni3+-LS) to the high-spin state (Ni3+-HS). |
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H71.00173: Using Machine Learning to Understand Mechanical Loss in LIGO Mirror Coatings Sagada Penano, Kiran Prasai, Jun Jiang, Alec Mishkin, Hai-ping Cheng, Riccardo Bassiri, Martin M. Fejer The sensitivity of future generations of gravitational wave detectors such as LIGO will be limited by thermal noise from the mirror coatings on the test masses. A major source of thermal noise is the mechanical loss of the coatings. The mechanical loss at temperatures higher than 10 K is believed to be the result of thermally activated transition between two level systems (TLSs) in the amorphous coating. By using a multilayer perceptron neural network to understand the atomic structures of many computer-generated two-level systems (TLS) of amorphous tantala (a-Ta2O5), a prospective coating material, we aim to identify the structural motifs that contribute to mechanical loss. From an analysis of many independent TLSs, we can identify which atoms are most likely to relax by comparing changes in atomic energies and positions. Values that describe the structural features of these atoms can then be computed using angular and radial distribution functions. Using these predictions, a common pattern of relationship between structure and relaxation behavior can be extracted. The results will likely aid in understanding what gives rise to the measured values of mechanical loss and will help determine the best materials and deposition parameters for lower mechanical loss mirror coatings. |
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H71.00174: Invalidity of the BCS theory of superconductivity Jorge Hirsch A theory that purports to describe the natural world can be proven invalid by either (a) an experimental result or (b) a theoretical proof that it is internally inconsistent. However BCS is special: it cannot be disproved by (a) because any superconductor yielding an experimental result that doesn't conform to BCS is simply declared to be 'unconventional'. Hence we are left with (b). In a process where the temperature of a type I superconductor in a magnetic field changes, the London penetration depth and hence the magnetic flux changes, generating a Faraday electric field. BCS theory predicts that the electric field gives rise to a normal current and as a consequence Joule heat is dissipated, in an amount that depends on the speed of the process, and it also predicts that the final state is independent of the speed of the process. I show that these two predictions cannot be simultaneously reconciled with the laws of thermodynamics. Therefore, BCS theory is internally inconsistent. I propose a resolution of this conundrum through physics that is not part of BCS theory. |
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H71.00175: WITHDRAWN ABSTRACT
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H71.00176: Numerical solution of the full-bandwidth Eliashberg equations including vertex corrections beyond Migdal's approximation Alex Aperis, Fabian Schrodi, Peter Oppeneer We solve the full bandwidth and non-adiabatic Eliashberg equations for electron-phonon mediated superconductivity by fully including the first vertex correction in the electronic self-energy. The non-adiabatic equations are solved numerically without further approximations for a generic one band model system. We compare the results with outcomes of adiabatic Eliashberg calculations. Non-adiabatic contributions can increase, decrease or have negligible effect to the superconducting gap depending on the dimensionality of our system, the degree of non-adiabaticity and the coupling strength. We further examine effects on the transition temperature and the electron-phonon coupling constant. Our treatment opens up the possibility of systematically studying vertex correction effects in strongly coupled and/or adiabatic superconductors, such as the ones with high transition temperature. |
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H71.00177: Melting transition of the nematic state in an under-doped d-wave superconductor Hong-Yi Chen, Yu-Yo Chen We study the melting transition of smectic state in an under-doped d-wave superconductivity. We demonstrate that the transition is discontinuous to the nematic state by increasing the impurities. We calculate the entropy as a function of impurities which shows a sharp transition between the smectic and nematic states. We also show that the density-of-states at the Fermi energy emerges as the sub-gap induced by the SDW order is smeared out gradually. The transition between the smectic and nematic states is associated the reconstruction of the electronic Fermi surface. We calculate the superfluid density that exhibit a plateau and indicates that the nematic state development in d-wave superconductor is distinct from high-temperature pseudogap. |
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H71.00178: Finding the static critical exponent in YBa2Cu3O7 using critical current density Ioan Dascalu, Matthew C. Sullivan We grew thin films of hole-doped cuprate YBa2Cu3O7 (YBCO) using optimized pulsed laser deposition and patterned them into a meander wire with conventional photolithography techniques. We examined the normal-superconducting phase transition of the thin films via a critical scaling analysis of voltage vs current isotherms, where each measurement is the average of many reverse-polarity measurements. We expect the superconducting phase transition to obey critical (3D-XY) theory near the critical temperature and obey mean-field theory further from the critical temperature. We show that critical current density can access both the critical regime and the mean-field regime in a single sample. We present our results on the static critical exponent in both regimes for YBCO. |
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H71.00179: Transport characteristics of type II Weyl semimetal MoTe2 thin films grown by chemical vapor deposition Niraj Bhattarai, Anderw W Forbes, Rajendra Dulal, Ian L Pegg, John Philip Theoretical calculations and experimental observations show MoTe2 is a type II Weyl semimetal, along with many members of transition metal chalcogenides family. We have grown highly crystalline large-area (upto 8mm X 4mm ) MoTe2 thin films on Si/SiO2 substrates by chemical vapor deposition. Very uniform, continuous, and smooth 1T'-MoTe2 films were obtained as confirmed by scanning electron microscopy, atomic force microscopy, x-ray and Raman spectroscopy analyses. Measurements of the temperature dependence of longitudinal resistivity and current-voltage characteristic at different temperature are discussed. Unsaturated, positive quadratic magnetoresistance of the as-grown thin films has been observed at various temperatures below room temperature. Hall resistivity measurements confirm the majority charge carriers are holes. Using the single band model, carrier concentration was calculated to be 2.38 × 1021 holes cm-3 at 10 K, which is semimetallic, and increasing with temperature. These results will guide us in the way of pragmatic applications of thin films MoTe2 in future electronic devices. |
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H71.00180: WITHDRAWN ABSTRACT
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H71.00181: "Thickness dependent characteristics of Single Crystalline Bi:YIG Thin Film grown with different orientation" GANESH GURJAR, VINAY SHARMA, Satyabrata Patnaik, Bijoy Kuanr The Magneto-Optical (MO) properties are increases when bismuth (Bi) is substituted in the YIG (Bi0.1Y2.9Fe5O12 , BYIG). BYIG films of two different thickness were grown with different orientation ([111] and [100]) by pulsed laser deposition (PLD) technique over single crystalline Gadolinium gallium garnet (GGG) substrates. The BYIG grown with [100] orientation was observed structurally better with lesser strain (around 40% lesser). As the thickness of film decreases, the size of lattice parameter is also slightly decreases and it is more (by 0.073%) for the film grown over GGG having [111] plane. Larger ferromagnetic resonance (FMR) line width is observed in [111] directed film (100 Oe) as compared to [100] directed film (60 Oe) and also it decreases with the film thickness (100 Oe to 47 Oe in [111] and 60Oe to 39 Oe in [100] directed film). The value of net effective magnetization and Gilbert damping constant is observed to be increases with decrease in thickness of the film. The low Gilbert damping constant (1.53×10-4, [100]) is observed as compared with (2.68×10-4, [111]). Thus BYIG thin film grown on GGG along [100] direction shows better structural and magnetization characteristics and hence can be used for microwave devices such as microwave filter etc. |
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H71.00182: Study of V/TiO2 interface by X-ray Photoelectron Spectroscopy Miranda S Martinez, Anil Chourasia The V/TiO2 interface has been studied by the technique of x-ray photoelectron spectroscopy (XPS). Thin films of titanium were deposited on a quartz substrate and oxidized in situ to form TiO2 overlayer. Thin films of vanadium were then deposited onto this TiO2 substrate. The samples were annealed at 100, 200, 300, 400, and 500°C for fifteen minutes and were analyzed in situ by XPS. The titanium 2p, the vanadium 2p and the oxygen 1s core level analyzed for this purpose. The aluminum x-rays (energy = 1486.6 eV) were used as the source of excitation. The spectral data have been recorded at 45 degree take-off angle. The spectral data have been analyzed to estimate the chemical reactivity at the V/TiO2 interface. The spectral features (shift in the core levels and the shape of the core level peaks) have been utilized. The chemical reactivity as a function of the thickness of the vanadium overlayer and the annealing temperature has been established and will be presented. |
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H71.00183: Aun cluster deposited on a TiO2 (110) slab Pablo De la Mora, Gustavo Tavizon, Esther Agacino The unreactiveness of gold breaks down in the nanoscale, where it has a very strong catalytic activity. To study this, Au atoms are added in the 110 surface of the rutile, TiO2. In this study gold atoms are added one by one to the surface and different configurations are energetically optimized. The objective is to study how the atoms interact with the rutile surface and when the 2D to the 3D transition happens. The Au4 cluster deviates from the flat rhombus, thus beginning to have a 3D character, it is in the Au5 where the 3D character is clearly obtained, forming triangular bipyramid. The study was done using the WIEN2k package |
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H71.00184: Synthesis, Crystallography, Microstructure, Crystal defects and Optical Properties of (Fe-Ni) co-doped ZnO Thin Films prepared by sol–gel technique Ahmad Alsaad, Qais Al-Bataineh, A. Ahmad, A. Bani-Salameh, Zaid Albataineh, Ahmad Telfah Zinc oxide (ZnO) and Iron-Nickel Fe-Ni co-doped ZnO thin films have been doped coated in glass sustrate using Sol Gel technique. |
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H71.00185: Adsorption And Diffusion Properties of Aromatic Molecules on Silica/Ru(0001) Muhammad Sajid, William Kaden, Abdelkader Kara Now a days, organic materials are replacing the conventional Si based ones in electronic devices due to being cheap, light weight and flexible. These devices are manufactured with metal contacts at both ends, providing support and/or electric conduction. Electronic properties at both ends are changed due to charge transfer at the interface affecting performance. In order to control charge transfer, we are investigating effects of inserting an inert layer separating the two. Using DFT with added vdW corrections and surface science spectroscopic techniques (XPS, LEED etc), we are studying adsorption of aromatic molecules on Ru(0001) with and without silica layer in between. Silica layer is shown to greatly inhibit adsorption strength and charge transfer at the interface. Using CI-NEB (Climbing Image Nudge Elastic Band) and TPD (Temperature Programmed Desorption) measurements, diffusion characteristics of molecules through pores of silica sheet and under the layer are thoroughly discussed. Comparison of simulation and experiment can provide better understanding of important processes at the interface. |
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H71.00186: Linking sprayability to thin-film performance in CNT-redox-polymer dispersions Karthika Suresh, Stephen Cotty, Xiao Su, Michelle A Calabrese Carbon nanotube (CNT)-loaded redox-polymer coatings are an attractive class of composite materials for charge storage devices, high-surface area ion-binding platforms, and selective redox mediated separation systems. While CNTs provides a nanoporous conductive network, the electroactivity of the redox-polymers grants these systems high pseudocapacitive charge-storage and ion recognition properties. Metallopolymers in particular are attractive due to their fast electron-transfer, synthetic tunability, and reversibility. However, processing CNT-metallopolymer dispersions to form uniform thin film coatings on large length scales is a substantial challenge. The sprayability, coatability, and printability of these dispersions are dictated by the extensional flow properties. Here, we link the extensional flow properties to the quality of the solution-processed thin film using capillary breakup extensional rheometry (CaBER) to capture filament formation and breakup. The CNT: polymer ratio, polymer molecular weight, polymer chemistry and solvent quality all impact the extensional rheology and corresponding thin film quality. Our results show a strong link between macroscopic flow properties, dispersion processability and final thin-film performance on the electrodes. |
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H71.00187: Oxidation of Tin as investigated by X-ray Photoelectron Spectroscopy Allen Hillegas, Anil Chourasia The oxidation of tin has been investigated by the technique of x-ray photoelectron spectroscopy. Thin films of tin were deposited on a silicon substrate by the e-beam technique. The films were oxidized in situ by exposing them to an atmosphere of oxygen at temperatures of 100, 200, 300, 400, and 500°C for various times. Aluminum x-rays (energy = 1486.6 eV) were used to record the spectra. The tin 3d and oxygen 1s core levels have been investigated. The spectral data (binding energy shift and the shape of the core level peaks) have been utilized to interpret the data. The growth of the oxide as a function of the substrate temperature and the oxygen pressure has been evaluated. The oxidation kinetics have been modelled to follow the growth of the oxide. |
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H71.00188: Fabrization of giant piezoelectric material Sm-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal film Yifei Fang, Min Xu, Yin Hang Sm-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Sm-PMN-PT) single crystal was recently reported as a new piezoelectric material with the highest piezoelectric charge coefficients which will have great applications on transducers and sensors in electromechanics [1]. In previous research, the piezoelectric mechanism in the material is believed that the local structural heterogeneity of relaxor ferroelectric crystals caused by Rare-earth element. However, the research on the thin film of this material is still lack. For further investigate the piezoelectric properties of Sm-PMN-PT thim film, we explored the methods to grow Sm-PMN-PT film on different substrates, such as YAlO3, MgAl2O4, MgO. Furthermore, we analyzed and compared the differences in the transport properties and crystal structure between Sm-PMN-PT layers deposited onto different substrates. According to the calculation in Ref. [1], La3+ and Nd3+ was considered substituting the Sm ions in our future work. This research will promote the development of advanced piezoelectric devices. |
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H71.00189: Fabrication of (Ga2O3)x(Fe/Cr)y(ZnSeTe /ZnSTe)1-x-y film on quartz substrate Yifei Fang, Shulong Zhang, Min Xu, Yin Hang Mid-IR (MIR) band at ~3μm has attracted much attention for their wide applications in medical, biological, sensing technologies, etc. Ga2O3 is a wide band gap semiconductor material with fine electrical and luminescent properties, which has been widely used in photoelectric devices. Recently, an intriguing material (In2O3/Ga2O3)0.1(Co)0.5(ZnS/Se)0.4 has been reported[1] that which owns better optical and transport properties than its parent phase of Ga2O3 and In2O3. According to Ref [1], the reason of doping Co was the rich absorption and emission levels, good infrared optical properties, and room temperature ferromagnetic (RT-FM) property. However, compared with Co, transition metal Fe and Cr have wider FWHM of absorption, emission and luminescence spectrum, and even Fe has stronger RT-FM property than Co. Moreover, the different chalcogenide elements substitution might induce abundant properties which has been already verified by many researches in correlated system[2]. Hereby, we synthesized (Ga2O3)x(Fe/Cr)y(ZnSeTe /ZnSTe)1-x-y film onto quartz substrate and investigated the structure, optical and transport properties. |
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H71.00190: A route to atomically flat TiO2 terminated surfaces in SrTiO3avoiding HF acid. Dakota Brown, James Payne, Maitri Warusawithana SrTiO3, known as a quantum paraelectric, is a very interesting quantum system. At the same time it is a widely used substrate to grow epitaxial oxide thin films. For the growth of high quality films and superlattices, it is imperative to have an atomically flat starting surface with a known surface termination. While the main technique for obtaining quasi-ideal SrTiO3 surfaces for growth of epitaxial thin films has been via an etching step that involves HF acid [Appl. Phys. Lett. 73, 2920 (1998)] followed by an anneal in flowing oxygen to around 1000 C, here we discuss an alternate process for obtaining atomically flat surfaces. Our process involves etching in a dilute HCl acid solution, which is known as a polishing etch for SrTiO3, and eliminates the use of HF acid and the need for the high temperature (1000 C) anneal. We will compare atomic force microscopy and RHEED images of SrTiO3 substrates prepared with our process involving dilute HCl acid with those prepared using the method involving HF acid. Our controlled experiments suggest that this process provides extremely smooth surfaces with very sharp step edges that are mostly oriented parallel to the crystallographic axes. |
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H71.00191: Intrinsic magnetic topological insulator phases in the Sb doped MnBi2Te4 bulks and thin flakes Bo Chen, Fucong Fei, Fengqi Song Magnetic topological insulators (MTIs) offer a combination of topologically nontrivial characteristics and magnetic order and show promise in terms of potentially interesting physical phenomena such as the quantum anomalous Hall (QAH) effect and topological axion insulating states. However, the understanding of their properties and potential applications have been limited due to a lack of suitable candidates for MTIs. Here, we grow two-dimensional single crystals of Mn(SbxBi(1-x))2Te4 bulk and exfoliate them into thin flakes in order to search for intrinsic MTIs. We perform angle-resolved photoemission spectroscopy, low-temperature transport measurements, and first-principles calculations to investigate the band structure, transport properties, and magnetism of this family of materials, as well as the evolution of their topological properties. We find that there exists an optimized MTI zone in the Mn(SbxBi(1-x))2Te4 phase diagram, which could possibly host a high-temperature QAH phase, offering a promising avenue for new device applications. |
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H71.00192: Gate-controlled anomalous Hall effect reversal in the magnetic topological insulator MnBi2Te4 device Shuai Zhang Magnetic topological insulator, a platform for realizing quantum anomalous Hall effect, axion state and other novel quantum transport phenomena, has attracted a lot of interest. Recently, it is proposed that MnBi2Te4 is an intrinsic magnetic topological insulator, which may overcome the disadvantages in the magnetic doped topological insulator, such as disorder. Here we report on the gate-reserved anomalous Hall effect (AHE) in the MnBi2Te4 thin film. By tuning the Fermi level using the top/bottom gate, the AHE loop gradually decreases to zero and the sign is reversed. The positive AHE exhibits distinct coercive fields compared with the negative AHE. It reaches a maximum inside the gap of the Dirac cone, and its amplitude exhibits a linear scaling with the longitudinal conductance. The positive AHE is attributed to the competition of the intrinsic Berry curvature and the extrinsic skew scattering. |
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H71.00193: Preparation of Few quintuple layers Bismuth selenide (Bi2Se3) by spin coated-coreduction approach (SCCA) and Optical nonlinearity was discussed Wei-Heng Sung, Hsuan-Sen Wang, Yue Zhou, Hong Liu, Chao-Kuei Lee Topological insulators (TIs) have been realized their functionality of saturation absorption (SA) for pulsing lasers. Recently, using spin coated-coreduction approach (SCCA) growth Bi2Te3 thin film, continuous wave mode locking (CWML) solid state laser with repetition rate as high as GHz has been demonstrated. Compared to Bi2Te3, Bi2Se3 has been theoretically and experimentally investigated with p-type nature, leading to greater potential to be a SA. However, the difficulty of preparing high optical thin film results in the less report about their application for pulsed lasers. In this study, large area topological insulator thin film Bi2Se3 (Bismuth Selenide) of few quintuple layers were prepared by spin coated-coreduction approach (SCCA). AFM image, TEM image, XPS, XRD, Raman pattern all show that the growth Bi2Se3 thin film is with high crystalline quality. In addition, the application of Bi2Se3 for pulsing solid state laser was studied and discussed as well. |
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H71.00194: Role of polarization force for coherent phonon generation within the Bi2Te3 thin film Meng-Ching Lee, Tsun-I Chen, Jin-Wei Li, Chao-Kuei Lee To date, the generation mechanism of coherent phonon within the topological insulators is an important but still unconfirmed topic. In this work, using double pulse technique, the dynamic properties and possible mechanisms of the coherent phonon(A1g1 , A1g2, Eg2) in Bi2Te3 were investigated. Among these three phonon modes, decreasing intensity and frequency as increasing temperature was observed, which can be attributed to the reducing temperature gradient, leading to thermal force generation mechanism. However, by analyzing the temporal evolution of the phonon frequency, the frequency of Eg2 was gradually shifted to higher frequency rather than red shift trend observed in the A1g1 and A1g2. This indicates that an additional way for generating Eg2 mode with nature of an-harmonicity might be inevitable. Here, the polarization force mechanism for Eg2 mode was proposed and discussed in detail. |
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H71.00195: Strain induced tuning and annihilation of Dirac point in the topological insulator Bi2Se3 (001) surface. Soumendra Das, Prahallad Padhan Engineering the band gap and tuning the Dirac point (DP) of (001) surface of the 8 quintuple layers (QLs) thick Bi2Se3 were investigated by varying the strain through first principle density functional theory calculations, with and without the presence of spin-orbit coupling (SOC). The strain on the Bi2Se3 (001) surface primarily varies the band width, which changes the orbital pupulation in the conduction and valence band. The tuning of the pz - orbital population of Bi on the (001) surface of the Bi2Se3 froms the Dirac cone at the Γ point, which can be achieved under uniaxial, biaxial or volume conservation strain. Around 6% out-of-plane tensile strain annihilates the DP of the (001) surface of the Bi2Se3 which causes the loss of topological surface states. The anniliation of the DP occurs even at lower values of volume conservation strain. However, the DP feature is preserved for the entire range of biaxial strain. The DP moves towards the Fermi level for the increasing tensile strain under unixial and volume conservation configuration, but the similar displacement of DP occurs due to increasing compressive biaxial strain. The tuning of DP may provide a new pathway to control many physical properties of Bi2Se3 and shed light for its technological applications. |
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H71.00196: WITHDRAWN ABSTRACT Donna Greene
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H71.00197: Core Reconstruction of Dislocations in layered-chalcogenide semiconductors (Bi2X3 - X = Te, Se, and S) Nestor Fajardo, Ricardo Nunes The interest in the layered chalcogenide family Bi2X3 (X = Te, Se, and S) is due to their |
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H71.00198: WITHDRAWN ABSTRACT
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H71.00199: Refinement of High-Throughput Calculations for Rare Earth Topological Insulators Gavin Nop, Jonathan Smith Topological Insulators (TI) have become increasingly important in the condensed matter science of electronic band theory. We focus on inorganic topological insulators using advancements in “Topological Quantum Chemistry” (TQC) [Bradlyn et al., Nature 547, 298 (2017)], combined with “A Complete Catalog of High-Quality Topological Materials” [Vergniory et al., Nature 566, 480 (2019)], to narrow our search to predicted topological insulators. In the latter paper, a high-throughput calculation of electronic band structure was used to predict TI’s. The inorganic topological materials were down-selected to rare earth materials which require on-site electron correlation and spin orbit coupling to verify their band topology. To keep computations feasible, we restrict our materials search to binary and ternary compounds with appropriate crystal structures. Rare earth materials require high-quality density functional theory calculations in order to compute their electronic band structure. We produce such high-quality calculations for a down-selected representative set of rare earth crystals in order to refine and correct the TQC high-throughput predictions. G.N. is grateful for an assistantship in the US DOE Office of Science, Science Undergraduate Laboratory Internship program. |
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H71.00200: Aubry-Andre-Harper Model with on-site hopping and p-wave pairing Mohammad Yahyavi, Balazs Hetenyi, Bilal Tanatar We study an extended Aubry-André-Harper model with simultaneous modulation of hopping on-site potential and p-wave superconducting pairing. For the case of commensurate modulation of β=1/2 it is shown that the model hosts four different types of topological states: Adiabatic cycles can be defined which pump particles two types of Majorana fermions or Cooper pairs. In the incommensurate case we calculate the phase diagram of the model in several regions. We characterize the phases by calculating the mean inverse participation ratio and perform multifractal analysis. In addition we characterize whether the phases found are topologically trivial or not. We find an interesting critical extended phase when incommensurate hopping modulation is present. The rise between the inverse participation ratio in regions separating localized and extended states is gradual rather than sharp. When in addition the on-site potential modulation is incommensurate we find several sharp rises and falls in the inverse participation ratio. In these two cases all different phases exhibit topological edge states. |
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H71.00201: Dipolar Magnetoexcitons in α-T3 double layers in a high magnetic field Yonatan Abranyos, Godfrey Gumbs, Oleg Berman We consider two parallel α-T3 layers separated by an insulating slab (e.g. SiO2 or a hexagonal boron nitride (h-BN) insulating barrier) in a high magnetic field. The equilibrium system of local pairs of electrons and holes, spatially separated in these parallel α-T3 layers, correspondingly, can be created by varying the chemical potential using a bias voltage between two α-T3 layers or between two gates located near the corresponding α-T3 sheets (case 1) (for simplicity, we also call these equilibrium local e-h pairs as dipolar magnetoexcitons). In case 1 a dipolar magnetoexciton is formed by an electron on the Landau level 1 and hole on the Landau level −1. Dipolar magnetoexcitons with spatially separated electrons and holes can be created also by laser pumping (case 2) and by applying a perpendicular electric field. In case 2, a dipolar magnetoexciton is formed by an electron in the Landau level 1 and hole in the Landau level 0. We assume the system is in a quasi-equilibrium state. We study the collective properties and superfluidity of dipolar excitons in α-T3 double layers in a high magnetic field for both case 1 and case 2. |
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H71.00202: Smooth Evolution in Hall Coefficient in the Overdoped Cuprate Tl2201 Carsten Putzke, Siham Benhabib, Wojciech Tabis, Jake Ayres, Liam Malone, Nigel Hussey, John R. Cooper, Antony Carrington Our understanding of the microscopic origin of superconductivity in the cuprates is dependent on our knowledge of the normal state. Recently a sharp transition in the carrier density was proposed, close to optimal doping in YBa2Cu3O6+δ and Nd-doped La2-xSrxCuO41,2. This transition was argued to be tied to the Pseudogap endpoint p*. |
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H71.00203: Exploring the Josephson Scanning Tunneling Microscopy: Towards a Phase-Coherent Junction Michael Dreyer, Joseph Murray, Wan-Ting Liao, Sudeep Dutta, Christopher J Lobb, Frederick C Wellstood, Robert E Butera Josephson scanning tunneling microscopy (JSTM) is performed by using a superconducting tip on a superconducting sample. The resulting Josephson junction (JJ) is usually too small in terms of critical current and capacitance to support phase coherence between the two superconductors. We are pursuing a concept to overcome that limitation by stabilizing the phase in the scanning junction with a larger JJ in a SQUID loop. We employ a home-built dual-tip STM with connected tips to implement the concept. We characterize the individual junctions by measuring standard I(V) and dI/dV curves, as well as V(I) characteristics which are more common to the study of JJs. In the SQUID configuration, a flux bias of the SQUID should lead to a modulation of the critical current, thus proving the concept. |
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H71.00204: MATERIALS PHYSICS
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H71.00205: Mapping out the electronic and magnetic transitions in mixed-valent La1-xSrxMnO3 thin films James Payne, Dakota Brown, Thomas Pekarek, Maitri Warusawithana The rich phase diagram in mixed-valent manganites has been intensely studied in bulk crystals as a function of chemical doping. Here we study the effect of doping in La1-xSrxMnO3 thin films by varying the Sr/La ratio between samples. These thin films are grown using ozone assisted molecular beam epitaxy with carefully controlled stoichiometry for a range of doping from x = 0.0 to x = 0.5. Our electronic measurements reveal a crossover from a Mott insulator to a metallic ground state as x is increased. In the metallic ground state we observe a metal-to-insulator transition coincident with a ferromagnetic-to-paramagnetic ordering transition consistent with the double exchange interaction with higher, doping dependent transition temperatures compared to those reported for bulk La1-xSrxMnO3 crystals. We will also discuss the magnetic ordering transitions observed in the low doping regime (x<0.17) where an insulating ground state is observed and compare these transitions with those reported for bulk La1-xSrxMnO3 crystals. |
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H71.00206: Temperature-dependent Raman studies of a natural van der Waals heterostructure Viviane Zurdo Costa, Sam Vaziri, Shirin Jamali, Addison Miller, Andrew Ichimura, Eric Pop, Akm Shah Newaz Van der Waals heterostructures (vdWH) comprised of two-dimensional (2D) materials offer a platform to obtain designed materials with unique electronic properties. Research on 2D vdWH has so far been focused on fabricating such heterostructures by stacking individual 2D crystals, which leads to stacks with the presence of fabrication defects. Franckeite (Fr) is a naturally occurring vdWH comprised of two different alternately stacking semiconducting layers, that enables the study of a complex layered system where the crystal orientation between layers has been preserved. Unlike other layered sulfide-based materials, Fr is a grained-textured rock composed of few-millimeter flakes in random orientation. For this reason, exfoliation of thin flakes with a uniform and large surface area for optical characterization and transfer techniques is especially challenging. By precise manipulation of the starting flake in combination with different substrates we were able to increase the quality of exfoliation and obtain few-layer (< 5) Franckeite flakes with uniform surface areas of approximately 5 μm. Here we present results on the developed exfoliation technique and temperature-dependent Raman spectroscopy of Franckeite. |
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H71.00207: Magnetism-induced Raman modes in two-dimensional CrI3 atomic layers Gaihua Ye, Zhipeng Ye, Rui He, Hyun Ho Kim, Bowen Yang, Adam Tsen, Wencan Jin, Siwen Li, Liuyan Zhao We studied CrI3 atomic layers down to the monolayer limit using temperature and magnetic field dependent micro-Raman spectroscopy. Two sets of Raman modes at frequencies of ~76 and ~125 cm-1 are observed in CrI3 atomic layers only in the antisymmetric channel below the magnetic phase transition temperature, suggesting that these two modes are related to the broken time reversal symmetry in the samples. By tracking the thickness dependence of both modes, we reveal that they are of the surface nature. Magnetic field dependent measurements of bilayer CrI3 at 10 K further show that these modes disappear above the critical field of ~0.8 T. Possible origin of these two Raman modes is proposed. |
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H71.00208: Strain tuned structural phase transition and optical switching in 1T-ZrS2 and 1T-ZrSe2 Edoardo Martino, Florian Le Mardelé, Konstantin Semeniuk, David Santos-Cottin, Francesco Capitani, helmuth berger, Laszlo Forro, Ana Akrap Strain is a versatile and powerful tool to manipulate electronic properties of 2D-materials. In addition to continuous tuning of the electronic band-structure, applied strain can drive a structural phase transition, generating new states with drastically different optical and electronic properties. While this has not been observed in the most actively investigated semiconducting transition metal dichalcogenides, 2H-MoS2 and 2H-WSe2, we found strain-induced structural phase transitions to take place in 1T-ZrS2 and 1T-ZrSe2, which possess optical and electronic properties similar to those of Mo- and W- compounds, but have different crystalline structure and orbital character. Our high-pressure Raman scattering, X-ray diffraction and optical absorption experiments revealed a reversible metallization of 1T-ZrSe2 at 8 GPa and an irreversible transformation of 1T-ZrS2 to a new semiconducting phase at 3 GPa, with smaller band gap by 1 eV (from 1.7 eV to 0.7 eV), a change that is optically evident. The study is complemented by structural investigation under pressure and ab initio band structure calculations. |
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H71.00209: WITHDRAWN ABSTRACT
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H71.00210: Electrostatically control interfacial states for stackable electronics Chen Po-Han, Yu-Ting Lin, Chun-An Chen, Yi-Cheng Chiang, I-Tung Chen, Yi-Hsien Lee Semiconducting monolayer of transition metal dichalcogenides (TMD) is ideal fundamental unit for stackable electronics because of its excellent optoelectronic properties. However, further applications are hindered with various issues from trap states of the monolayers. Here we develop a method to effectively engineer trap states of the monolayer MoS2 for excellent optoelectronic performances, including ultrahigh photoresponsivity (R) of 102~104 A/W, high sensitivity (D*) of 1011~1012 Jones and large absorbance. A scalable image sensor array of CVD-grown MoS2 monolayer is demonstrated. |
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H71.00211: Large-Scale Synthesis of MoS2 One-dimensional Nanostructures and Precision Manipulation Yun Huang, Zexi Liang, Kang Yu, Paulo Ferreira, Donglei (Emma) Fan In the family of two dimensional (2D) materials, molybdenum disulfide (MoS2) has received immerse attention. Herein, we report a scalable approach to synthesize MoS2 nanoribbons with controlled dimensions. Characterizations confirm the chemistry, morphology, and crystalline structures of materials obtained at different reaction stages, including MoO3, MoS2/MoO2 hybrid, and MoS2 nanoribbons. With the electric tweezers based on combined AC and DC electric fields, the MoS2 nanoribbons can be readily manipulated with desired orientations along arbitrary trajectories, e.g. along a cat drawing. Moreover, it is found that the electromechanical behaviors of the particles obtained at different growth stages strongly correlate with their electric properties, the demonstration of which could be utilized to monitor and understand the synthetic process of targeted nanomaterials. This work may lead to a new paradigm in the large-scale fabrication of 2D materials with designed dimensions and inspire their innovative applications in nanorobotics, micro/nanoelectromechanical system devices (MEMS/NEMS), as well as molecule delivery and release. |
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H71.00212: First Principles Electronic and Lattice Dynamics Calculations of TiSe2 and TiTe2 Warda Rahim, Philip King, David Scanlon TiSe2 bulk and monolayer both undergo a charge density wave (CDW) instability,1,2 whereas only monolayer TiTe2 undergoes a CDW transition.3 We performed electronic structure and lattice dynamics calculations (Phonopy code)4 for both of these Ti(IV) dichalcogenides using hybrid (HSE06)5 density functional theory. We also mapped the potential energy surfaces6 spanned by the imaginary mode eigenvectors to estimate the barrier associated with the transition and to track the route to the CDW phase. Our results successfully show that though TiTe2 bulk has no lattice instability, its monolayer has an instability similar to, but much weaker than that seen in TiSe2, highlighting the origin of a weak coupling CDW distortion brought about by a lattice instability. These results could have impact in understanding of CDW instabilities in other systems, particularly the methodology of following imaginary modes to track the transitions between phases. |
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H71.00213: Controlling the stereospecific bonding motif of Au-thiolate links and assessment of their catalytic properties Mohammed Sabri G. Mohammed, Luciano Colazzo, Aurelio Gallardo, Zakaria M Abd El-Fattah, José A. Pomposo, Pavel Jelínek, Dimas García de Oteyza Organosulfur compounds at the interface of noble metals have long been proved to be extremely versatile systems. In this work we explore the formation of gold-thiolate-based organometallic structures from 1,4-bis(4-mercaptophenyl) benzene (BMB) deposited onto Au(111) surface. By controlling the on-surface reaction conditions we can selectively choose the resulting structures to be either arrays of cyclic Au3BMB3 units or linearly stacked nanowires, although the former turn out to be the thermodynamically favored products[1]. Most interestingly, co-deposition of alkyne-functionalized pyrene derivatives on this system reveals the catalytic activity of the R-S-Au-S-R vertices on alkyne coupling reactions. |
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H71.00214: Optimal U values for 3d transition metal oxides within a SCAN+U framework Sai Gautam Gopalakrishnan, Olivia Long, Emily Carter Redox-active transition metal oxides that can tolerate oxygen off-stoichiometry are crucial ingredients for generating renewable fuels via oxide-based solar thermochemical reactors. However, any predictive modeling, such as using density functional theory (DFT) calculations, needs to accurately describe the energetics of redox reactions involving transition metals, if new candidates are to be found. Recently, we found that the strongly constrained and appropriately normed (SCAN) exchange-correlation functional requires a Hubbard U correction (determined, e.g., from experimental oxidation enthalpies) to accurately describe the ground state structure, magnetic moments, and electronic properties of Ce-, Mn-, and Fe-based systems. In the present work, we extend our approach to identify optimal U values for other 3d oxides within the SCAN+U framework. Although the absolute magnitude of U values required for all 3d metals is lower than what is needed using a generalized gradient approximation+U or a local density approximation+U approach, we find that the addition of U makes non-negligible improvements in ground state property predictions, particularly for Ti, V, Co, and Ni oxides, highlighting the importance of using a SCAN+U framework. |
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H71.00215: Polarization dependence photoluminescence in flexible two-dimensional MoS2 for lattice deformation characterization Yangbowen Liu, Xian Zhang Since Nobel Physics Prize in 2010 about graphene, intense research endeavors have been paid worldwide to comprehend the intrinsic characteristics of two-dimensional (2D) materials and explore their cutting-edge applications in bioengineering, energy storage and conversion, and nanoelectronics. 2D heterostructures consisting of various 2D materials are receiving extensive interests nowadays. However, there is a lattice deformation when different 2D materials are stacked together. Characterization of each 2D layer’s lattice deformation facilitates with the optimized 2D device design. In this project, we study the rotation angle dependent photoluminescence (PL) of one atomic layer of 2D MoS2 under a serious of external mechanical deformations. The PL shows a dependence with the sample rotation angle at stretched status. The intensities of two PL peaks (627 nm and 679 nm) have strong angle dependence and a serious of mechanical deformations (up to 10%) are performed. This research result can be used to accurately identify the value of lattice deformation in 2D heterostructures. |
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H71.00216: Optical measurements on phosphorus polymorphs. Carlos Josafat Cordero Silis, Elizabeth Chavira, Thomas Stegmann, Adriana Tejeda Cruz, Karla Eriseth Reyes Morales, Miguel Ángel Canseco Martínez The anisotropic electronic structure of phosphorene makes it promising, for research and technological applications. Its polymorphs are White Phosphorus, which transforms into Red or Violet at 280 °C and 550 °C, and Black Phosphorus obtained from White applying pressure (12000 Bar) or trough catalysis. This research focuses on alternative synthesis methods for these, given their prohibitive cost, using common available materials. |
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H71.00217: In-situ measurement of strain evolution in 2D materials on flexible substrates using Raman spectroscopy. Marc Mezzacappa, Henry Wright, Dheyaa Alameri, Mary Conley, Chi Hou Lei, Irma Kuljanishvili Since its recent discovery, extensive research investigating the physical properties of Graphene and other similar two-dimensional (2D) materials has been performed. Graphene’s excellent mechanical properties, flexibility, and optical transparency make it a promising candidate for a variety of layered architectures and hybrid devices. A custom low profile testing device was designed and manufactured in-house for in-situ physical measurements of single and multilayer 2D materials on flexible substrates using Raman spectroscopy. The design of the device allows for accurate and consistent strain application of both uniaxial bending and uniaxial tension in 2D materials. Here we use the device to investigate bending induced strain evolution in 2D materials through observation of characteristic Raman spectra band shifts. 2D materials used here were prepared via chemical vapor deposition (CVD) and were transferred to the flexible substrates. Our results provide information on strain development, substrate interaction, and adhesion properties of the 2D material tested. |
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H71.00218: Study of Low Energy Electron Transparency of Graphene and Doped-Graphene via
Electron Energy Analyzer Merid Belayneh Merid Legesse,1 Vineet Mohanty,2 Mohamed Farhat, Brian |
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H71.00219: Structural, electronic, and optical properties of defect-containing MX2 monolayers from first principles Jaron Kropp, Can Ataca In this work, we investigate the role of defects on the modification of the structural, electronic, and optical properties of transition metal dichalcogenide (MX2: M=Mo,W; X=S,Se) nanosheets. Using the cluster expansion formalism and density functional theory (DFT), we calculate the energetics and magnetic ordering of MX2 monolayers with various concentrations of chalcogen vacancies. The energetically favorable structures with desired vacancy concentration are then investigated further to determine the effects on the electronic, magnetic, and optical properties including the exciton binding energies. The structures we obtained from cluster expansion are then used as training sets for our machine learning algorithm to predict large scale MX2 monolayers with desired vacancy concentration. We employ classical molecular dynamic simulations to study in the effect of vacancy defect concentration on the structural deformation of freestanding MX2 nanosheets and nanoribbons. We report that after certain vacancy concentration values, MX2 monolayers deform from planar structures to buckled structures. This work not only provides insight into realistic (i.e. CVD grown) MX2 monolayers, but also provides guidance for defect engineering for device applications of MX2 structures. |
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H71.00220: Superconductivity in layered misfit chalcogenide BiSe-NbSe2 Kaya Kobayashi, Masaharu Shirata, Jun Akimitsu Layered misfit chalcogenides, (BiSe)1+d(NbSe2) is an anisotropic superconductor (Tc=2.3 K)[1]. The superconductivity is mostly carried out in NbSe2 layers, i.e. a superconducting NbSe2 layer is sandwiched by insulating BiSe layers. The situation for NbSe2 resembles the monolayer on a substrate, albeit the slight charge transfer is discussed from BiSe layers. We report the new structure of the series of the material, (BiSe)1+d(NbSe2)n, and the enhancement of Tc as the number of NbSe2 layers (n) increases. |
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H71.00221: Piezoelectric domain walls in van der Waals ferroelectric CuInP2Se6 Andrius Dziaugys, John A Brehm, Alex A Puretzky, Tianli Feng, Sabine M. Neumayer, Eugene Eliseev, Juras Banys, Yulian Vysochanskii, Michael McGuire, Sergei V. Kalinin, Sokrates T Pantelides, Nina Balke, Anna Morozovska, Petro Maksymovych Van der Waals layered chalcogenophosphates, such as CuInP2S6 and AgInP2S6, exhibit intriguing polar properties such as room temperature ferrielectric ordering, negative electrostriction, large elastic nonlinearity, proximity to ionic conductivity and multi-well ferroelectric potential, presumably due to a unique influence of the van der Waals gap. Here we will discuss anomalous properties of domain walls in ferrielectric selenophosphate CuInP2Se6 detected using piezoresponse force microscopy. Whereas in ferroelectrics, including a structurally similar case of ferrielectric CuInP2S6, electromechanical response and polarization vanish at the domain wall, the reverse is true in the case of CuInP2Se6, so that piezoresponse vanishes everywhere but the domain wall. And yet, these domain walls can be manipulated by electric field. We propose the existence of an antiferroelectric phase in the near-surface layer of CuInP2Se6, with locally enhanced polarization at antiferroelectric domain walls. Nature Comms. in review (2019). |
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H71.00222: Synthesis of Semiconducting Graphene Nanoribbons via Chemical Vapor Deposition Robert Jacobberger, Austin J Way, Vivek Saraswat, Michael Arnold Graphene nanoribbons (GNRs) are predicted to exhibit excellent charge and thermal transport, novel magnetic and spin-polarized edge states, and technologically useful bandgaps, provided that their edge structure and width are controlled with nearly atomic precision. However, producing GNRs with such a high degree of structural fidelity has been a major challenge. We have discovered a scalable technique to synthesize GNRs via the highly anisotropic crystal growth of graphene on Ge(001) during chemical vapor deposition. By tailoring the growth conditions, GNRs with nearly atomically-smooth armchair edges, tunable sub-10 nm widths, and lengths of hundreds of nanometers are synthesized. The GNRs are semiconducting with sizeable bandgaps and display high-performance charge transport at room temperature. By initiating growth from nanoscale seeds, arrays of GNRs with controlled placement and alignment are produced. GNRs are also grown on Si substrates by utilizing epitaxial Ge interlayers. This bottom-up method may provide a route for realizing state-of-the-art technologies based on semiconducting graphene. |
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H71.00223: A Novel Opto-mechanical method for Large-scale Production of Boron Nitride Nanosheets in Water Gayathri H N, Jyoti Shakya, Phanindra Sai, Arindam Ghosh Hexagonal boron nitride (h-BN) is considered as most promising material for next generation microelectronic and other technologies. It can be easily integrated with other 2D materials such as graphene and molybdenum disulfide (MoS2). The boron nitride nanosheet (BNNs) has lattice constant like that of graphene and a large electrical band gap. Also, it has an atomically smooth surface and large optical phonon modes. These qualities make it applicable as a substrate material for a high-performance graphene electronics and as an ideal nano filler in polymers for many application in polymer industry. To realize such applications at industrial level, the obvious task is to synthesize nanosheets in large scale. Here in we report synthesis of high quality BNNs in large quantities by a novel opto-mechanical method using water as a solvent, without adding any chemical or surfactants. The exfoliated BNNs have been extensively analysed for nanosheet area and thickness by SEM, AFM and Raman spectroscopy. |
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H71.00224: Mechanical and electrical properties of Ti3C2Tx MXene single flakes Alexey Lipatov, Mohamed Alhabeb, Haidong Lu, Babak Anasori, Alexei Gruverman, Yury Gogotsi, Alexander Sinitskii Two-dimensional transition metal carbides and nitrides, known as MXenes, are a large class of materials that are finding numerous applications ranging from energy storage and electromagnetic interference shielding to water purification and antibacterial coatings. While bulk applications of MXenes are rapidly developing, their intrinsic physical property characterization through single-flake measurements remains a largely unexplored area of research. Here, we report the elastic properties of monolayers and bilayers of the most important MXene material to date, Ti3C2Tx (T stands for surface termination) measured using nanoindentation with the tip of an atomic force microscope. The effective Young’s modulus of a single layer of Ti3C2Tx was found to be 0.33 ± 0.03 TPa, which is the highest among the reported values for solution-processed 2D materials, including graphene oxide. Individual Ti3C2Tx flakes also exhibit a high conductivity of 4600±1100 S/cm and field-effect electron mobility of 2.6±0.7 cm2/Vs. We found that the resistivity of individual flakes is only one order of magnitude lower than the resistivity of multilayer Ti3C2Tx films, which indicates a surprisingly good electron transport through the surface terminations of different flakes, unlike in many other 2D materials. |
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H71.00225: Two relaxation rates in the in-plane THz conductivity of a clean Sr2RuO4 thin film Youcheng Wang, Hari Nair, Nathaniel Schreiber, Jacob Ruf, Ludi Miao, Darrell Schlom, Kyle M Shen, Peter Armitage Understanding the metallic normal state of Sr2RuO4 could help solve puzzles about its unconventional superconducting state. The normal state of Sr2RuO4 is considered a clean Fermi liquid in the low temperature and low frequency limit. Herein we present time domain THz measurements of the optical conductivity of a highly clean, RRR (residual resistivity ratio) ≈ 53 epitaxial thin film, in which we find deviation from Fermi liquid scaling of a simple metal below 3 meV. The complex conductivity can be modeled with two Drude terms, the decay rate of both of which follows T^2 dependence. We discuss the physical implications of two conducting channels. We compare the results with our experiments on other metallic ruthenates including SrRuO3 and CaRuO3 with similar RRR. |
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H71.00226: Synthesis of 2D materials by direct heating of bulk sources Davoud Hejazi, Renda Tan, Swastik Kar Synthesis of high-quality 2D materials usually requires reactors/furnaces of various levels of complexities. A simple method of growing 2D materials or their combined structures (heterostructure, alloys etc.) that is easy to set up and run can accelerate 2D research. We find that single and multilayered 2D materials of various types can be easily fabricated by direct thermal evaporation. This is in stark contrast with conventional vapor-phase techniques that require chemical reactions of precursors and flow of an inert carrier gas so, substantially reducing the cost and complexities. Sources of target nanomaterials are taken in commercial bulk form, reduced to powder, placed on a clean container in close proximity of target substrate in an inert atmosphere, then heated to and held at a range of material-specific high temperatures and durations. The nanomaterials evaporate and deposit directly on the substrate in the form of well-formed crystals. The synthesis methodology is much simpler than the other methods (CVD, MBE, etc.). We present detailed analysis (AFM, optical images, Raman, photoluminescence) of various types of 2D materials/structures possible via direct, mixed, and sequential evaporation of bulk powders. |
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H71.00227: WITHDRAWN ABSTRACT
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H71.00228: Structural and Physical Properties of “Field-Edited” Iridates Gang Cao, Hengdi Zhao, Bing Hu, Nick Pellatz, Yu Zhang, Dmitry Reznik A great deal of theoretical work addressing exotic states for iridates has thus far met very limited experimental confirmation. The conspicuous discrepancies are due chiefly to the extreme susceptibility to structural distortions inherent in these materials. To fundamentally address this challenge, we have structurally “edited” these materials (borrowing the phrase “genome editing”) via application of magnetic field during single-crystal growth. Our results have demonstrated that the “field-edited” single crystals not only are much less distorted but also exhibit some long-sought phenomena absent in the same materials grown without a magnetic field. We present and discuss these results along with comparisons drawn from other relevant systems. |
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H71.00229: Electronic transport in graphene/RuCl3 heterostructures Sara Qubbaj, Everardo Molina, Vikram Nagarajan, Gilbert Lopez, Nicholas Breznay, Robert Kealhofer, Isaac Arriaga, Derek Bergner, James Analytis, Claudia Ojeda-Aristizabal Ruthenium Chloride (RuCl3), a spin-orbit assisted Mott insulator, presents exciting physics thanks to spin-orbit entangled moments with interactions that are highly anisotropic, making it a close realization to the Heisenberg-Kitaev model. RuCl3’s highly insulating character limits the accessible experimental techniques to those requiring bulk crystals, such as resonant magnetic scattering, magnetic susceptibility or heat capacity measurements. Here, we design and measure devices that implement few layers of RuCl3 into an electronic device to form a Gr/RuCl3 Van der Waals heterostructure (similar to heterostructures reported recently [1]) with the aim of studying in a quantum coherent regime, signatures of proximity effects between graphene and RuCl3’s magnetic ordered state at low temperatures. |
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H71.00230: Qualitative Description of Magnetoelectric Coupling in Multiferroic BTO/CFO Janus Fibers Saba Arash, Bryan Chavez, Matthew Bauer, Jennifer Andrew, Thomas M Crawford, Yanwen Wu The magnetoelectric coupling dynamics in multi-phase multiferroic materials was investigated in a perovskite-spinel fiber system with Janus structure consisting of ferroelectric barium titanate (BTO) and ferrimagnetic cobalt ferrite (CFO). We observed strong evidence of such coupling from the distinct changes in the second harmonic generation signals under different applied magnetic field orientations. Here, we provide a clear qualitative description of how the electrical polarization of the BTO half is affected by the changes incurred in the magnetization of the CFO half in different groups of fibers. We observed that although the results vary for different fiber ensembles due to the memory of the initial system, the subsequent changes in the fiber system correlate qualitatively and can be understood in a systematic way with our simple dipole model. |
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H71.00231: Strain-based magneto-electric coupling effect induced orbital reconstruction and near room temperature ferromagnetic insulator state in PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 heterostructure Chao Liu Multiferroic heterostructures attracts much attention due to fascinating potential applications in electric field control of magnetism and abundant physics significance. However, more and more fascinating phenomenon appearing near ferromagnetic/ferroelectric interface requires deeper investigation on this interface and the related coupling mechanism. Here, a near room temperature ferromagnetic insulator state in PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 heterostructures was reported by varying PbZr0.52Ti0.48O3 thickness. Abnormal enlarged c/a ratio in La0.67Sr0.33MnO3 by strain-based coupling effects, which lead to d3z2-r2 orbital preferable occupancy and narrower eg bandwidth, was regarded as the dominant reason while valence change induced by charge-based coupling effects could be limited responsible considering short screening length. This work paves a deeper understanding of strain-based coupling effects across ferromagnetic/ferroelectric interface and enrich physics content in La1-xSrxMnO3 based electron strong correlated system |
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H71.00232: Tunneling Transport in Gapped Graphene through a Bias-Tunable Potential Barrier Danhong Huang, Farhana Anwar, Andrii Iurov, Godfrey Gumbs, Ashwani Sharma We have investigated electron tunneling and transport properties for graphene through a non-square barrier with a finite slop in the potential profile. We have developed a new methodology based on thefinite-difference solution of the scattering equations for a Dirac electron, and have also built a perturbation theory for the electron transmission for the case with a small slope. Both gapped and gapless graphene materials have been considered in our calculations. All these predicted properties are expected to have the highest importance for novel electronic and optical devices. |
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H71.00233: Gauging electronic transport in Sodium Iridate and Vanadium Triiodide thin crystals through graphene heterostructures Everardo Molina, Sara Qubbaj, Vikram Nagarajan, Tai Kong, Gilbert Lopez, Nicholas Breznay, Robert Kealhofer, Derek Bergner, Isaac Arriaga, Robert J. Cava, James Analytis, Claudia Ojeda-Aristizabal Sodium Iridate (Na2IrO3) presents exciting ground states thanks to the combination of electronic correlations, spin-orbit coupling, crystal field effects and a honeycomb arrangement of the iridium ions. Vandium triiodide (VI3) on the other hand, constitutes a promising candidate for 2-D magnetism. Due to the highly insulating behavior of these materials, little progress has been made in terms of transport measurements. Here we explore an indirect transport measurement of thin exfoliated Na2IrO3 and VI3 crystals through a graphene heterostructure. |
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H71.00234: Asymmetry strain induced superdomain structures in (101)-oriented Pb(Zr0.2Ti0.8)O3 and PbTiO3 Sheng-Zhu Ho, Meng-Xun Xie, Yu-Chen Liu, Yu-Huai Li, Jan-Chi Yang, Yi-Chun Chen Ferroelectric materials in room temperature have attracted great scientific and technological interests due to its huge potential for applications in nonvolatile memory devices. Lead zirconate titanate (Pb(ZrxTi1-x)O3, PZT) compounds, with remarkable ferroelectricity, is one of the most commonly studied system. Abundant previous researches have shown that ferroelectric domain structures of the PZT system would depend on the orientation of epitaxial substrate due to the stain effect. In this study, we investigated the domain structures of (101)-orientated tetragonal Pb(Zr0.2Ti0.8)O3 (PZT) and PbTiO3 (PTO) epitaxial films grown on cubic SrTiO3 (110) substrates by vector piezoresponse force microscopy (vector-PFM). Interestingly, we observe superdomains with particular spontaneous polarizations on both PZT and PTO films which are under asymmetry strains from the substrate. However, comparing with those of (101)-orientated PTO, (101)-orientated PZT has more fine structures within one superdomain perioid, which are with polarization rotations along phi-direction observed by vector-PFM. As the result, we could further confirm the istrain effect break the in-plane symmetry of the PZT and PTO films and and lead to the superdomain structures. |
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H71.00235: Study of structural, electromagnetic and magnetoelectric properties of multiferroic composites Bablu Chandra Das, Md. Feroz Alam Khan, M. A. Matin, A.K.M. Akther Hossain Abstract |
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H71.00236: Thermally Induced Metastable Inter-Ferroelectric Phase Switching in Mechanically Biased Single Crystal Relaxor Ferroelectrics Peter Finkel, Stephan M Young, Samuel E Lofland, Margo Staruch In this work we examine a thermally induced metastable phase transition in mechanically biased piezoelectric [Pb(In1/2Nb1/2)O3]0.24[Pb(Mg1/3Nb2/3)O3]0.46[PbTiO3]0.32 domain-engineered single crystals. Our results show a purely thermally-driven first order ferroelectric rhombohedral-to-orthorhombic phase transition accompanied by a large, sharp discontinuity in strain while the piezocrystal is held under mechanical compressive bias stress and variable electric field bias. We demonstrate this transition can be cycled repeatedly with a small thermal hysteresis (< 3°C) under zero applied electric field with dynamic reversible strain jump of ~ 0.25 %. Moreover, we show that the thermally driven phase switching behavior can be tuned by varying the bias stress and/or electric field, illustrating the path for establishing effective control parameters and conditions for potential future applications such as actuators, thermoelectric transducers and sensors. |
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H71.00237: Colossal Dielectric Constant Achieved via Acceptor-Donor doped ZnO Ceramic Dong Huang, Chi-Chung Ling Materials having colossal dielectric constant (CDC) and low loss (, ) with good frequency stability is crucial for device miniaturization and high-energy density storage application. Hu et alrecently reported a temperature and frequency independent CDC with a low dielectric loss in acceptor-donor co-doped TiO2. The CDC is postulated to be originated from electron-pinned defect dipoles which is the acceptor-donor defect complex, though the detail mechanism and experimental evidence are lacking. |
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H71.00238: WITHDRAWN ABSTRACT
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H71.00239: The Effect of Semiconductor Nanostructures on the Performance of Nanometer-Thick Parallel Plate Capacitors Masoud Kaveh, Nikolas Roeske, Fazel Baniasadi, Chenggang Tao, Hoe Tan, Mykhaylo Lysevych, Chennupati Jagadish We fabricate nanometer thick, parallel plate capacitors which have semiconductor nanostructures as their dielectric spacers and investigate their capacitance as a function of geometry and the type and thickness of spacer and metal plates. Selected semiconductors are SrTiO3 nano-powder and GaAs and Si nanowires (NW) which have relatively high dielectric constants. 30 nm and 60 nm thick Au plates are fabricated on both solid glass and flexible poly (methyl methacrylate) substrate using an electron beam deposition system. The vertically aligned 50 nm diameter GaAs NWs were grown using the Au catalyzed vapor-liquid-solid method. The Si NWs are randomly oriented with an average diameter of 70 nm. The SrTiO3 nano-particles are cubical with a width of around 30 nm. The reference sample, Au plates with air as dielectric, reveal capacitance in the pico-Farad order. However, capacitor structures with semiconductor dielectrics show an enhancement of the total capacitance, mainly explained by the semiconductor spacer weakening the effective internal electric field. Photoluminescence measurements on the semiconductors adjacent to Au plates also show an energy transfer from semiconductor excitons to plasmon oscillations in the Au plates. |
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H71.00240: Pretransitional Diffuse Neutron Scattering in Ferroelectric KTa1-xNbxO3 Grace Yong, Ross Erwin, Oleksiy Svitelskiy, Jean Toulouse, Lynn A Boatner, Stephen M Shapiro Pretransitional diffuse neutron scattering in ferroelectric KTa1-xNbxO3 occurs at (110), (111), and (130) with no diffuse scattering at (100), and (200). These observations will be discussed using the elastic structure factor and `uniform phase shift' description. |
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H71.00241: The strong nonlinearity optical calculation of 3D Dirac semimetals. Tianning Zhang, Yee Sin Ang The optical nonlinearity of novel Dirac materials, such as graphene, have been extensively studied theoretically and experimentally in recent years. Due to the exceptionally strong light-matter interactions, Dirac material is promising in revolutionizing the functionality of photonic and optoelectronic device technology. In this work, we study the nonlinear optical response generated by the massless Dirac quasiparticles residing around the topologically-protected Dirac nodal points in three-dimensional (3D) Dirac topological semimetals in the terahertz frequency regime. Analytical expressions of third-order interband nonlinear optical conductivities are obtained based on semiclassical Boltzmann equation and quantum mechanical Floquet theory. Using Cd3As2 as an example, we demonstrate that the optical nonlinearity of 3D Dirac semimetal at terahertz frequency is comparable to that of the two-dimensional Dirac fermions in graphene. Importantly, the additional degree of freedom of 3D Dirac semimetal shall offer additional optical device design flexibility not found in atomically-thin graphene. |
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H71.00242: "Origin of Exceptional Magneto-resistance in Weyl Semimetal TaSb2" Pawan Kumar, Sudesh Sudesh, GANESH GURJAR, Satyabrata Patnaik We study magneto-transport properties in single crystals of TaSb2, which is a topological semimetal. In the presence of magnetic field, the electrical resistivity shows onset of insulating behaviour followed by a plateau at low temperature. Such resistivity saturation is generally assigned to topological surface states but we find that aspects of extremely large magneto resistance and resistivity plateau are well accounted by classical Kohler’s scaling. In addition, magneto-resistance in TaSb2 shows non-saturating field dependence. Evidence for anomalous Chiral transport is provided with observation of negative longitudinal magneto-resistance. Shubnikov-de Haas oscillation data reveal two dominating frequencies, 201 T and 455 T. At low temperature, the field dependence of Hall resistivity shows non-linear behaviour that indicates the presence of two types of charge carriers in consonance with reported electronic band structure. Analysis of Hall resistivity implies extremely high electron mobility. |
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H71.00243: Ultrahigh conductivity in Weyl semimetal NbAs nanobelts Cheng Zhang, Xiangyu Cao, Faxian Xiu In two-dimensional (2D) systems, high mobility is typically achieved in low-carrier-density semiconductors and semimetals. Here, we discover that the nanobelts of Weyl semimetal NbAs maintain a high mobility even in the presence of a high sheet carrier density. We develop a growth scheme to synthesize single crystalline NbAs nanobelts with tunable Fermi levels. Owing to a large surface-to-bulk ratio, we argue that a 2D surface state gives rise to the high sheet carrier density, even though the bulk Fermi level is located near the Weyl nodes. A surface sheet conductance up to 5–100 S per is realized, exceeding that of conventional 2D electron gases, quasi-2D metal films, and topological insulator surface states. Corroborated by theory, we attribute the origin of the ultrahigh conductance to the disorder-tolerant Fermi arcs. The evidenced low-dissipation property of Fermi arcs has implications for both fundamental study and potential electronic applications. |
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H71.00244: Suppression of magnetism and Seebeck effect in Na0.875CoO2 induced by SbCo dopants Mohammed H. N. Assadi, Marco Fronzi, Paolo Mele We examined the electronic properties of Sb-doped Na0.785CoO2 using density functional calculations based on GGA+U formalism. We demonstrated that Sb dopants were the most stable when replacing Co ions within the complex Na0.875CoO2 lattice structure. We also showed that the SbCo dopants adopted the +5 oxidation introducing two electrons into the host Na0.875CoO2 compound. The newly introduced electrons recombined with holes that were borne on Co4+ sites that had been created by sodium vacancies. The elimination of Co4+ species, in turn, rendered Na0.875(Co0.9375Sb0.0625)O2 non-magnetic and diminished compound’s thermoelectric effect. Furthermore, The SbCo dopants tended to aggregate with the Na vacancies keeping a minimum distance. Conclusions drawn here can be generalized to other highly oxidized dopants in NaxCoO2 that replace a Co. |
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H71.00245: Temperature influence in the broadening parameter of photoreflectance spectras on GaAs doped with Ge and Sn as aged samples Samuel Zambrano, Gerardo Fonthal, Jose Sierra, John Prias Aged samples of GaAs doped with Ge and Sn growth by liquid phase epitaxy, show temperature influence in the broadening parameter of the photoreflectance spectras domined mainly by the photon-defects interactions. The samples were characterized via Raman spectroscopy, X-ray diffraction technique and scanning electron microscopy. The photoreflectance spectras were taken by varying temperatures from 20 to 300 K. Optical measurements suggest that increase temperature and increases broadening parameter, exhibiting changes in the photon-defects interactions, possibly attributed to increase in aging defects. |
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H71.00246: Investigation of the obscure spin state of Ti-doped CdSe John Dimuna, Tucker Boyett, Anant K Ramdas, Irek Miotkowski, Thomas Pekarek, Jason Haraldsen Using computational and experimental techniques, we examine the nature of the 2+ oxidation state of Ti-doped CdSe. Through stoichiometry and magnetization measurements, the weakly-doped material of Cd1-xTixSe (x = 0.0043) shows the presence of a robust spin-1 magnetic state of Ti, which is indicative of a 2+ oxidation state. Given the nature of the Ti2+ state, we investigate the electronic and magnetic states with density functional theory for a supercell of CdSe with an ultra-low concentration of Ti. We find that reproducing the magnetic moment of spin-1 requires an onsite potential of 4-6 eV must be included. Furthermore, the electronic structure and density of states show the presence of a Ti-d impurity band above the Fermi level and a weakly metallic state for a U = 0 eV. However, the evolution of the electronic properties as a function of the Hubbard U shows that the Ti-d drop below the Fermi around 4 eV with the onset of a semiconducting state. The impurity then mixes with the lower valence bands and produces the 2+ state for the Ti atom. |
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H71.00247: Understanding the spin-glass state through the magnetic properties of Mn-doped ZnTe Alexandria R Alcantara, Dina Matev, Anant K Ramdas, Irek Miotkowski, Thomas Pekarek, Jason Haraldsen To understand the spin-glass state of diluted magnetic semiconductors, we have examined the magnetic properties of Zn1-xMnxTe using density functional theory and magnetization measurements. Utilizing the generalized gradient approximation, we investigate the dependence of the Hubbard onsite potential on the magnetization and electronic structure. We find that the ground state magnetic preference is antiferromagnetic and that the onsite potential is needed to harden the magnetic moment of S = 5/2. Furthermore, the system is clearly semi-conducting, which suggests that the spin-glass nature of the compound is produced through the magnetic exchange interactions through the p- and d-orbital hybridization. |
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H71.00248: (Si)GeSn Semiconductors for integrated optoelectronics and quantum electronics Simone Assali, Aashish Kumar, Mahmoud Atalla, Salim Abdi, Samik Mukherjee, Anis Attiaoui, Oussama Moutanabbir Si-compatible photonic and opto-electronic devices operating at mid-infrared wavelengths can now be fabricated using Sn-containing group IV semiconductor (Si)GeSn alloys, directly grown on a Si substrate. The possibility to independently engineer strain and composition in this new class of semiconductors allows for a high degree of tunability of band structure and lattice parameter of the material, thus enabling a variety of multi-layer heterostructures and low-dimensional systems. |
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H71.00249: Long-lived modulation of plasmonic absorption by remote thermal injection John Tomko, Evan Runnerstrom, Yi-Siang Wang, Joshua Nolen, David Olson, Kyle Kelley, Angela Cleri, Josh Nordlander, Joshua D Caldwell, Oleg Prezhdo, Jon-Paul Maria, Patrick Hopkins Light interactions capable of inducing charge and energy transfer across interfaces are the fundamental basis for a multitude of technologies, including photocatalysis, energy harvesting, and photodetection. One of the more common mechanisms associated with these processes relies on injection of the charge carrier iteself. In this work, we elucidate upon a novel means of of electronic energy injection that can be accessed by relying on non-equilibrium dynamics achievable at metal-semiconductor interfaces that has yet to be realized. This remote thermal injection (RTI) process is demonstrated through an ultrafast pump-probe technique that relies on monitoring the optical properties of a mid-infrared epsilon-near-zero cavity following optical excitation of a remote contact, providing a highly sensitive probe into the spatial variations of electron density and energy relaxation mechanisms in the heterostructure. These results are further supported via ab initio density functional theory (DFT) simulations. |
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H71.00250: Investigation of Exciton-Phonon Coupling in Cesium Lead Bromide Perovskite Nanosheets with photoluminescence Xiangzhou Lao, Shijie Xu Variable-temperature photoluminescence (PL) spectra of cesium lead bromide (CsPbBr3) nanosheets were measured in a low temperature range of 5 to 40 K. In this interested low temperature range the measured PL spectra exhibit a main zero-phonon peak and its longitudinal-optical (LO) phonon sideband, and are quantitatively simulated using the multimode Brownian oscillator (MBO) model. Good agreement between theory and experiment enables us to determine several key parameters characterizing the exciton−phonon coupling, including the dimensionless Huang-Rhys factor S accounting for the exciton-LO phonon coupling strength and the damping constant γ for the phonon bath (quasi-continuous acoustic phonons) dissipation. It is found that Huang-Rhys factor S peculiarly tends to diminish upon increasing the temperature, suggesting weakened exciton-LO phonon coupling in the interested low-temperature range. However, as often observed in solids, the damping constant γ in the nanosheets increases almost linearly with the rise of temperature. This study may shed some light on the complex exciton-phonon scattering mechanisms in solids. |
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H71.00251: Carrier Multiplication in Quasi-1D Nanosystems: A Time-Dependent Density Functional Theory Study Junhyeok Bang Carrier multiplication (CM) is a fundamental process in the electronic excited state, which generates multi-excitons from a single-photon absorption. CM has been intensively investigated for photovoltaic applications, because it can improve optoelectronic devices efficiency. However, CM is rarely witnessed in conventional semiconductors, calling for an unconventional material enhancing the CM. Here, using real-time time-dependent density functional theory, we show that CM occurs in quasi-one-dimensional (1D) nanosystems derided from 2-dimensional van der Waals materials. The origin of CM in quasi-1D, i.e., releasing the constraints of the CM process, are different from that in 0D nanosystems, i.e., phonon bottleneck. The results provide the way to control the excited carrier dynamics and CM in nanosystems. |
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H71.00252: WITHDRAWN ABSTRACT
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H71.00253: Two-Exciton states in Cyanine Dimers on DNA Scaffolds Paul Cunningham, Sebastian A. Dias, Young C. Kim, Divita Mathur, Donald L Kellis, Bernard Yurke, Ryan D Pensack, William B Knowlton, Igor L. Medintz, Joseph S. Melinger The control of intermolecular coupling is a pathway towards achieving highly efficient energy transport in artificial light-harvesting networks. Similar requirements are also needed for the design of molecular wires and logic structures within the field of molecular excitonics. Here we report on the creation of cyanine dye homodimers on DNA scaffolds. The DNA provides a backbone to precisely control dye placement through covalent attachment and thereby the coupling strength, allowing the absorption and emission properties of the resulting dimers to be tailored. Through this strategy, we are able to realize delocalized one- and two-exciton states, the later of which is a first for a DNA-scaffolded system. Such multi-exciton states hold promise for entangled photon emission and molecular logic gates. Both the one- and two-exciton states are well described by molecular exciton theory when electron-vibrational coupling is accounted for. We also address the impact of molecular motion on the dynamics of these states, and identify a path towards greater control of these properties. |
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H71.00254: Exact Steady-state Solution of Electron Transport Through a Quantum System Coupled with Dissipative Electrodes Tse-Min Chiang, Liang-Yan Hsu In the framework of the Lindblad quantum master equation, we develop a theory which allows us to describe electron transport through a molecular junction coupled with dissipative electrodes. We generalize the theory of coherent quantum transport and include the electronic dissipation in electrodes. Moreover, we derive an exact solution of steady-state current and analyze the asymptotic behavior in the different limits of electronic dissipation. Furthermore, we obtain a Landauer-type formula and show that this formula can be reduced to the original Landauer formula in the condition of zero dissipation rate. |
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H71.00255: Magnitoexcitons in Monolayer Transition-Metal Dichalcogenides Anastasia Spiridonova Monolayer transition-metal dichalcogenides (TMDC) such as MoS2, MoSe2, WS2 and Se2 host a series of exciton Rydberg states denoted by the principal quantum number n = 1, 2, 3, etc. We study the 1s–2s exciton Rydberg states in TMDC monolayers encapsulated by hexagonal boron nitride (hBN) under the action of a magnetic field. The exciton Rydberg states exhibit similar Zeeman shifts but distinct diamagnetic shifts from each other. Excitons in the magnetic field are described in the framework of the potential model. We have used the Keldysh potential to calculate the energies of exciton Rydberg states in hBN-encapsulated monolayers of MoS2, MoSe2, WS2, and WSe2 under varying magnetic field. Our calculations use as inputs the effective masses of electron and hole obtained in the framework of the density functional theory. The binding energies of exciton are calculated using the first-order perturbation theory, which gives good approximation only in the low magnetic field. These binding energies are comparable to experimental measurements. Our results are consistent with the other theoretical predictions. |
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H71.00256: Hot-carrier generation in plasmonic nanoparticles: Atomic-scale analysis Tuomas Rossi, Paul Erhart, Mikael Kuisma Metal nanoparticles absorb light much more than their physical size would suggest due to the excitation of a localized surface plasmon resonance. After its excitation, the plasmon resonance decays into high-energy electrons and holes, which, combined with the large absorption cross section, make metal nanoparticles attractive hot-carrier generators for photocatalysis. In this presentation, we describe the femtosecond dynamics of localized surface plasmons in noble metal nanoparticles by using time-dependent density-functional theory (TDDFT). We track the plasmon formation and decay into hot carriers in terms of contributing electron-hole transitions [1,2]. By analyzing the resulting hot-carrier distributions down to atomic-scale detail, we shed light on the hot-carrier generation in catalytically-relevant edge and corner sites of nanoparticles [2]. |
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H71.00257: ABCs of strong exciton–plasmon coupling in 2D TMDCs Aaron Rose, Jeremy R. Dunklin, Lucy Metzroth, Hanyu Zhang, Elisa M Miller, Jao van de Lagemaat We present experimental details of strong exciton–plasmon coupling in 2D MoS2 at the A-, B-, and C-excitons at room temperature. In one experiment, we show plasmon-mediated coherent hybridization of the A- and B-excitons. Rabi splitting of ~70 meV in k-space at each exciton is also shown. The observation of coherent coupling between different exciton energy levels in a valley-polarized material suggests the possibility of valleytronic quantum information transport and/or spin entanglement. |
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H71.00258: Tunability of thermal conductivity in lead chalcogenide nanowire heterostrutures by strain or alloying Mack Adrian Dela Cruz, Nick Boecker, Gary Pennington
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H71.00259: Imaging Nematic Transitions in Iron-Pnictide Superconductors with a Quantum Gas Fan Yang, Stephen Taylor, Stephen D Edkins, Johanna Palmstrom, Ian Fisher, Benjamin L Lev The SQCRAMscope is a recently realized Scanning Quantum CRyogenic Atom Microscope that utilizes an atomic Bose-Einstein condensate to measure magnetic fields emanating from solid-state samples. Here, we combine the SQCRAMscope with an in situ microscope that measures optical birefringence near the surface of a sample to study iron-pnictide superconductors, where the relationship between electronic and structural symmetry-breaking resulting in a nematic phase is under debate. We conduct simultaneous and spatially resolved measurements of both bulk and surface manifestations of nematicity via transport and structural deformation channels, respectively. By performing the first local measurement of emergent resistivity anisotropy in iron pnictides, we observe a spatially inhomogeneous increase in the temperature at which optical birefringence appears near the surface over that at which anisotropic local transport appears within the bulk. This is consistent with the existence of a higher-temperature surface nematic transition, albeit one that emerges inhomogeneously. More broadly, these measurements demonstrate the SQCRAMscope's ability to reveal important insights into the physics of complex quantum materials. |
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H71.00260: Monte-Carlo simulations of a random-field Ising-O(3) model Nathaniel Page, Thomas Vojta Many of the iron-based superconducting compounds undergo a structural phase transition and stabilize a stripe-like spin-order at low temperatures. We investigate the relation between the structural and magnetic phase transitions in these materials and study the effects of random strain commonly found in the samples. |
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H71.00261: Abstract Withdrawn
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H71.00262: Specific Heat Study in Iron Based Superconductors: A Theoretical Three-Orbital Model Analysis. Madhavi Ahalawat, Ajay Singh The present work deals with the study of specific heat in superconducting state of iron based superconductors. In these materials, five 3d orbitals due to iron, Hund's coupling and electron correlations coexist and dominate electronic properties of these systems. Therefore, we have attempted the theoretical analysis based on three orbitals per site tight-binding model Hamiltonian containing hopping between orbitals, Hund's coupling and intra and inter orbital Coulomb interaction. We have employed Green's function technique within BCS mean field approximation to calculate the expresssions of superconducting energy gap parameter and quasiparticle energies and used these results to calculate specific heat jump as a function of temperature and various parameters of the model Hamoiltonian. Then we compared the results with the recent specific heat data and other relevant data of iron based superconductors. |
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H71.00263: Contribution of substrate phonon to the superconductivity of 1 unit-layer FeSe on SrTiO3 Hoyeon Jeon, Minjun Lee, Jin Mo Bok, Han-Yong Choi, Yunkyu Bang, Jungpil Seo, Jungseok Chae, Young Kuk A single unit-layer (1 UL) FeSe grown on SrTiO3 is one of Fe-based superconductors and has a high superconducting transition temperature compared to bulk FeSe of which Tc is near 8K. To investigate interface effect, especially phonons of substrate, we used scanning tunneling microscope (STM) and measured local electron density of states (DOS) of 1 UL FeSe on SrTiO3. Our results show that the spectral features depend on the phonon dispersions of FeSe as well as that of SrTiO3. Phonon density of states and electron-phonon coupling constant were calculated according to Eliashberg theory. |
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H71.00264: S+- Superconductivity in Electron-Doped Iron Selenide by Exchange of Hidden Spin Fluctuations Jose Rodriguez The observation of spin resonances around the corner of the unfolded Brillouin zone in intercalated iron-selenide high-Tc superconductors is consistent with the presence of low-energy hidden spin fluctuations in these materials. We develop an Eliashberg theory based on the exchange of hidden spin fluctuations by electrons in the principal 3dxz and 3dyz orbitals of the iron atom. At half filling, and in the absence of interactions, an electron-type Fermi surface exists at the center of the unfolded Brillouin zone and a hole-type Fermi surface exists at the corner of the unfolded Brillouin zone. As the interaction strength grows strong, Eliashberg theory predicts a Lifshitz transition to electron/hole Fermi surface pockets at the corner of the folded Brillouin zone. They are extremely faint because of wavefunction renormalization. The Eliashberg theory also predicts a rigid shift of the renormalized band structure upon electron doping, resulting in small but faint hole Fermi surface pockets, and in larger electron Fermi surface pockets. Last, the Eliashberg theory predicts an instability to S-wave Cooper pairing that alternates in sign between the electon-type and the hole-type Fermi surface pockets. |
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H71.00265: Giant enhancement of critical current density at high field in superconducting (Li,Fe)OHFeSe films by Mn doping Dong Li, Jie Yuan, Peipei shen, Chuangying Xi, Jinpeng Tian, Shunli Ni, Jingsong Zhang, Zhongxu Wei, Wei Hu, Zian Li, Li Yu, Jun Miao, Fang Zhou, Li Pi, Kui Jin, Xiaoli Dong, Zhongxian Zhao Critical current density (Jc) is one of the major limiting factors for high-field applications of iron-based superconductors. Here, we report that Mn ions are successfully incorporated into nontoxic superconducting (Li,Fe)OHFeSe films. Remarkably, the Jc is significantly enhanced from 0.03 to 0.32MA cm−2 under 33 T, and the vortex pinning force density monotonically increases up to 106 GN m−3, which is the highest record so far among all iron-based superconductors. Our results demonstrate that Mn incorporation is an effective method to optimize the performance of (Li,Fe)OHFeSe films, offering a promising candidate for high-field applications. |
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H71.00266: Results of Point-Contact Spectroscopy Measurements of the Energy Gap of Ph-doped
Iron Pnictides BaFe 2 (As 1-x P x ) 2 Brett Conti, Keeran O Ramanathan, Erik Cauley, Chenglin Zhang, Yu Song, Guotai Tan, Pengcheng Dai, Roberto Ramos The study of multi-band superconductivity has gained momentum over the past few years, especially |
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H71.00267: Quantum phase transition between the quantum anomalous Hall liquid and insulator states Chang Liu, Yunbo Ou, Yang FENG, Gaoyuan Jiang, Weixiong Wu, Shaorui Li, Zijia Cheng, Ke He, Xucun Ma, Qikun Xue, Yayu Wang The quantum anomalous Hall (QAH) effect has been discovered in magnetically doped topological insulator (TI) thin films in zero magnetic field. A fundamental question concerning the QAH effect is whether it is merely a zero-magnetic-field quantum Hall (QH) effect, or if it can host unique quantum phases and phase transitions that are unavailable elsewhere. Here we perform transport studies on more than 80 QAH samples with different level of disorders. We discover two novel quantum phases, namely the QAH liquid and anomalous Hall (AH) insulator, and the quantum phase transition between them driven by magnetic field. Surprisingly, a universal quantum resistance h/e2 is observed at the coercive field of QAH liquid samples in the low disorder limit. We propose that the transmission between chiral edge states, tunable by disorder and magnetic field, is the key for unraveling the peculiar quantum transport phenomena in magnetic TIs. |
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H71.00268: High throughput screening of magnetic thermoelectric materials based on anomalous Nernst effect by first-principles study Hikaru Sawahata, Naoya Yamaguchi, Susumu Minami, Fumiyuki Ishii The thermoelectric conversion based on the anomalous Nernst effect (ANE) has attracted attention because the ANE realizes the high-density integration more easily compared to that based on the Seebeck effect. This effect is induced by the anomalous Hall conductivity (AHC), and if the AHC changes drastically as a function of the Fermi level, we expect the large ANE [1]. In this study, we implemented the method of computing AHC in metallic systems efficiently [2] to OpenMX code, and we performed high-throughput screening, searching for two-dimensional ferromagnetic materials which have the large Nernst coefficient by the first-principles calculation. |
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H71.00269: The evolution of magnetism in intrinsic magnetic insulator material MnBi2Te4(Bi2Te3)n Fucong Fei Magnetic topological insulators (MTIs) are promising platforms for the observation of quantum anomalous Hall effect (QAHE), which is a long-expected dissipationless quantum transport phenomenon without applying external magnetic field. The recent progress on intrinsic MTI materials shed new light on the observation of higher temperature of QAHE. Here we grow the high-quality single crystals of three promising intrinsic MTI candidates MnBi2Te4(Bi2Te3)n (n = 0,1,2). By magnetic measurement, we discover that the all three compounds show anti-ferromagnetic (AFM) behavior, while the magnetic transition temperature decreases when increasing the value n. Meanwhile, by transport measurement, anomalous Hall effect can be observed in all three samples and the behaviors are correspondingly consistent with the magnetic measurements. The AFM coupling becomes weaker since the critical magnetic field for anti-ferromagnetism to ferromagnetism transition becomes lower when increasing n, and net ferromagnetic moment retains in n = 1 and 2 under low temperature. We believe that the tunable magnetic and transport properties by controlling the component ratio in MnBi2Te4(Bi2Te3)n provide an ideal platform to investigate the high-temperature QAH phase and the related physics. |
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H71.00270: Topological Electronic Structure and Its Temperature Evolution in Antiferromagnetic Topological Insulator MnBi2Te4 Yujie Chen, Lixuan Xu, Jiaheng Li, Yiwei Li, Hongyuan Wang, Chaofan Zhang, Hao Li, Yang Wu, Aiji Liang, Cheng Chen, Sungwon Jung, Cephise Cacho, Yuanhao Mao, Shuai Liu, Meixiao Wang, Yanfeng Guo, Yong Xu, Zhongkai Liu, Lexian Yang, Yulin Chen The intrinsic magnetic topological insulator MnBi2Te4 exhibits rich topological effects such as quantum anomalous Hall effect and axion electrodynamics. Here, by combining the use of synchrotron and laser light sources, we carry out comprehensive and high-resolution angle-resolved photoemission spectroscopy studies on MnBi2Te4 and clearly identify its topological electronic structure. In contrast to theoretical predictions and previous studies, we observe topological surface states with diminished gap forming a characteristic Dirac cone. We argue that the topological surface states are mediated by multidomains of different magnetization orientations. In addition, the temperature evolution of the energy bands clearly reveals their interplay with the magnetic phase transition by showing interesting differences between the bulk and surface states, respectively. The investigation of the detailed electronic structure of MnBi2Te4 and its temperature evolution provides important insight into not only the exotic properties of MnBi2Te4, but also the generic understanding of the interplay between magnetism and topological electronic structure in magnetic topological quantum materials. |
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H71.00271: Multifold Weyl nodes in a nonsymmorphic garnet compound Hyo-Sun Jin, Kwan-Woo Lee In condensed matters, now, many systems show linear band crossings of 4-fold Dirac nodes or 2-fold Weyl nodes, which have been sought for a long time in high energy physics. Recently, multi-fold nodes, which have no high energy counterpart, have been also proposed, e.g., 3-, 6-, and even 8-fold Weyl nodes. However, except triple-node points, no experimental realization has been successful yet. In this presentation, we will introduce an interesting real system with various exotic Weyl nodes, lying not far away from the Fermi energy. |
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H71.00272: Decoupling of electronic thermal conductivity and electrical conductivity in the magnetic nodal semimetal CeAlGe Fei Han, Quynh Nguyen, Thanh Nguyen, Ricardo Pablo Pedro, Anuj Apte, Nina Andrejevic, Mingda Li Wiedemann-Franz (WF) law is a robust empirical law stating that the ratio between the electronic thermal conductivity and electrical conductivity is related by a universal Lorenz number. For conventional materials, this law is strictly obeyed even when the electronic thermal conductivity and electrical conductivity are suppressed by magnetic fields. In the magnetic nodal semimetal CeAlGe, we observed a decoupling of electronic thermal conductivity and electrical conductivity. |
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H71.00273: Magneto-transport properties of antiferromagnetic Weyl semimetal CuMnSb VIPIN NAGPAL, Satyabrata Patnaik The electrical resistivity and magneto-transport properties of reported magnetic Weyl semimetal CuMnSb is studied. CuMnSb with an antiferromagnetic transition at 60K is synthesized using solid state reaction technique and crystallizes in cubic lattice structure with space group F-43m (216). No abrupt change in resistivity is observed below the transition under the application of 5T field. A highest non-saturating MR of 4% is observed at 5K and 6T. It is analyzed that MR in CuMnSb arises from the contribution of linear field B dependence as well as the parabolic B2 term. |
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H71.00274: Molecular beam epitaxy growth of (MnSb2Te4)(Sb2Te3)n SL/QL sequences Ido Levy, Haiming Deng, Steven Alsheimer, Lia Krusin-Elbaum, Maria C Tamargo Recent predicted intrinsic magnetic topological materials in the MB2T4-family (where M = V, Mn, Ni or Eu, B = Bi or Sb, T = Te, Se, or S) show a great promise for realizing intrinsic axion insulators and quantum anomalous Hall (QAH) insulators. These materials modify the B2T3 crystal structure forming septuple layers (SL) in the form of T-B-T-M-T-B-T. Not all of the listed magnetic TI candidates have been yet explored, and thus far out-of-plane surface magnetization was only found in MnBi2Te4 and MnSb2Te4. Both materials are antiferromagnetic (AFM) in the bulk and not suitable for QAH unless they have odd number of SLs. Recent studies in MnBi2Te4 have shown that separating SLs with Bi2Te3 quintuple layers (QL) turns an AFM into a ferromagnet (FM). Here we show that through layer-by-layer growth using molecular beam epitaxy (MBE) we can control the SL/QL sequence. We describe the conditions for which MnSb2Te4/Sb2Te3 sequence is ferromagnetic with Tc higher than that in the Bi-based SL/QL sequence, as witnessed by large anomalous Hall signal with coercive field ~0.1 T at 2 K. The structural (TEM and HR-XRD) characterization and the optimization of the SL/QL sequence will be presented. |
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H71.00275: First-principles theory of Cr-vacancy in BaZrO3 as a solid-state qubit candidate Jaewook Lee, Hosung Seo Recently, remarkable advances have been made in the development of solid-state quantum bits (qubits), which are the basic hardware units of quantum information processing. One of the leading solid-state qubit platforms is the nitrogen-vacancy (NV) center in diamond. Furthermore, a significant interest has been emerging in the literature to develop such defect-based qubits in diverse wide-gap semiconductors for broadening the scope of the solid-state quantum information. In this study, we explore a Cr-O vacancy complex in BaZrO3 as a potential solid-state qubit candidate. We use first-principles density functional theory to examine the stability and the electronic and spin properties of the Cr-O vacancy pair in BaZrO3. To investigate the stability of the defect in various charge states, we calculate the defect formation energy of Cr-vacancy in BaZrO3. In addition, we use HSE06 hybrid functionals to accurately calculate the defect level diagram and the zero-phonon line of the Cr-O vacancy. In the poster, we also discuss the recent progress and challenges in computational design of new defect qubits in complex wide-gap materials. |
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H71.00276: Magnetic-field and tunable-barrier effects on charge transport in DNA heterostructures Yong Joe, Alaa Alsaid, Ibtisam Abu Alkhayr The tunable barrier and magnetic field effects are studied in the electron transport of the double-stranded DNA molecular electronic structure. Our theoretical approach involves the application of the two-dimensional tight-binding Schrödinger equation to calculate transmission and electric current through the nearest-neighbors of twenty base-pairs’ DNA. A combination of G-C and A-T base-pairs of DNA, which can be considered as a barrier and a well, forms a superlattice in semiconductor heterostructures and exhibits a miniband whose width depends on the strength of the barriers and energy level of the wells. We also incorporate a variation of magnetic field flux density into the hopping integrals as a phase factor and observe Aharonov-Bohm (AB) oscillations in the transmission. It is shown that for non-zero magnetic flux, the transmission zero leaves the real-energy axis and moves up into the complex-energy plane. We also point out that both the hydrogen bonds between the base pair and the coupling between leads and DNA with flux variations play a role to determine the periodicity of AB oscillations in the transmission. |
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H71.00277: Non-Hermitian Thermal Emitters using Metal-Semiconductor Hybrid Resonators Chloe F Doiron, Gururaj Naik Thermal emitters always have absorption losses and hence are open systems. Open systems are non-Hermitian and are best described by non-Hermitian physics. Here, we develop a non-Hermitian description of resonant thermal emitters and thereby take advantage of absorption loss in the system. Further, the non-Hermitian description provides new design tools such as symmetry, phase, and topology to control the properties of the thermal emission. We demonstrate such a thermal emitter using coupled plasmonic and photonic resonators. A lossless silicon photonic resonator is coupled to a lossy tungsten plasmonic resonator via a spacer. As the spacer thickness is increased, the thermal emission from the device held at 1000 K exhibits a transition from PT-symmetric to symmetry-broken phase through an exceptional point. The thermal emission from the device breaks the trade-off between emission brightness and spectral selectivity and simultaneously achieves both. Further, we show that the internal phase of resonators is a powerful tool to control the thermal emission from this device. Overall, this work is an unorthodox approach towards designing not only thermal but also other nanophotonic light sources. |
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H71.00278: The effect of van der Waals force on two-dimensional SiC/GeC heterostructures Safia Abdullah R Alharbi, Ming Yu The effect of van der Waals interaction on two-dimensional (2D) SiC/GeC heterostructures has been studied based on the density functional theory. The van der Waals interaction is considered by employing the semi-empirical correction scheme of Grimme [1], which is used in optimizing the equilibrium interlayer distance and binding energy between 2D monolayers. We found that for the layered SiC/GeC heterostructure with the C-Ge (Si-C) species order, the cohesive energy as a function of interlayer distance is about 0.03 eV per unit cell lower than that with the C-C (Si-Ge) species order, for both AA and AB stacking. Further findings show that the interlayer electrostatic forces mainly stabilize the equilibrium distance for the C-Ge (Si-C) species ordering, and vdW interactions only make the system attain a lower cohesive energy. On the other hand, vdW forces stabilize the interlayer distance for the C-C (Si-Ge) species order. These preliminary results suggest that interlayer electrostatic forces may play a role in ionic-like multilayer heterostructures. |
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H71.00279: Experimental studies of nonlinear optics of self-assembled hyperbolic metamaterials Will Korzi, Jonathon Cartelli, Bryan Augstein, Kent Hess, Naveen Kadasala, Stephen Blama, Mary Sajini Devadas, Vera N Smolyaninova, Igor I Smolyaninov Sub-wavelength confinement of light in nonlinear hyperbolic metamaterials due to formation of spatial solitons has attracted much recent theoretical attention because of its seemingly counter-intuitive behavior. In order to achieve self-focusing in a hyperbolic wire medium, a nonlinear self-defocusing Kerr medium must be used as a dielectric host. It was demonstrated that this behavior finds natural explanation in terms of analogue gravity in effective “optical spacetime”, which can be used to describe nonlinear optics of a hyperbolic wire medium. In this work we will report first experimental observation of this effect using iron-cobalt ferrofluid-based self-assembled hyperbolic metamaterials subjected to external magnetic field. |
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H71.00280: Enhancing the Light Emission of Colloidal Quantum Dots with Dual-band Absorbers Based on Metasurfaces Dongfang Li, Chun-Chieh Chang, Ajay Singh, Jennifer A Hollingsworth, Hou-Tong Chen Quantum dots (QDs) are essential light emitters with great tunability of spectrum and find important technological applications in various areas, including light-emitting devices, photovoltaics, and bioimaging. The recent advance of metamaterials has enabled the direct control of the light emission properties with patterned ultrathin metallic films, ranging from enhanced light emission and modified fluorescence spectrum to well-defined polarization and unidirectional radiation. However, the outcoupling efficiency of two-dimensional (2D) QD-based optoelectronic devices is still limited. Here we propose and demonstrate the enhancement of the light emission of QD-based 2D optoelectronic devices at around telecom wavelengths by employing dual-band perfect absorbers based on plasmonic metasurfaces. The two resonant peaks of the absorber simultaneously match the absorption and radiation wavelengths of non-blinking “giant” QDs at the telecom regime, thus enhancing the excitation pump meanwhile maintaining the efficient outcoupling of the light emission. These findings will not only benefit technological applications of QD-based optoelectronic devices but also offer better understanding of the fundamental physical mechanisms of light-matter interactions. |
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H71.00281: High-Yield Production of Nanoplatelet Bi2Te3 via Supercritical Ball Milling in Carbon Dioxide Mohamed Atwa, Tessui Nakagawa, Makoto Schreiber, Yoshinori Okada Nanoplatelet Bi2Te3 is highly desired as a starting to powder for the consolidation of bulk nanostructured thermoelectric legs, as low-dimensional Bi2Te3 has long been expected to result in a higher Seebeck coefficient and lower thermal conductivity, leading to an unprecedented enhancement in the thermoelectric figure of merit (zT) in this material. The production of few-layer Bi2Te3 nanoplatelets has thus far mainly been limited to low-yield hydrothermal synthesis techniques. Studies have suggested that Bi2Te3 degrades in the presence of water, making such hydrothermal techniques inherently non-ideal for the production of high thermoelectric performance Bi2Te3 nanoplatelets. In this study, we show that gram-yield quantities of few-layer Bi2Te3 nanoplatelets are preferentially exfoliated along the basal plane using a novel, “all-dry” supercritical carbon dioxide (scCO2) ball milling technique. We will discuss advantages of our method in terms of the size, morphology, and crystallinity of the resulting nanoplatelets are compared against conventional ball milling techniques. |
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H71.00282: Tuning structural and electronic properties of α-Te tubular nanostructures by uniaxial strain Yanrong Guo, Jinjin Wang, Songyou Wang, Yu Jia, Wan-Sheng Su Tellurene, a new member of two-dimensional family materials, shows outstanding photoelectric characteristics. Here, a first-principles calculation is employed to explore the effect of uniaxial strains on the electronic properties for α-Te tubular nanostructures with various tube sizes. Under compressive and tensile strains of 10%, the atomic structures of α-Te tubular nanostructures have not been destroyed, demonstrating they have good flexibility. Interestingly, we found armchair (5,5) α-Te tubular nanostructures experience an intriguing semiconductor–metal transition at a certain strain, while other α-Te tubular nanostructures are semiconductor with modulable band gap. The electronic properties of α-Te tubular nanostructures under strain modulation can help to understand the properties of new nanomaterials comprehensively, paving the way for future optoelectronic applications. |
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H71.00283: Thermal drift induced artifacts in AFM atomic lattice images DongHyeon Moon, Bo Ram Jeon, Suenne Kim Two-dimensional materials are emerging as next-generation ultra-thin semiconductor device materials. The electronic band structure of these materials is strongly perturbed by mechanical strain. Therefore, many studies on the strain engineering of two-dimensional materials have been conducted recently. The aim of these studies is to control the electronic and optical properties of two-dimensional materials. To determine the effect of strain, it is necessary to investigate the atomic lattice structure accurately. Various scanning force microscopy (SFM) techniques have been used to observe these two-dimensional crystal lattices. In this study, we show that artifacts due to thermal drift in AFM measurements can impede accurate structural interpretation related to strain. In other words, distorted images can lead to incorrect scientific conclusions on the critical strain issues in these atomically thin two-dimensional materials. |
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H71.00284: Phonon dispersion curves for three new MoS2 type monolayers. Fernando Magana, Gerardo-Jorge Vazquez Fonseca, Erick Garces Garcia Using ab initio calculations based on density functional theory, we obtained new structures for MoS2 type monolayers: NbS2, MoP2 and NbP2, not previously reported in the literature. These proposed structures were relaxed to their minimum energy configuration. Then, we calculated the phonon dispersion curves for each one of them. We exhibit the differences with respect of MoS2. The Quantum-Espresso package [1] was used with norm conserving pseudo potentials. |
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H71.00285: Second Harmonic Generation in Nanostructured Metamaterials. Ulises Meza, Bernardo Mendoza Santoyo, W Luis Mochan
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H71.00286: Interplay between structure and physical properties in organic-inorganic 2D perovskites Jean-Christophe Blancon, Hao Zhang, Wenbin Li, Andreas V. Stier, Jacky Even, Aditya Mohite Recent studies have hinted at the importance of dynamic interactions between electronic states and the lattice in organic-inorganic 2D perovskites (2DPs). It is thus critical to understand the interplay between structure and properties during light excitation and in operating devices. Here, we investigate these effects by exploring the 2DPs phase space in terms of both layer thickness and interlayer organic spacer rigidity. We reveal the relation between structural and photophysical properties in 2DPs by correlating structural and optoelectronic spectroscopy at the sub-micron scale and under magnetic field, with support from theory. Our work demonstrates that during photoexcitation strongly bound excitons are generated and their characteristics (mass, size, energy) can be modulated not only by the thickness of the 2D perovskites layers as in classic quantum-wells but also through structural distortions such as perovskite octahedra tilting induced by the organic spacer or crystal edge termination.[1] Similar effects are linked to local compositional changes or artificial interfaces, resulting in giant enhancement of photoemission at the 2DP and WS2 interface.[2] |
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H71.00287: Investigation of Spectral Diffusion due to Static and Dynamic Disorder in Perovskite Thin Films Geoffrey Diederich, Adam Halaoui, Amani H Alfaifi, Sean Shaheen, Mark Siemens Multidimensional coherent spectroscopy (MDCS) is an ultrafast spectroscopy |
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H71.00288: The evolution of ultrafast carrier dynamics in-situ perovskite optoelectronic devices Kanishka Kobbekaduwa, Shreetu Shrestha, Pan P Adhikari, Exian Liu, Wanyi Nie, Jianbo Gao Although significant progresses have been made toward to optoelectronics application including solar cells, large color gamut LEDs, photodetectors, and X-ray detectors, the fundamental understanding of ultrafast carrier dynamics of organic-inorganic perovskite materials remains unclear. The ultrafast dynamics, which reveals some novel physical phenomena such as hot carrier cooling, phonon bottle-neck effect, and many-body problem was widely studied by ultrafast optical spectroscopies, which include pump-probe transient absorption (transmission, reflection, time-resolved THz, optical Kerr effect, and the most popular time-resolved photoluminescence(TRPL). However, it remains a challenge to study the perovskite optoelectronic devices in-situ in an ultrafast fashion. |
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H71.00289: WITHDRAWN ABSTRACT
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H71.00290: WITHDRAWN ABSTRACT
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H71.00291: Pentacene Thin Film Growth Bradley Lockhart, Jessica Bickel Pentacene is a common organic semiconductor with a relatively high conductivity that increases when crystallized. In this experiment pentacene was studied by depositing it on highly ordered pyrolytic graphite (HOPG) using a thermal evaporator and characterizing it with scanning tunneling microscopy (STM). The daily pressure inside the evaporation chamber had small day-to-day variations, between 1 and 7x10-5 torr, which caused significant variations in growth rates. We subsequently developed a method to measure the growth rate immediately before the deposition by opening the shutter of the thermal evaporator to a specific angle so that the growth rate could be measured with a quartz crystal monitor without depositing any material on the HOPG substrate. Examining the resulting depositions with STM, we find several images showing the deposited pentacene either forming into clumps, or into seemingly more ordered track-like patterns. These images were analyzed to find the dimensions of these structures and compared to previously gathered pentacene data from other groups. |
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H71.00292: Characterizing the Crystal Formation and Interdiffusion Mechanisms of PLA/PS/dSMMA Thin Films Suraj Dhulipalla, Mukil Shanmugan, Doris Yang, Xianghao Zuo, Miriam Rafailovich Polylactic Acid (PLA) thin films have emerged as an eco-friendly alternative for nonbiodegradable polymers in industrial coatings. As such, our investigation characterized the interfacial diffusion and crystal formation in thin films (PLA, polystyrene (PS), and deuterated styrene methyl methacrylate (dSMMA) blends) on different substrates. AFM data showed that larger molecular weight PS additives increased crystal size and roughness of PLA-PS annealed samples. In bilayer samples, we found a 32% roughness decrease in PS/dSMMA on PLA compared to PLA on PS/dSMMA samples. SIMS data showed that dSMMA was nearly absent in the PS layer and interfacial thickness increased with dSMMA concentration. Previous studies proved dSMMA’s compatibilizing property in bulk[1]; we prove dSMMA retains this property under confinement without compromising crystallinity. This study shows that substrates influence the roughness and crystallinity of PLA thin films and that dSMMA is an effective compatibilizer of PLA and PS thin films which is a promising sign for future use in bioelectronics. |
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H71.00293: Quasi-static C-V Characterization of Traps in Sputtered Bismuth Selenide FET Protyush Sahu, Junyang Chen, Jianping Wang Bismuth Selenide based devices have gained a lot of attention due to the highly conducting, spin-polarized, topologically protected surface states [1]. They have found a lot of promise in spintronics. Previous works have shown the existence of high charge to spin conversion in sputtered, polycrystalline BixSe1-x [2-4]. This is attributed to the quantum confinement effect in the individual grains of the film. Characterizations have revealed non-idealities from this material due to charge trapping. In this work, we characterize charge traps in FET devices by quasi-static Capacitance-Voltage measurement. The experimental C-V curve shows a hysteretic behavior which is attributed to oxide and interfacial traps. We use the known charge trapping model to calculate the trap densities for different devices. To further understand the physics of random defects, we simulated the electric field in the FET device by 2D finite difference time domain technique (computational electrodynamics) to analyze the E-field uniformity near a defect edge and along the BixSe1-x/SiO2 interface. |
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H71.00294: Investigation of phonon-mediated relaxation within the topological insulator Bismuth Tellurium Chao-Hong Lin, Meng-Ching Lee, Jin-Wei Li, Tsun-I Chen, Chao-Kuei Lee In this work, using double pulses excitation technique, the energy coupling ratio from excitaton laser to coherent phonons of topological insulator bismuth tellurium(Bi2Te3) thin film was characterized. First of all, by analyzing excitation intensity dependent heating temperature of the thin film from the transmission pump probe results, the coherent phonon generation and the energy coupling from laser to phonons were confirmed. The coupling ratio was accordingly estimated and with decreasing nature as increasing temporal spacing between double pulses. Furthermore, the frequency and intensity of the phonon mode were investigated as well. Beside identification of the relaxation characteristic, we also find evidence of phonon-mediated relaxation of the energy density at the Bi2Te3 surface. |
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H71.00295: Weak antilocalization in hexagonal CaTX (T = Cu or Ag, X = Sb or Bi) single crystal SOUVIK SASMAL, Rajib Mondal, Ruta Kulkarni, Bahadur Singh, A. Thamizhavel The hexagonal ABC-type topological semimetals CaTX (T = Cu or Ag, X = Sb or Bi) are currently drawing intense interest due to their intriguing properties. Specifically, the first-principles calculations have revealed that CaAgBi is a topological Dirac semimetal where the Dirac points are located on the rotational axis slightly above the Fermi level and are protected by C6v point-group symmetry [1]. We have grown the single crystals of these topological semimetals. We find that although ABC-type materials crystallize in the hexagonal structure, they adopt different space-groups depending on the T (Cu/Ag) atom. The electrical resistivity shows metallic behaviour following Bloch-Gruneisen relation whereas the Hall resistivity measurements reveal a semimetallic nature with predominantly p type charge carriers. The transverse magnetoresistance measurements reveal the weak antilocalization (WAL) behaviour for fields below 5 T and temperatures less than 100 K. The angular dependence of the magnetoconductance measurements show that CaCuSb and CaAgSb host topologically protected bulk and surface states. We find that WAL is specific to these type of topological semimetals single crystals. |
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H71.00296: Electronic transport properties of doped Bi2X3 (X = Se, Te) single crystals
Shailja Sharma, C.S. Yadav
School of Basic Sciences, Indian Institute of Technology Mandi-175005 (H.P.) India Shailja Sharma, Chadr Yadav The obervation of anomalous Hall effect and the occurrence of superconductivity in doped 3D topological insulators, are some of the very interesting phenomenon in these systems [1-3]. We have investigated the magneto-transport properties of Bi2Se3 and Bi2Te3 single crystals to explore the effect of intercalation and substitution of Fe, Ag, Au, Pt, Pd etc. on the electronic state of the systems. Magnetoresistance of the magnetically doped Bi2Se3 was found to follows Kohler’s rule, suggesting the single scattering rate at all the points on the Fermi surface. Hall effect measurements suggest the consistence doping of charge carriers in the system upon intercalation. Our findings on the weak antilocalization and weak localization cusps in the magnetoresistance and their evolution with dopant concentration bring out the effect of charge transfer or magnetic elements on the topological surface states of these compounds [4]. |
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H71.00297: Tunable anomalous Hall effect in Dirac semimetal Cd3As2 nanowire Shuo Wang, Benchuan Lin, Ying Li, Dapeng Yu, Zhi-Min Liao Recent years, the combination of topology and physics has led to the rapid development of topological physics. Dirac semimetal Cd3As2, with a pair of symmetry-protected three-dimensional Dirac cones, has drawn a lot of attention. Here, we report the experimental observation of tunable anomalous Hall effect in Cd3As2 nanowire. The anomalous Hall signal maximizes near the Dirac point under an applied magnetic field. As the gate voltage is tuned away from the Dirac point, the anomalous Hall signal decreases and eventually disappears. Based on the detailed analysis of the anomalous signal with gate voltage, temperature and magnetic field direction, the observed anomalous Hall effect is attributed to the Berry curvature originated from the Weyl node. |
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H71.00298: Thermodynamic properties of non-trivial topological semimetal CaSn3 K A M Hasan Siddiquee, RIFFAT MUNIR, Charuni Dissanayake, Xinzhe Hu, Swapnil Yadav, Yasumasa Takano, Eun Sang Choi, Talat Rahman, Duy Le, Yasuyuki Nakajima Topological semimetals, a group of gapless electronic phases with topologically stable energy band crossing, give pathways to observe new quantum phenomena. We will report torque magnetometry and heat capacity measurements on CaSn3, which is theoretically proposed to be a non-trivial topological semimetal. We will present a detailed study of band structure for CaSn3 single crystals via torque magnetometry in high magnetic fields up to 35T. We will also present the thermodynamics properties of this material. |
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H71.00299: Growth and transport measurements of nanowires of cubic B20 topological semimetals Nitish Mathur, Andrew Jacob Deruiter, Anastashia George, Mingliang Tian, Song Jin Since the discovery of topological insulators and semimetals, topological materials are key research frontiers in the field of condensed matter physics. One of the examples of the topological material is a Weyl semimetal where two non-degenerate bands cross at a node in a momentum space and acquires a quantized topological charge known as the Chern number. Among them, cubic B20 material systems (such as CoSi, RhSi, AlPt) are found to possess unconventional chiral fermions with higher Chern number and long fermi arcs due to multiple point degeneracies at high symmetry Brillouin points. We have synthesized single-crystal cubic B20 topological semimetal nanowires (NWs) of CoSi and CrGe via chemical vapor deposition (CVD). We conducted magnetotransport measurements with different configuration of applied magnetic field (in-plane/out-of-plane) and current direction to connect quantum topological properties to electronic band structures. We are also performing physical property measurements under high magnetic field. These NW systems can act as the perfect prototypes to understand the impact of surface states and bulk Landau levels on the transport behaviors in finite size topological semimetals. |
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H71.00300: Measurements of cyclotron resonance of the interfacial states in strong-spin orbit coupled 2D electron gases proximitized with aluminum. Prashant Chauhan, Candice Thomas, Tyler Lindeman, Geoff C Gardner, Sergei Gronin, Jan Gukelberger, Roman Lutchyn, Michael Manfra, Peter Armitage The two dimensional electron gas (2DEG) in InAs proximitized by aluminum (Al) is a promising platform for topological qubits based on Majorana zero modes. However, there are still substantial uncertainties associated with the nature of the electronic states at the interfaces of these system. In this work we have investigated a range of In1-xGaxAs heterostructures with Al overlayers using high precision time-domain THz spectroscopy. In magnetic field a prominent cyclotron resonance is observed that can be associated with the response of the interfacial states. Measurements of the THz range complex Faraday rotation allow the extraction of the sign and magnitude of the effective mass, density of charge carriers, and scattering times. We compare the results of measurements with numerical calculations. |
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H71.00301: Pressure-induced superconductivity and topological phase transitions in the topological nodal-line semimetal SrAs3 Erjian Cheng, Shiyan Li Topological nodal-line semimetals (TNLSMs) are materials whose conduction and valence bands cross each other, meeting a topologically-protected closed loop rather than discrete points in the Brillouin zone. TNLSMs have several anticipated properties, such as drumhead-like nearly flat surface states, the possibility of realizing high-temperature superconductivity and so on. Recently, SrAs3 has been theoretically proposed and then experimentally confirmed to be a TNLSM. Here, we report high-pressure experiments on SrAs3, identifying a Lifshitz transition below 1 GPa and a superconducting transition accompanied by a structural phase transition above 20 GPa. A topological crystalline insulator (TCI) state is revealed by means of density functional theory calculations on the emergent high-pressure phase. As the counterpart of topological insulators, TCIs possess metallic boundary states protected by crystal symmetry, rather than time reversal. In consideration of topological surface states and helical spin texture observed in the high-pressure state of SrAs3, the superconducting state may be induced in the surface states, and is most likely topologically nontrivial, making pressurized SrAs3 a strong candidate for topological superconductor. |
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H71.00302: MAGNETISM
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H71.00303: WITHDRAWN ABSTRACT
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H71.00304: Effect of Mn/Fe ratio on the Magnetic and Magnetocaloric Properties of Hexagonal Mn2-xFe1+xGe (0 ≤ x ≤ 1) Heusler Alloys Anil Aryal, Igor Dubenko, Jose Luis Sánchez Llamazares, Jonathan Zamora, Cesar Fidel Sánchez-Valdés, Dipanjan Mazumdar, Saikat Talapatra, Shane Stadler, Naushad Ali In this work, we synthesized bulk Mn2-xFe1+xGe (0 ≤ x ≤ 1) by arc melting and Mn2FeGe melt-spun ribbons by rapid solidification using the melt-spinning technique and investigated their structural, magnetic, and magnetocaloric properties. Room temperature X-ray diffraction analyses show that Mn2FeGe crystallizes into the hexagonal DO19 crystal structure with a small trace of a secondary phase. Mn2FeGe was found to be ferrimagnetic (FIM) with saturation magnetization (MS) values of ~ 1.7 µB/f.u. at ground state which is consistent with the value 2.0 µB/f.u. predicted by the Slater-Pauling rule. Substitution of Fe for Mn in bulk Mn2-xFe1+xGe resulted in a change of the magnetic ground state from FIM to ferromagnetic (FM) with a maximum MS value of 5.1 µB/f.u. for x = 1.0. A tunable Curie temperature (TC) in a wide range of about 200 K, including the near room temperature ones, was found in Mn2-xFe1+xGe which may be important for practical applications. Maximum magnetic entropy changes of - 3.1 Jkg-1K-1 (at µ0ΔH = 5 T) was found at room temperature with a refrigerant capacity of 325 Jkg-1 for x = 0.4. |
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H71.00305: Characterization of ferrimagnetic and spin wave resonance for frequency selective limiting of iron garnet epitaxial films Scooter Johnson, Hans Haucke, Clifford M Krowne, Sanghoon Shin, Syed B Qadri High-frequency devices, such as frequency selective limiters utilize magnetic materials such as yttrium iron garnet (YIG). The requirement of low loss to enable low-power limiting requires the material to be of high-quality single crystal. Unfortunately, the low magneto-crystalline anisotropy in YIG requires a bias magnet to generate the necessary field and frequency conditions for spin wave generation at higher frequency operation. Alternatively, the bismuth-substituted rare earth iron garnet (Bi-RIG) (BiGdLu)3(Fe1-x Gax)5O12 [1] has been found to show low loss (FMR linewidth ~50 Oe) with high anisotropy field (~2300 Oe), thus possibly avoiding the need for external bias [2]. In this study, we characterize and compare the magnetic properties and power dependences of single-crystal YIG and Bi-RIG grown using liquid phase epitaxy using a vibrating sample magnetometer and a coplanar waveguide configuration to assess dc and microwave magnetic properties for potential use in microwave device integration. |
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H71.00306: Antiferromagnetic characteristics in Sr- and Ba-doped phenanthrene superconductors Lei Gao, Guo-Hua Zhong, Hai-Qing Lin It’s very important to clarify the competition between magnetism and superconductivity in alkaline earth metals doped phenanthrene. To achieve this, we have recently studied the crystal structures of Mg-, Ca-, Sr- and Ba- doped phenanthrene and found the most stable ones, which have the lowest energy by first-principles calculations. The result shows that only the most stable Sr1.5phenanthrene and Ba1.5phenanthrene show the weak AFM behavior and the others are non-magnetic. The Sr and Ba atoms intercalate the intralayer region and stay close to benzene-ring. By calculating the different charge density we found that the most stable Sr1.5phenanthrene and Ba1.5phenanthrene structures have charge redistribution and C atoms have gained electrons obviously. From the spin-charge density, we see inequitable phenanthrene molecules have opposite spin polarizations. The density of states (DOS) of the two structures shows that spin-up and spin-down electrons have the unsymmetrical distribution. Combining these results we conclude that the spin polarization of electrons transferring from metal atoms to C-2p orbitals atoms causes the local AFM behavior. This indicates that superconducting Sr1.5phenanthrene and Ba1.5phenanthrene are near the AFM ground state. |
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H71.00307: Magnetism in the honeycomb layers of Na2Ni2TeO6 with chiral layers of Na Nathan Episcopo, Kinley Wangmo, Narayan Poudel, Krzysztof Gofryk, Po-Hao Chang, Rajendra Zope, Ryan Klein, Craig Brown, Thomas Heitmann, Harikrishnan S Nair Low dimensional magnetic lattices offer the possibility of realizing flatbands in the magnon spectrum which can then lead to dissipation-less spin transport and associated magnon Hall effect. One could expect to find a magnon insulator, similar to a topological insulator. In the present work we present a rather less-studied honeycomb material Na2Ni2TeO6 where our preliminary density functional theory calculations of magnetic structure shows departures from reported structures. Our samples of Na2Ni2TeO6 confirmed hexagonal P63/mcm space group with refined lattice parameters, a=5.2023(1)Å and c=11.1552(8)Å. The bulk magnetism for the present sample is characterized using magnetic susceptibility and specific heat, both of which confirm a phase transition at 28 K. Application of 8 T magnetic field only slightly polarizes the transition. We obtain a Curie-Weiss temperature of -9.7(2)K and effective paramagnetic moment of 2.24(4)mB/Ni. This matches well with the spin-only moment of Ni2+. Elastic and inelastic neutron scattering experiments are currently underway and reveal a rather flat spin wave excitation at 5 meV. Combining neutron diffraction with the DFT results, we would arrive at an accurate estimation of the exchange constants for Na2Ni2TeO6. |
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H71.00308: Magnetism of stacked multilayered graphene nanostructures in carbon microspheres Armen Kocharian, Aram Manukyan, Harutyun Gyulasaryan, Eduard Sharoyan, Paul Oyala, Oscar Bernal, Luis Valencia Morphology, structure and magnetic properties of synthesized by pyrolysis (using as precursors metal free phthalocyanine and polyethylene) samples with different concentration of nitrogen in multilayered graphene nanostructures with zigzag edges in carbon microspheres was investigated by XRD, XPS, Raman, HRTEM microscopy, magnetometry, EPR measurements. Studied magnetic characteristics depend on temperature, magnetic field and concentration of nitrogen impurity centers. Prepared sample at Tpyr=700 K demonstrates strong paramagnetism, ferromagnetism and temperature-independent diamagnetism with susceptibility $χ^{Dia}$=-10$^{-6}$ emu/gOe at T=300K. Saturation magnetization vs temperature behavior with maximum magnetization M$_s$ saturation at 20 K closely resembles a spin glass behavior. The itinerant ferromagnetism of π-electrons in narrow impurity bands is interpreted using temperature dependence of spin correlations at zigzag edges in nanographenes. A magnetic hysteresis is also observed under variation of temperature at 100$<$T$<$300 K where magnetization displays diamagnetic character. |
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H71.00309: Screening and Design of Novel 2D Ferromagnetic Materials with High Curie Temperature above Room Temperature zhou jiang, Peng Wang, Xue Jiang, Jijun Zhao Two-dimensional (2D) intrinsic ferromagnets with high Curie temperature (TC) are desirable for spintronic applications. Using systematic first-principles calculations, we investigate the electronic and magnetic properties of 22 monolayer 2D materials with layered bulk phases. From these candidates, we screen out five ferromagnetic monolayer materials belonging to three types of structures: type i (ScCl, YCl, LaCl), type ii (LaBr2), and type iii (CrSBr). Type i is a kind of metallic ferromagnetic material, whereas LaBr2 and CrSBr of type ii and iii are small-bandgap ferromagnetic semiconductors with TC near room temperature. Moreover, the ferromagnetic CrSBr monolayer possesses a large magnetic moment of ∼3 μB per Cr atom, originating from its distorted octahedron coordination. The robust ferromagnetism of the CrSBr monolayer is ascribed to the halogen-mediated (Cr-Br-Cr) and chalcogen-mediated (Cr-S-Cr) superexchange interactions; then, an isoelectronic substitution strategy is proposed to tailor the magnetic coupling strength. Hence, monolayer structures of CrSI, CrSCl, and CrSeBr with notably enhanced Curie temperature up to 500 K as well as favorable formation energy are designed. |
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H71.00310: Griffiths-like phase in a Mn-Intercalated Dichalcogenide Paul Shand, Paul White, Emilia Morosan Static and dynamic magnetic measurements have been performed on polycrystalline Mn0.23TaS2. The measurements indicate the presence of a Griffiths-like phase preceding the paramagnetic to ferromagnetic transition at 57 K. The transition temperature in the clean limit, i.e., for single-crystalline Mn0.25TaS2, is known to be 80 K. dc magnetization measurements on Mn0.23TaS2 indicate a magnetic field-dependent downturn in the inverse susceptibility as a function of temperature below 105 K, a key indicator of the existence of a Griffiths phase. The magnetization also exhibited power law behavior as a function of both temperature and field in this regime. The power-law exponent for M(H) varied with temperature in the Griffiths regime until the critical region was approached. At this point, a modified Arrott plot was necessary to describe the data, giving critical exponents close to the theoretical values for 3D Heisenberg magnets. The second-order ac susceptibility exhibited frequency-dependent peaks in the Griffiths region, which strongly suggests the formation of ordered clusters. The dc magnetization also exhibited logarithmic time decay. The evidence points to a robust Griffiths phase in Mn0.23TaS2. |
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H71.00311: X-ray absorption and magnetic circular dichroism studies of spin-orbital magnetism in the three-dimensional Kitaev honeycomb γ-Li2IrO3 Anna Soper, Kewei Zhou, Nicholas Breznay, Daniel Haskel, Yongseong Choi, Philip Moll, Alejandro Ruiz, James Analytis Transition metal oxides are an exiting platform for exploring novel states of quantum matter. The choice of transition metal and its crystalline structure determine the magnitude of spin orbit coupling and electronic correlations, parameters that can be carefully tuned to create Mott insulators, topological insulators, superconductors and spin liquids. The 5d transition metal oxide lithium iridate γ-Li2IrO3, a Mott insulator and Kitaev spin liquid candidate, displays particularly strong spin orbit coupling, several honeycomb crystal structures, and magnetic ground states that can be tuned with applied pressure and magnetic fields; however, there are still open questions about its electronic structure. X-ray absorption spectroscopy was used to probe the γ-Li2IrO3 valence states and measure spin orbit coupling and crystal field splitting energy scales. In addition, X-ray Magnetic Circular Dichroism measurements were used to extract the spin and orbital content of the iridium magnetic moment. Evidence from these experiments will help to build a more accurate picture of the electronic states driving magnetism in this material. |
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H71.00312: Deviation from nonmagnetic J = 0 state in a pentavalent columnar iridate Sr3NaIrO6 Abhisek Bandyopadhyay, Sugata Ray Strong spin-orbit coupling (SOC) leads to the exotic properties in otherwise banal pool of 'paramagnetic' heavy ion oxides. The 5d4 iridates eventually stirred up a controversy about the origin of magnetism in them. A nonmagnetic J=0 ground state should be realized ideally for a pentavalent d4 iridate in the jj coupling limit, which has never been achieved in any of the reported d4 Ir oxides to date. Briefly introducing the previously handled (by our group) such 5d4 cases with different Ir environments, we here pay serious focus on Sr3NaIrO6, a 5dt2g4 columnar iridate having well separated Ir5+ centers, which is expected to have a singlet J=0 ground state with no net magnetic moment under strong SOC. However, stabilization of such state at moderate SOC is exceptionally fragile to minute external perturbation and enhanced magnetic responses appear. Moreover, the magnetic interaction between these developed magnetic moments becomes another important point. We, in this work, using detailed magnetic and thermodynamic measurements, refute any chance of nonmagnetic ground state in Sr3NaIrO6 compound. Instead, our experimental observations reveal the existence of quantum spin-orbital liquid state down to 40 mK atleast with sufficiently large magnetic moments on individual Ir5+. |
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H71.00313: Quantum spin liquid state in three dimensional metal-organic frameworks Charuni Dissanayake, K A M Hasan Siddiquee, Riffath Munir, Wesley Newsome, Fernando Uribe-Romo, Xinzhe Hu, Swapnil Yadav, Yasumasa Takano, Eun Sang Choi, Yasuyuki Nakajima Quantum spin liquid (QSL) is a massive superposition state of spins, or highly entangled quantum matter in which electrons’ spins fluctuate and remain liquid-like, even at absolute zero temperature. Thus, they preserve spin-rotational symmetry but inhibit long range magnetic-ordering [1]. This novel state of matter attracted much attention in recent years due to the possibility of hosting fractionalized excitations, artificial gauge fields and exotic forms of superconductivity [2]. Here we attempt to uncover the QSL character of the hyperhoneycomb metal-organic framework (MOF) of [(C2H5)3NH]2Cu2(C2O4)3. We reveal the absence of magnetic transition in high magnetic fields up to 35T and magnetic anisotropy via torque magnetometry. Further, we will discuss the exotic nature of the spin liquid ground state and unusual excitations evidenced by the thermodynamic studies performed on candidate QSL [(C2H5)3NH]2Cu2(C2O4)3 down to 1.8K. |
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H71.00314: Structural Determination of Frustrated Double Perovskites Ba2EuMoO6 and Ba2PrMoO6 Jeremy Carlo, Nicholas La Manna Geometric magnetic frustration occurs when magnetic order is inhibited by the arrangement of magnetic ions. In some materials with antiferromagnetic interactions, the moments are arranged in such a way that only certain interactions can be satisfied at once, and are said to be magnetically frustrated. |
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H71.00315: Design and Synthesis of Novel Quantum Magnets Eric Seewald, Lalit Yadav, Sachith Dissanayake, Rabindranath Bag, Sara Haravifard Due to recent advances in the field of topological quantum spin liquids, there is an increasing demand for high quality single crystals of frustrated magnets that host such exotic behavior. Here we present our recent results of such efforts. Solid-state reactions are used to synthesize polycrystalline samples of quasi-2D and 3D frustrated quantum magnets, whose purity is confirmed by powder x-ray diffraction analysis. With a pure polycrystalline sample, the optical floating zone and chemical vapor transport techniques are used to produce high quality large single crystal samples. We use an array of thermal and magnetic measurements as well as single crystal x-ray diffraction to characterize the samples, before performing advanced neutron and synchrotron x-ray scattering experiments at national user facilities. |
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H71.00316: Longitudinal spin fluctuations in complex ordered states with a Landau-Ising model Harry Keen, Andreas Hermann Classical local-moment models, like the Heisenberg and Ising models, are often used in combination with ab initio calculations to predict the magnetic properties of real materials. These can often perform poorly for metals, where fluctuations in the magnitude of the moment are important. Modelling longitudinal spin fluctuations phenomenologically: by allowing spin magnitudes to vary constrained by a Landau-like on-site potential, has been applied frequently by other authors and tends to improve agreement with experiment. |
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H71.00317: Sign reversal of anomalous Hall effect in polycrystalline ultrathin Mn3Pt films JOYNARAYAN MUKHERJEE, Satyaki Sasmal, Karthik Raman The kagome structure of noncolinear antiferromagnet (NC-AFM) gives rise to finite Berry curvature which consequences many novel phenomena such as anomalous Hall effect (AHE), magneto optical Kerr effect and topological Hall effect1. Although AHE has been reported in epitaxial thin films of NC-AFM, Mn3Pt2, here we present the sign reversal of AHE in polycrystalline Mn3Pt films varying the thickness of the film and measurement temperature. |
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H71.00318: Magnetic anisotropy in the rare-earth honeycomb lattice YbCl3 Huibo Cao, Erxi Feng, jie xing, Yan Wu, Yaohua Liu, Eve Emmanouilidou, Chaowei Hu, Tianci Song, Ni Ni The Kitaev quantum spin liquid (KQSL) is an exact solvable exotic state with bond-directional interactions in a honeycomb lattice [1]. Its potential applications in quantum information field attract a lot of attention. So far only a few KQSL candidates are available, such as honeycomb lattices α-RuCl3 and Na2IrO3 with strong spin-orbital coupling 4d (Ru) and 5d (Ir) elements [2-4]. All these lattices show the long-range zig-zag magnetic order at low temperature instead of KQSL states. Recently we found a new Kitaev candidate, the rare-earth honeycomb lattice YbCl3 with an effective spin-1/2, which presents a short-range magnetic order around 1.2 K and another kink at 0.6 K [7]. We investigated the magnetic ground state and magnetic anisotropy of YbCl3 using unpolarized/polarized neutron diffraction techniques, which will be the focus of the presentation. |
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H71.00319: Phase transitions in novel Li-containing honeycombs, Li8Cr2(Te/Sb)2O12 Hector Mandujano, Sandra Gonzalez, Narayan Poudel, Krzysztof Gofryk, Stuart Calder, Harikrishnan S Nair Honeycomb frameworks of Li8M2(Te/Sb)2O12 (M = transition metal), present interesting magnetic phenomena related to frustrated two-dimensional lattices of spins. In the present work, polycrystalline Li8Cr2(Te/Sb)2O12 were synthesized by standard solid-state route. Powder X ray diffraction patterns were recorded to check the phase formation and purity. C2/m space group was confirmed using Rietveld analysis and lattice parameters are determined to be a=5.141Å, b=8.884Å, c=5.143Å, β=109.5Å for Li8Cr2Sb2O12, and a=5.128Å, b=8.850 Å, c=5.151Å, β=109.8Å for Li8Cr2Te2O12, presenting diminished unit cell sizes compared to that of Li8Co2Te2O12 are a=5.226Å, b=8.892Å, c=5.160Å, β=110.9Å. In the case of Li8Cr2Sb2O12 a magnetic phase transition is present at 7.4 K as determined from the derivative, dCp/dT. A similar transition is found in Li8Co2Te2O12 at 9.5 K. Neutron diffraction is underway for comprehending cationic ordering, crystal, and magnetic structure of Li8Cr2(Te/Sb)2O12 as well as its mixed occupancy of the 4g Wyckoff position in the C2/m space grpup. Our experimental results will highlight the magnetism of the honeycomb layers of Cr and the ionic diffusion of inter-layer Lithium and will be of interest to magnetism as well as battery research. |
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H71.00320: Antiferroelectric antiferromagnetic type-I multiferroic Cu9O2(SeO3)4Cl6 Ting-Wei Kuo, Hung-Cheng Wu, Zong-Heng Yang, D. Chandrasekhar Kakarla, Kseniia Denisova, O.V. Maximova, Chi-Hung Lee, Wen-Hsien Li, helmuth berger, Chin-Wei Wang, Chung-Kai Chang, Yu-Chun Chuang, Jiunn-Yuan Lin, Melissa Gooch, Ching (Paul) W Chu, Hung-Duen Yang, A. N. Vasiliev We report that Cu9O2(SeO3)4Cl6 is a new multiferroic compound. Comprehensive studies of this compound have been carried out on single crystals as well as polycrystalline samples. Magnetic susceptibility c and specific heat C with H || c–axis both reveal an anomaly at TN = 37 K associated with the long-range antiferromagnetic order. However, no signature of this phase transition is seen with the H || b-axis, providing evidence of the anisotropic nature of its magnetic properties. The results of c measurements are consistent with the temperature evolution of the intensity of magnetic reflections from the neutron diffraction experiments. The magnetic structure derived from neutron scattering measurements shows that half of the Cu(5) ions carrying no moments. Furthermore, an anomaly in the dielectric constant near TN and observable magnetoelectric coupling below TN are found. At high temperatures, a dielectric peak at TE = 267 K is identified with no measurable spontaneous polarization below TE, thereby suggesting an antiferroelectric order. A step-like anomaly seen in c(T) at TE hints at weak spin-lattice coupling. Concomitantly, high-resolution temperature-dependent synchrotron x-ray diffraction experiments elucidate a local structural distortion at TE. |
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H71.00321: Characterization of GaTa4Se8 single crystal with Jeff=3/2 ground state magnetic molecular Choongjae Won, Seunghwan Do, Jae-you Kim, Jae-Hoon Park, Sang-Wook Cheong The geometrical spin frustration in the tetramer of lacunar spinel is a good subject for exploring the quantum spin liquid. In tantalum lacunar spinel, GaTa4Se8, there are molecular Jeff = 3/2 ground state and curious non-magnetic state with Jahn-Teller distortion [1]. Recently, we successfully grown the high quality of GaTa4Se8 single crystal, and studied by characterization of physical properties and inelastic neutron scattering. Temperature dependence of those characterization shows the difference between structure transition with orbital ordering, and indicates that gapped excitation already exists at higher temperature than orbital ordering temperature TS ~53 K. |
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H71.00322: First-principles study of the Ir-Ir dimerization effect on the magnetic phase diagram of honeycomb iridates Kevin Lucht Honeycomb lattice iridates have been a promising candidate for the realization of the Kitaev spin model. However, the addition of off-diagonal and Heisenberg interactions result in magnetic ordering at low temperatures, causing the quantum spin liquid (QSL) phase to remain elusive. The application of hydrostatic pressure to the system has shown the loss of magnetic ordering, and although indicative of a spin liquid phase, has been shown to be caused by dimerization between iridium ions. Using ab initio calculations, we intend to identify the pressure region in beta-Li2IrO3 and alpha-Na2IrO3 where the symmetry lowers in the systems, marking the onset of dimerization. Subsequently, using exact diagonalization (ED) and cluster mean field theory (CMFT) on a periodic cluster, we will identify the ground state of the dimerized system and explore its phase diagram and spin correlations. |
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H71.00323: Crystal structure and magnetic behavior of NdAlGe. Chetan Dhital, Ramakanta Chapai, Sunil Karna, Qiang Zhang, Yan Wu, Rongying Jin, Huibo Cao, David P Young, John Ditusa Rare earth compounds are known to exhibit varieties of exciting electronic and magnetic properties arising from complex interplay of conducting charges, usually derived from s- or p-like bands and more localized f-electrons. Added variety of interesting states comes from differences in lattice symmetry, spin-orbit interactions, crystalline electric fields, and the related magneto-crystalline anisotropy. A recent addition to such exciting properties is the theoretical prediction and experimental verification magnetic Weyl fermion state in RAlGe (R=Rare earth) family of compounds. Previous investigations of this class of compounds were limited to R=La, Ce and Pr. In this work, we extend this line of inquiry to isostructural NdAlGe to explore how these electronic and magnetic properties vary as the size of the rare earth element and consequently the position of the f-electron states with respect to the Fermi level is varied. I will present the crystal structure and magnetic behavior of NdAlGe. |
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H71.00324: Raman Spectroscopy of layered magnetic systems Mainak Palit, Anudeepa Ghosh, Subhadeep Datta Metal phosphorus trichalcogenides (MPX3) have emerged as an exciting class of layered magnetic 2D materials for future spintronics. Retaining long range magnetic ordering even in the exfoliated few layers is the hallmark of 2D magnetism. Raman spectroscopy can be an effective probe to identify low-energy phonon modes and possible spin-phonon coupling in reduced dimension from bulk crystal. In this study, temperature dependent Raman Spectra of exfoliated iron phosporous trichalcogenides (FePS3) flakes reveal a distinct shift of the large wave number phonon peaks towards higher wavenumber as temperarure decreases. A clear deviation from standard anharmonic behavior below characteristic Néel temperature (TN) is also observed. Other low wave number symmetry modes exhibit temperature dependent non-anharmonic self-energy as a function of layer thickness below TN, related to the strong spin-lattice interaction due to short-range magnetic order. Energies and symmetries of the observed Raman-active modes are in agreement with DFT calculations. Below TN low wave number broad mode in the paramagnetic state(T>TN) splits into multiple distinct modes and evolve further into a possible magnon mode. We believe these results will pave way for possible spintronic applications exploiting magnons. |
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H71.00325: Quantum magnetization reversal studied in S/F/S Josephson φ0 junction Gwang-Hee Kim We study quantum tunneling of magnetization in the presence of the bias current and the magnetic field along the general direction in the Josephson φ0 junction. With account taken of the influence of the superconductivity on the ferromagnet in the kelvin or subkelvin range, we present the analytic formulas of the tunneling rate in the uniaxial and nonuniaxial symmetries, and find that the tunneling exponents depend on three parameters related to the current and the magnetic field. We demonstrate that the current is equivalent to the effect of the magnetic field along the easy axis and the tunneling rate can be shifted by the bias current in the presence of such an external magnetic field. These features are expected to be observable with existing experimental techniques. |
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H71.00326: Slowed relaxation of the magnetism through dilution into paramagnetic mediums Ian Moseley, Joseph Zadrozny Single molecule magnets (SMMs) represent the smallest magnetic domains (a single molecule) and as such have potential applications in information storage, quantum computing, and spintronics. Extending the lifetime of the magnetic relaxation is critical to applications of these molecules. Dilution of SMMs is a common strategy employed to extend magnetic relaxation and is typically carried out by dilution into a solvent or cocrystallization with an isostructural diamagnetic species. Herein, we report the first known example of extended magnetic relaxation through dilution into a paramagnetic medium. Using the canonical SMM [PPh4]2(Co(SPh)4), dilutions into the isostructural paramagnets [PPh4]2(M(SPh)4) (where M = Ni, Fe, and Mn) were made by cocrystallization. We show that across a range of concentrations, both Fe and Ni perform like the diamagnetic Zn congener, whereas the Mn dilution results in an accelerated relaxation. Dipolar interactions beetween spin centers are considered and we hypothesize that the observed relaxation enhancement can be attributed to low temperature magnetism of the paramagnetic diluents. |
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H71.00327: Charge Transfer in Single-Molecule Magnetic Complexes [Mn12O12(O2CR)16(H2O)4] Dmitry Skachkov, Jia Chen, George Christou, Xiaoguang Zhang, Samuel Trickey, Hai-ping Cheng Single-molecule magnetic (SMM) complexes [Mn12O12(O2CR)16(H2O)4], with R=-H, -CH3, -CHCl2, -C6H5, have twelve Mn atoms in the core, eight of them are in 3+ charge state and located at peripheral ring of the molecule, while the four remaining Mn atoms in the center of the molecule are in 4+ charge state. When the SMM molecule is receiving the additional electron by excitation, this electron is localizing on one of the peripheral Mn atom, and the charge state of this atom is changing from Mn3+ to Mn2+, what is confirmed by experiment measuring the Mn-O bond lengths [Inorg. Chem. 2017, 56, 10706]. In order to develop the SMM with high catalytic activity, it is very important to know the energy barrier for electron transfer from Mn2+ atom to another Mn3+ atom located on diametral site of the molecule, in order to stimulate oxidation reaction. We are calculated the minimum energy pathway for electron transfer in tunneling regime calculating the energy barrier for electron motion by plotting the profile of electrostatic potential along possible pathways. In the talk we will discuss the pathways for electron transfer in SMM for different ligands. |
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H71.00328: WITHDRAWN ABSTRACT
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H71.00329: Electron Spin Resonance of Heisenberg Spin Chains of Four Ti Atoms Soo-hyon Phark, Kai Yang, Taner Esat, Andreas Heinrich, Christopher Lutz Heisenberg spin chain (HSC) is a one-dimensional circular array of spins, where the nearest neighbors are exchange-coupled. Quantum transitions between the energy eigenstates of such spin chains are well understood by the creation and annihilation of spin wave quanta. Using a low temperature (1.1K) scanning tunneling microscope (STM), we composed two circular spin chains of four hydrogenated Ti atoms, spin-1/2 atomic species, on MgO surface by atom manipulation techniques. The nearest neighbor couplings are antiferromagnetic and tuned to be 6 and 25 GHz by interatomic distance control. We performed electron spin resonance (ESR) combined with the STM on the spin chains. The measured ESR spectra show a remarkable consistency with the quantum transition probabilities calculated from the Heisenberg spin Hamiltonian, which identifies the energy eigenstates of the spin chains. We discuss the experimental data by employing the spin wave theories. This work suggests that our Ti spin chains deserve an ideal exchange-coupled quantum spin system. In addition, this work demonstrates an experimental approach plausible to creation and control of quantum phenomena in artificial spin structures. |
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H71.00330: Thermal spin-transfer torque driven by Chirality Induced Spin Selectivity effect in layered chiral hybrid perovskite Kyunghoon Kim, Eric Vetter, Liang Yan, Wei You, Dali Sun, Jun Liu Thermal spin-transfer torque (STT), the transfer of the spin current mediated by heat current, provides a new way to control the orientation of nanomagnets. The recent discovery of the Chiral-Induced Spin Selectivity (CISS) effect offers an opportunity to create spin current in chiral materials without the need of ferromagnet elements, e.g., chiral (left- or right-handed) molecules. In the presence of electron transport mediated by heat current, the chiral materials would produce a spin current via CISS effect, of which the spin polarization determined by handedness of the material. Here we study the CISS effect in solution-processed, 2D-layered, hybrid perovskite materials incorporating chiral molecule ligands, sensed by the thermal STT signal using ultrafast Time-Resolved Magneto-Optical Kerr Effect (TR-MOKE) technique. The chirality-dependent precession of the magnetization in the ferromagnet layer on top of layered chiral hybrid perovskites were observed which is attributed to the CISS effect. Our work opens a new route for the use of layered chiral hybrid perovskite materials for novel STT devices. K.K., E.V., and L.Y. contributed to this work equally. |
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H71.00331: Electronic structure and magnetism of monolayer Janus transition metal dihalides Chase Hanson, Antia S. Botana Based on first-principles calculations, the evolution of the electronic and magnetic properties of transition metal Janus dihalides MXY (M= V, Mn, Fe, Co, Ni; X, Y = Cl, Br, I) is analyzed at the monolayer limit. A variety of magnetic ground states is obtained as a result of the competition between direct exchange and superexchange. We show how structural symmetry-breaking plays a crucial role in the magnetic and electronic properties of 2D magnetic materials. |
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H71.00332: Spinon-magnon interaction in an antiferromagnet with alternating antiferromagnetic and ferromagnetic quantum spin chains Heda Zhang, Zhiying Zhao, Vasile O Garlea, Tao Hong, Dominique M Gautreau, Amartyajyoti Saha, S D Mahanti, Turan Birol, Xianglin Ke The concepts of quasiparticles and collective modes have been successfully applied to describe low-energy excitations in physics. In conventional magnets low-energy excitations are carried by spin waves, represented by massless bosons called magnons with S = 1. However, in one-dimensional antiferromagnetic quantum spin (S = 1/2) systems, quantum fluctuations destroy LRO in the ground state and magnons do not exist. Instead, the low-energy excitations are known as spinons, with S = 1/2 . Although both magnons and two-spinon continuum have been observed in several quasi-one-dimensional antiferromagnets, magnons and spinons do not coexist in the same energy range. Here, we report the observation of coexistence of magnon and spinon excitations in Cu2(OH)3Br, a quantum antiferromagnet consisting of nearly decoupled, alternating ferromagnetic and antiferromagnetic S=1/2 chains. Importantly, the excitation spectra of both the magnetic chains emerge in close energy range and cross over each other, enabling strong spinon-magnon interaction. |
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H71.00333: Synthesis of Amorphous Soft Magnet using the IR image furnace Deok Young Lee, Daehwan Park, Jun Han Lee, Yoon Seok Oh Study of soft magnets has been an important research topic because of their various applications such as transformers, magnetic shielding, transducers, and large variety of apparatus. Amorphous soft magnets are conventionally synthesized by using melt-spinning method, in which molten metal is cast onto a fast-rotating copper wheel and could be cooled down with 105-106 K/sec to form highly amorphous state. However, constitutionally, the melt-spinning method yields potential contamination from the copper wheel. An improved synthesis method is required to get highly pure and ultimate soft magnet. In order to avoid the potential copper contamination, we have synthesized soft magnet using the IR image furnace. The IR image furnace focuses high-power infrared light from two or four lamps in the middle of two ceramic rods with two or four mirrors and develops floating molten zone, where provides a crucible free environment. By control of lamp power, travelling speed, rotation speed of rods, and gas conditions, the amorphous alloy could be synthesized without copper contamination. Here we present morphology, chemical, and magnetic properties of amorphous soft magnet synthesized by the IR image furnace. |
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H71.00334: Synthesis and structural and magnetic properties of Sr1-yPryFe12-xCoxO19 nanocomposites prepared via auto combustion technique Mridul Bhattarai, Jiba Nath Dahal Sr1-yPryFe12-xCoxO19 (x= 0.0- 1.5 and y= 0.1- 0.3) polycrystalline samples were prepared via auto combustion method and analyzed with respect to their structural and magnetic characteristics. The possibility of simultaneous substitution of Fe3+ by Co2+ was verified for low substitution degrees. At higher substitution of Co2+, a secondary soft magnetic phase CoFe2O4 is observed. The room temperature magnetic parameters derived from hysteresis loops showed that the saturation magnetization of Sr1-yPryFe12-xCoxO19 increased with the increase in cobalt content, and a concomitant reduction in coercivity values is controlled by substituting Pr3+ for Sr2+. Mr value increases with increasing Co2+ content indicating the presence of an exchange coupling between magnetic hard and soft phases of the composite. The highest magnetization 61.17emu/g and coercivity Hc 3.98 kOe is observed in y= 0.1, x= 1 content. The coercivity observed is about |
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H71.00335: permanent magnet properties of Fe5C2 from first principles LI YIN, David Parker Iron carbides, such as Fe3C, Fe2C and the Hagg carbide Fe5C2 are commonly produced in steel-making and in fact often play an important role in strengthening such steel. Here we study the permanent magnet properties of Fe5C2 from first principles, focusing on the magnetization and magnetic anisotropy – two indispensable components of a permanent magnet material. We find a substantial magnetization exceeding 1.5 T, along with a significant magnetic anisotropy exceeding 1 MJ/m3 (here defined as the energetic difference between the magnetically easiest and hardest directions). While the anisotropy for an intermediate direction is much smaller, likely precluding the use of Fe5C2 for permanent magnet applications, the 1 MJ/m3 anisotropy value is rather significant for a material containing only relatively light elements such as Fe and C. It is in fact more than half again as large as the value for hcp Co. We discuss the implications of these results for permanent magnet applications. |
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H71.00336: Detection of magnetic domain wall of YIG with scanning diamond NV center probe Yuta Kainuma, Rui Wang, Kunitaka Hayashi, Kenichi Nakashita, Toshu An Probing and imaging of the magnetic domain structure at the nanoscale are important to understand the basic physics of the magnetic interaction, and for the application in the spintronics field. The nitrogen-vacancy (NV) center; spin state of a defect structure in diamond, is attracting much attention for its novel spin sensing ability at nanoscale and room temperature conditions. We developed a scanning NV center spin sensing probe combined with atomic force microscopy (AFM) based on quartz tuning-fork resonator. Electron spin resonance (ESR) signal from the apex of the NV center probe can be detected optically (optically detected magnetic resonance, ODMR) via confocal microscope setup. A diamond probe (φ 4 µm, length 10 µm) hosting an ensemble of NV centers is glued at the end of the AFM probe enabling simultaneous measurements of the ESR and topographic images of the sample. Magnetic insulator of yttrium iron garnet (YIG) was used for the magnetic film sample that shows magnetic domain wall structures with a micrometer scale under zero external magnetic field. The stray magnetic field from magnetic domain walls was measured with the scanning NV center probe. |
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H71.00337: A Low-Cost Vibrating Sample Magnetometry Based on Audio Components Babu Sankhi, Emrah Turgut Measurement of magnetization is an important characterization step for magnetic materials to understand their fundamental properties and to utilize in industrial applications[1]. In this project, we construct a cheap and versatile vibration sample magnetometer (VSM) using the sound card. We tested our VSM for the hysteresis loops of three distinct magnetic samples: bulk Nickel piece, perm-alloy thin film with an easy- plane anisotropy, and Co/Pt multilayer with perpendicular magnetic anisotropy. The magnetizations of corresponding loops are analyzed at different frequencies and, the noises are also measured and compared for two methods. Although sound card performance is not very good for the frequencies below 20 Hz due to the cut-off frequency, its sensitivity is approximately 7 times better than that of lock-in amplifier at higher frequencies up to 60 Hz. The measured sensitivity of our sound card based VSM is of the order of emu, which is better than the sensitivities obtained in the previous similar experiments [2] at room temperature. |
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H71.00338: Resolution Increase and Faster Phase Identification for Electron Magnetic Imaging Md Mazharul Islam, Emrah Turgut, Nathaniel Berry A detailed imaging of magnetic skyrmion arrangement allows us to understand the interactions in them and their dynamics, which can pave the way to the low power spintronics device [1]. Lorentz Transmission Electron Microscopy is an effective way for imaging the internal magnetic properties of a material [2]. The phase shift of the electron beam has a relationship with the magnetization distribution of the nanostructure that is based on Aharonov-Bohm Effect. Here, we are using several methods to get the electron phase shift caused by the complex magnetization distribution. We then reconstructed the magnetization using a model based iterative algorithm [3]. For getting an accurate magnetization distribution, cost function minimization analysis was done. We then compared the accuracy of the reconstructed magnetization from the electron phase shift from different forward process. Here, our methods reduce the artifacts that are usually seen in magnetization reconstruction process. |
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H71.00339: Emerging Widefield Magnetic Microscopy Applications with Nitrogen-Vacancy centers in Diamond Pauli Kehayias, Tzu-Ming Lu, Andrew M Mounce We will discuss using magnetically-sensitive nitrogen-vacancy (NV) color centers in diamond for widefield magnetic microscopy, a technique which offers sub-micron spatial resolution, high magnetic moment sensitivity, and parallel magnetic readout in ambient conditions. NV magnetic imaging is being used to study superconductivity, current flow in 2D materials, magnetic domain structures, and other condensed-matter physics applications. With the objective of exploiting the NV magnetic imaging advantages in a wider array of scientific problems, we will report on our recent progress using NV imaging for applications relating to synthetic micromagnets, magnetic materials, hardware security, and electronics fabrication. |
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H71.00340: Tabletop EUV magnetic linear dichroism spectroscopy on thin-film antiferromagnetic chromium across the 3p absorption edge Peter Johnsen, Christian Gentry, Sinead Ryan, Margaret Murnane, Henry Kapteyn We present the magnetic linear dichroism (MLD) reflection spectra measured on antiferromagnetic Chromium by use of a tabletop high harmonic generation (HHG) source across the 3p absorption edge. The spectra were obtained by rotating the field-cooled direction of the magnetization 90 degrees relative to the incident polarization angle. Furthermore, we investigate the effect as a function of both film thickness and angle of incidence. |
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H71.00341: Tunneling Magneto Resistor Nano-columns Dereje Seifu Nanowires inside carbon nanotubes (CNTs), nano-columns, and thin films of ferromagnet /insulator/ ferromagnet (FM/I/FM) tunneling magnetoresistance (TMR) were synthesized using magnetron DC/RF sputtering [1]. Nanowires were synthesized inside CNTs using glancing angle deposition. The magnetic properties of nanowires, nano-columns and planar nano-metric thin films of FM/I/FM showed similarities including two-fold magnetic symmetry. Nanowires of Fe/MgO/Fe showed enhanced magnetic properties in particular a high increase in coercive field, 754% higher compared to planar thin films of Fe/MgO/Fe [1]. This could be due to shape anisotropy in nanowires, which play an important role in coherence. TMR of nano-columns and nano-metric thin films of FM/topological/FM are other examples studied. TMR is a macroscopic phenomenon that can only be explained by quantum mechanics, where electrical resistance varies when an external magnetic field is applied parallel to the tri-layer system. |
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H71.00342: Magneto Restrictive Sensor Dereje Seifu, Asha J Hall Magneto restrictive based sensors can be used for diagnosis and prognosis of cracks and creep in vital parts of several mechanical systems. One material studied extensively for this application is Tb0.3Dy0.7Fe2 (TFD). We studied the structural and magnetic properties of micro-particles of TFD embedded inside reinforced carbon fiber polymer (RCFP) using VSM, TMM and MFM. Results show enhanced magnetic properties for TFM when embedded inside RCFP and a two-fold magnetic symmetry. To get a deeper understanding of the structural and magnetic properties of TFD, thin films were synthesized using magnetron DC/RF sputtering. Study of surface magnetism of films processed at a substrate temperature of 250 oC using MOKE revealed a four-fold magnetism. Results from magnetic and structural measurements will be presented. |
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H71.00343: Structural, interface, and device properties of some Bi2Se3-based spintronic heterostructures. Yub Raj Sapkota, Duston Wetzel, Dipanjan Mazumdar Incorporating Topological Insulators in spintronic heterostructures and devices have gained interest due to several recent observations of greater spin-orbit torque compared to heavy metals. However, strong tunnel magnetoresistance (TMR) behavior has not been established with TIs compared to standard spintronics interfaces such as CoFeB-MgO. In this work, we have systematically investigated the structural, interface properties of prototypical a TI material (Bi2Se3) with normal Ferromagnets such as Co. Bilayer (Bi2Se3/Co) and TMR heterostructures (Co/Bi2Se3/Co) was fabricated using magnetron sputtering and their structure and interface investigated using X-ray diffraction and X-ray reflectivity method. Systematic thickness and substrate dependence studies with different growth and post-deposition annealing conditions have been carried out. We show that a sharp Bi2Se3/Co interface is possible, but annealing may lead to significant interdiffusion. Shadow mask techniques were incorporated to define micron-sized TMR devices. Detailed transport and magnetotransport and current-voltage characteristics will be discussed. |
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H71.00344: Magnetic and Electronic Materials towards Realization of a FET based on Spin-Orbit Torques Phillip Dang, Zexuan Zhang, Joseph Casamento, Xiang Li, Jashan Singhal, Darrell Schlom, Daniel Ralph, Huili Xing, Debdeep Jena The spin-orbit torque field effect transistor (SOTFET) is a recently proposed device that combines the spin-orbit-torque mechanism for writing magnetic memories with semiconductor transistors that are ubiquitous in logic. The SOTFET utilizes a magnetoelectric multiferroic to couple a SOT-controlled ferromagnet to the semiconducting channel. Therefore, this magnetic device may access the orders-of-magnitude on/off ratio of transistors, giving it the potential to combine memory and logic. It’s realization, however, relies on the delicate interplay between topological insulating, ferro/ferrimagnetic, multiferroic, and semiconducting materials. In this talk, we discuss the material parameters and candidates that show promise for integration into a SOTFET and give an overview of the material advances towards realizing the device. |
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H71.00345: Large Unidirectional Magnetoresistance in Topological Insulator/Ferromagnet Bilayers Duston Wetzel, Yub Raj Sapkota, Dipanjan Mazumdar
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H71.00346: Fabrication and characterization of CuO-doped Ni-Co-Zn ferrite composites for RF applications. Poonam Lathiya, Jing Wang With the recent advancements related to imminent rollout of 5G and IoT technologies, there is a growing demand for soft magnetic materials for different applications such as antennas, circulators, inductors, interference suppressors and wireless power transfer etc. Ni-Co-Zn ferrites exhibit excellent soft magnetic properties such as high resistivity, high permeability and low magnetic loss for RF applications. To meet the performance specifications for aforementioned applications, Ni-Co-Zn sheets with a high permeability and low magnetic loss is desired. In this work, we present a novel method to prepare thin Ni-Co-Zn ferrite sheets with high permeability and low magnetic loss for RF antenna applications. Ni-Co-Zn ferrite powders were prepared by solid state synthesis. Different CuO wt% were doped in Ni-Co-Zn samples. Toroidal samples made from powders under different level of hydraulic force were sintered in air. Enhancement in the resonance frequency was achieved by doping of copper oxide (0 to 10 wt%) in Ni-Co-Zn ferrite. The permeability decreases from 7 (0 wt%) to 5.3 (10 wt%) along with increase in resonance frequency from 300 to 530 MHz. Magnetic loss of 0.04 achieved at 530 MHz frequency. Ni-Co-Zn sheets were prepared with same optimized conditions for RF antennas. |
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H71.00347: Effect of Demagnetization Method on Remnance Magnetization States in Metallic Ferromagnets Jennifer Freedberg, E. Dan Dahlberg Parametric plots of the remagnetization versus demagnetization remnances, commonly called Henkel plots, were constructed for four metallic ferromagnets. These were compared to Wohlfarth’s simple model for noninteracting particles [1]. Three different paths to a net zero magnetization state (AC and two types of DC demagnetization) were explored for all the samples and in addition two of the samples were thermally demagnetized. These results present a useful comparison between metallic and particulate ferromagnetic systems, and how fundamental differences in their magnetization processes affect subsequent measurements. While adherence of our data to Wohlfarth’s model was poor for several paths to zero magnetization, many similarities between our data and models including magnetic interactions were found [2, 3]. |
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H71.00348: Classical mechanism for the anomalous enhancement of Hall resistivity during magnetization reversal Christopher Ard, Hua Chen, Olivier Pinaud Certain bulk or synthetic ferromagnetic conductors with broken inversion symmetry show a characteristic hump in the hysteresis curve of the Hall resistivity, which is commonly ascribed to the topological Hall effect due to the formation of skyrmion lattice in finite fields. Here we argue that the hump could also be due to classical mechanisms associated with transport in random media. By modeling a 2D inhomogeneous ferromagnetic conductor using a random resistor network model, we are able to show that an anomalous enhancement of the Hall resistivity can arise before the ferromagnet is fully switched by a perpendicular magnetic field. The qualitative behavior is further analyzed by solving the diffusion equation with correlated disorder perturbatively. |
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H71.00349: Ferromagnetic Resonance Studies of MnZn Ferrites/Polymer Composite Materials. Paul Couture, Robert Camley, Karen Livesey, Zbigniew J Celinski We characterize MnZn ferrite particles embedded in a polymer for use in low frequency EMF emissions shielding. The ferrites particles are approximately 1.2 µm in diameter and embedded in PVC resin in various concentrations: 10% - 70% by weight. The composite undergoes an extrusion process which creates a 0.6 mm thick slab and orders some of the particles along the extrusion direction. This creates an easy axis along the extrusion direction with an associated anisotropy. We characterized the ferromagnetic resonance absorption peaks with broad-band FMR, 1-30 GHz, and cavity based FMR systems. Comparing the results to the expected FMR peaks for measurements along the easy and hard axes, and normal to the slab, using the Landau-Lifshitz-Gilbert equation provides some interesting irregularities. Samples with high ferrite concentrations, Kittel's equation for thin film resonance can be used to describe the FMR frequency vs. field dependence. For low ferrite concentrations the resonance conditions have to be modified to account for an effective thickness beyond the normal filling factor correction associated with presence of a matrix. These results indicate the effective demagnetizing factors, determined by the spatial extend of the RF fields, can describe the observed FMR absorption. |
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H71.00350: Modulation of heavy metal/ferromagnetic metal interface for high-performance spintronic devices Shouzhong Peng, Daoqian Zhu, Jiaqi Zhou, Boyu Zhang, Anni Cao, Mengxing Wang, Wenlong Cai, Kaihua Cao, Weisheng ZHAO Spintronic devices such as magnetic tunnel junction and skyrmions have attracted considerable attention due to features such as nonvolatility, high scalability, low power, and high speed. Here we demonstrate that the heavy metal (HM)/ferromagnetic metal (FM) interface is playing an essential role in spintronic devices and the properties can be significantly improved by proper modulation of this interface.[1-5] Firstly, we investigated the effect of HM/FM interface on the perpendicular magnetic anisotropy (PMA) of several structures.[4-5] Then experimental and theoretical investigations of the HM/FM interface for high tunnel magnetoresistance (TMR) ratio were presented.[2] Next, spin-orbit torque (SOT) switching were discussed with emphasis on low-power and field-free SOT switching.[3] Subsequently, the investigations of Dzyaloshinskii-Moriya interaction (DMI) in different HM/FM systems were presented. This work provides guidelines for high-performance spintronic devices and an outlook for potential applications. |
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H71.00351: Evolution of Skyrmion state from Helical state in MnxTaS2 Rabiul Islam, Peng Li, Marijan Beg, Hans Fangohr, Guoxing Miao Skyrmion-based memory and logic devices are promising to overcome the limitations of the conventional data storage and information processing devices. However, the number of materials hosting magnetic skyrmions is very limited. Therefore, the discovery of new materials is an important avenue of research. In this work, we explore whether the skyrmion state can be an equilibrium state in MnxTaS2 (MTD) as well as how does the skyrmion state emerges from the helical order with its helical length of 95 nm. By applying an external magnetic field, we were able to modulate the helical period and eventually obtain the skyrmion state. Our findings demonstrate the existence of the skyrmion state in MTD magnetic materials as well as the evolution path. 3D view of magnetic moments gives a picture of the Bloch-type skyrmion. Moreover, we measure the magnetoresistance as a function of the applied field for MTD materials. In the in-plane field dependence of magnetoresistance and magnetization, we saw the clear corresponding jumps when the skyrmion is formed. |
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H71.00352: Nonmagnetic Zinc substitution on Cobalt Ferrites and measurement of their Structural, Dielectric and Magnetic Properties Tamanna Mariam, Kazi Hanium Maria, Nazrul Islam Khan, Shamima Choudhury A series of Co1-xZnxFe2O4 ferrites with (x=0.0,0.1,0.2,0.3,0.4,0.5) compositions were synthesized by standard double sintering ceramic technique. Substituting nonmagnetic Zn in place of Co influenced the structural, dielectric and magnetic properties of the samples. The X-Ray diffraction pattern confirmed the single-phase cubic spinel structure. The lattice parameters were found to increase with Zn substitution. The grain size of the samples was reduced by enhancing the Zn concentration. The dielectric constant of the sample is found to decrease with increase in frequency exhibiting normal dielectric behavior. The variation of the resistivity versus temperature was also studied and the dielectric constant of the system has a variation quite similar to that of the resistivity. Saturation magnetization and coercivity were estimated with variation of Zn content by VSM measurement. These effects are due to facilitation of demagnetization by substitution of the non-magnetic Zn ions. Permeability was found to decrease with increasing in Zn content, which showed proportionality behavior with grain size. Low coercivity, moderate saturation magnetization and high anisotropy constant has made Cobalt Ferrite a good candidate to contribute in multiferroic materials and in storage devices |
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H71.00353: Room-temperature ferromagnetism in oxidized-graphenic nanoplatelets induced by topographic defects John Prias, Katherine Gross, Hernando Ariza, Pedro Prieto, Cinzia Di Giorgio, Fabrizio Bobba, Annamaria Cucolo Pyrolytic oxidized-graphenic nanoplatelets (OGNP) obtained from bamboo pyroligneous acid (BPA) by varying the density of extended defects, show room-temperature ferromagnetism. Topographic defects, created during the fabrication process, arise from a natural formation of clusters; such clusters drastically distort the graphitic basal plane, giving rise to abrupt surface curvatures. Topographic defects were found to be sources of the magnetic signal, as evidenced by bulk magnetization and MFM measurements. Increased defect density, which is tuned by carbonization temperature, results in enhanced magnetization. |
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H71.00354: Self-regulating magnetic hyperthermia (SrMH) of NixCu1-x nanoparticles Bianca Paola Meneses Brassea, Mohamed F. Sanad, Dawn S. Blazer, Shirin Pourmiri, Ahmed A. El-Gendy NixCu1-x (x=0.2-0.5) nanoparticles have been synthesized by reducing Ni and Cu from metal precursors using sol-gel route followed by annealing at different temperatures for controlled self-regulating magnetic hyperthermia applications (SrMH). SEM, TEM, and XRD reveal spherical 20-50 nm nanoparticles with FCC cubic structure for different compositions of NixCu1-x. The magnetic properties exhibited ferromagnetic behavior with saturation magnetization (Ms) ranging from 8-20 emu/g at 300 K and Curie temperature ranging from 42-25 °C within the limit of the therapeutic temperature range of 42-46 °C. The feasibility of hyperthermia has been performed under the therapeutic limits of alternating magnetic field and frequency. The samples exhibited heating rate and a significant dissipated heating power or measured as specific absorption rate (SAR) ranging from 0.1-1.6 °C/min and 20-100 W/g, respectively. Results reveal nanoparticles' feasibility for self-regulating hyperthermia. |
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H71.00355: Functionalized superparamagnetic Fe@Au Core/shell nanoparticles and their feasibility for magnetic hyperthermia Bianca Paola Meneses Brassea, Mohamed F. Sanad, Dawn S. Blazer, Shirin Pourmiri, Ahmed A. El-Gendy Superparamagnetic Fe@Au core/shell nanoparticles have been synthesized at ambient condition at different ratios of Fe:Au precursors using one-step wet chemistry method and functinoalized with tween. SEM, TEM, and XRD reveal spherical FCC Fe core nanoparticles coated with Au shells. The particles sizes average 61, 71, 83 nm at Fe:Au precursor’s ratio of 1:1, 2:1, 3:2 respectively. VSM reveals superparamagnetic behavior at 300 K. The saturation magnetization (MS) of the samples amounts 79, 165 and 89 emu/g for 61, 71 and 83 nm respectively. Feasibility for hyperthermia treatment of cancer have been tested under applied magnetic fields and frequencies, heating power known as specific absorption rate (SAR) has been recorded. SAR dependence of magnetic field and frequency yields 35, 50, 25 W/g at therapeutic range of 400 Oe and 304 kHz for samples with MS of 79, 165 and 89 emu/g respectively. The samples show feasibility for future in vitro/in vivo studies for tumor cells. |
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H71.00356: The evolution of electronic and magnetic states for transition-metal rings embedded in carbon nanotubes Joseph Ward, Rithvi Ravichandran, Jason Haraldsen We investigate the electronic and magnetic states for various sizes of transition metal rings that have been substituted into carbon nanotubes. Using density functional theory, we examine the electronic density of states, magnetic moment, and total energy for various transition metal atoms and magnetic configurations. After determining the structural and magnetic ground states, we show how the introduction of these metal atoms affect the electronic states and determine the ground state magnetic configuration with a variation of transition metal atom and onsite potential. Future work will look into the use of these magnetic systems in a device application setting as we work towards possible spintronic applications. |
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H71.00357: Effect of Structural Disorder on the Magnetic Properties of Melt-Spun Co3+xV alloys Onur Tosun, Inci Ruzybayev, Frank M Abel, Balamurugan Balasubramanian, Ralph Skomski, David Sellmyer, George C Hadjipanayis We have investigated the structural and magnetic properties of melt-spun Co3+xV alloys for x = 0, 0.2, 0.4 and 0.6 in order to study the effect of structural disorder on the magnetic properties of Co-V alloys. Bulk Co3V exists in two phases: An ordered hexagonal (Al3Pu-type) low-temperature phase (LTP) and a cubic L12 (Cu3Au)-type high-temperature phase (HTP) [1, 2]. Both the LTP and HTP are paramagnetic down to 4.2 K. The as-spun samples have the HTP structure. However, when they are annealed at 1173 K, they transform into the LTP. Magnetic data suggest that the as-made ribbons are ferromagnetic with ordering temperatures of 10, 20, 30 and 75 K for x = 0, 0.2, 0.4 and 0.6, respectively. This behavior is attributed to a slight destruction of perfect order in the HTP and which can lead to an increase in the Co-Co exchange interaction. The magnetic properties of annealed samples are currently being measured and the results will be presented and discussed at the meeting. |
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H71.00358: Structural and Magnetic Properties of Iodide-Mediated Synthesized L12 FePt3 Nanoparticles Vimal Deepchand, Vasileios Tzitzios, George C Hadjipanayis Halide ion-mediated synthesis of L10 FePt has previously been used to form magnetically hard L10-FePt phase without the need of any post-annealing or 3rd element addition [1,2]. In this work, we chemically synthesized L12 FePt3 by the co-reduction of iron and platinum-based precursors in the presence of elemental iodine. Thermomagnetic data showed that the magnetic properties depend strongly on the degree of atomic ordering. The as-made structure showed the L12 phase but with a low degree of ordering. Magnetic measurements showed that the ordering temperature of the as-made sample is at 380 K. The chemical ordering increased to 0.71 when the samples were annealed at 700oC for 30 minutes. The annealed samples showed a different ordering temperature of 251 K. Our data agreed with those reported by Margeat et al [3]. Room temperature hysteresis loops showed that the coercivity of our samples increased with annealing temperatures, up to 0.23 kOe for samples annealed at 700oC. Thermomagnetic measurements from 50 K to 380 K also provide evidence of a phase transformation in the L12 FePt3 nanoparticles, which we believe to be the transition from the AFM state to a FM state. |
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H71.00359: Effect of Surfactants on the Shape of Iron Oxide Nanoparticles Synthesized by Thermal Decomposition Shirin Pourmiri, Vasileios Tzitzios, George C Hadjipanayis Superparamagnetic iron oxide nanoparticles are one of the most promising materials for biomedical applications. However, despite the large number of researches done on spherical nanoparticles, there is much less work on the effect of particle shape of these nanoparticles on their magnetic properties and biomedical applications. In this work, iron oxide nanoparticles were synthesized using thermal decomposition of iron acetylacetonate in the presence of a mixture of oleyl amine and oleic acid. The XRD measurements show that the nanoparticles have a pure Fe3O4 phase. TEM images show that by changing the ratio of oleic acid to oleyl amine from 0.6 to 1, 1.1 and 1.3 the nanoparticle’s shapes change from spheres to cubes, octopods and rods, respectively; when the ratio is increased to more than 1.3, the nanoparticles start to form spherical shape again. The size of each of these shapes can be precisely controlled by adjusting the time and temperature of the reaction. Magnetic properties and hyperthermia measurements of these samples will be presented and discussed in the meeting. |
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H71.00360: Characterization of NiFe/SiO2 multilayers for on-wafer inductors operating at radio and low GHz frequencies Sara Goldman Magnetic layers surrounding copper core inductors are studied for use in circuits operating at radio and low GHz frequency ranges in order to address performance issues and quality losses normally observed in miniaturized inductors. Coating an inductor core in a magnetic material has the potential to increase the inductance proportional to the magnetic permeability of the coating. The objective of this research is to identify and construct an appropriate magnetic coating to improve the inductance and quality (Q-factor) of inductors. Permalloy (Py) was selected for these experiments due to its high relative permeability. Py layers, from 10nm to 1μm thick, were grown on silicon wafers using magnetron sputtering. These layers were characterized with SQUID magnetometer and broad-band FMR system. A specific issue we address is that inductor coatings have the potential to decrease the Q-factor due to eddy currents during high frequency operation. A method to reduce eddy current losses is to reduce layer thickness. Therefore, in addition to individual Py layers, multilayer coatings are developed: depositing 5 to 50 identical layers of Py (for total thickness from 150nm to 1.5μm) separated with 5nm layers of SiO2. Such structures are suitable for high frequency inductor operations. |
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H71.00361: Mn2FeSi: Experimental realization of an antiferromagnetic inverse-Heusler alloy Dipanjan Mazumdar, Anil Aryal, Said A Bakkar, Hassana Samassekou, Sudip Pandey, Igor Dubenko, Shane Stadler, NAUSHAD ALI Search for low-moment magnetic materials with high spin-polarization is important for future spintronics applications. In this work, we have conducted detailed and varied materials growth and characterization along with complementary first-principles calculations to investigate the structure and magnetism of Mn2FeSi, which is a prospective inverse-Heusler material identified by prior calculations. We show that Mn2FeSi adopts a cubic structure that is in very good agreement with theoretical estimates while the magnetic and resistivity measurements show behavior consistent with antiferromagnetism which can be tuned to a very low-moment state under appropriate growth conditions. Supporting first-principles calculations show that compensated antiferromagnetic states are energetically feasible. Our work provides new evidence that the magnetic properties of Manganese-based inverse-Heuslers can be useful to explore new applications in the area of spintronics. |
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H71.00362: Emergent Topological Hall Effect in La0.7Sr0.3MnO3/SrIrO3 Heterostructures yao li, Lunyong Zhang, qinghua zhang, chen li, tieying yang, yu deng, lin gu, di wu Novel magnetic and electric phenomena could emerge in perovskite oxide heterostructures due to multiple and complex coupling at the hetero-interface. Here, we report that an emergent giant topological Hall effect (THE) can be induced in ferromagnetic La0.7Sr0.3MnO3 thin films in a wide temperature range up to 200 K by constructing La0.7Sr0.3MnO3/SrIrO3 epitaxial heterostructures. The observed THE indicates a non-coplanar spin texture, which also leads to strongly pinched field dependent magnetization (MH) loops in the out-of-plane direction. This THE and pinched MH loops are not observed in La0.7Sr0.3MnO3 single layer films or La0.7Sr0.3MnO3/SrTiO3/SrIrO3 trilayer heterostructures, indicating the relevance of the La0.7Sr0.3MnO3/SrIrO3 interface, where Dzyaloshinskii-Moriya interaction due to strong spin-orbital coupling in SrIrO3 may play a crucial role. This work demonstrates the feasibility of using SrIrO3 to modify magnetic and transport characteristics by interfacing with other correlated oxides, which might be useful to novel spintronic applications. |
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H71.00363: Novel Magnon Transport Properties in Magnetic Oxides by Mesoscopic Boltzmann Approach Yanxia Wang, Wei Wang, Yuheng Li, Jianwei Zhang The coherent transport properties of magnon in ferromagnetic insulator(FI) demand precise physical understanding of magnon scattering and relaxation processes. In this presentation, we invent a general magnon Boltzmann equation from full quantum magnon Hamiltonian[1]. By including N-process magnon-scattering due to dipole-dipole interaction, we demonstrated a novel collective decay dynamics of magnon group, which showed hydrodynamics transport properties of magnon. To conduct N-process scattering, a new spatial dependent magnon interaction field λ was introduced, which was describing collective local field in magnon. We also found N-process scattering is the physical origin that why coherence magnons can transfer to thermal magnons in FI relaxation process. Furthermore, our results showed magnon current can be manipulated by varying of anisotropy in magnetic oxides, especially in strong anisotropic energy materials, such as NiFe2O4 or CoFe2O4. In this framework, we also provide the methods to manipulate magnon transport by applying gradient magnetic field and gradient T field. |
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H71.00364: Two-dimensional magnetic monopole gas in an oxide heterostructure Ludi Miao, Yonghun Lee, Antonio B Mei, Michael J Lawler, Kyle M Shen Magnetic monopoles have been proposed as emergent quasiparticles in magnetically frustrated pyrochlore spin ice compounds, such as R2Ti2O7 (RTO) (R = Ho, Dy). To date, all experimental investigations have been limited to the behaviour of large ensembles comprised of equal numbers of monopoles and antimonopoles in macroscopic bulk. Therefore, fundamental questions about the existence, properties, and dynamics of single, isolated monopoles, as well as the new phases of matter that these monopoles may form, remain unanswered or inaccessible. To address these issues, we propose the formation of a two-dimensional magnetic monopole gas (2DMG) with a net magnetic charge and whose monopole density can be controlled by an external field, at the interface between a spin ice and an isostructural antiferromagnetic (AFM) pyrochlore iridate (e.g. R2Ir2O7 (RIO)). Our proposal is based on a series of Monte Carlo simulations of the thermodynamic and transport properties, which also demonstrate the robustness of the 2DMG against long-range dipolar interactions. This proposed 2DMG should enable entirely new classes of experiments and devices which can be performed on magnetic monopoles, akin to two-dimensional electron gases in semiconductor heterostructures. |
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H71.00365: Magnetic Properties of MBE Grown La1/3Y1/3Sr1/3MnO3 thin films and Superlattices Thomas Pekarek, Caitlin Kengle, James Payne, Dakota Brown, Maitri Warusawithana We have investigated the magnetic properties of thin films related to the standard CMR system La2/3Sr1/3MnO3 where Y substituted for 50% of the La atoms. These La1/3Y1/3Sr1/3MnO3 films were grown as a random alloy where La, Y, and Sr atoms randomly occupied the A-site or as a superlattice where each unit-cell-thick layer stacked along the crystallographic (001) direction contained only one of the atoms La, Y, and Sr occupying the A-site. One key magnetic feature of La2/3Sr1/3Mn03 is a prominent ferromagnetic transition near 350 K. We find the substitution of La with Y suppresses this ferromagnetic transition in both the random alloy and the superlattice samples. In the superlattice sample we find a magnetic transition that is coincident with a metal-to-insulator transition observed in electronic transport. In the random alloy sample, we see a similar magnetic transition but at lower temperatures, where we find the sample is too insulating to measure electronic transport. We will compare our measurements on these La1/3Y1/3Sr1/3MnO3 samples with CMR thin films of La2/3Sr1/3MnO3. |
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H71.00366: WITHDRAWN ABSTRACT
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H71.00367: Spin dynamics in a chain with three-spin interactions in a transverse magnetic field Osiel Bonfim, B Boechat, J. Florencio The quantum dynamics of a spin chain with three-spin interactions in the presence of a transverse magnetic field is investigated. We use both direct diagonalization and the method of recurrence relations to obtain the time-dependent correlation function and its corresponding frequency-dependent spectral density function. Although our calculations are done with chains up to 14 spins with periodic boundary conditions, the results are easily extended for infinite-size chains. We present the calculations for the behavior of these quantities as a function of the transverse magnetic field in the high-temperature limit. |
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H71.00368: Magnetic Properties and de Gennes Scaling of Quaternary Intermetallic Compounds wonchoon lee The interplay between antiferromagnetism and superconductivity has been studied for the quaternary intermetallic superconductor R1-xR’xNi2B2C systems from the isothermal magnetization curves and temperature dependent magnetization measurements to determine the crystalline field effect such as low energy levels of singlet Γ4 and excited Γ1 and Γ5 in theoretical group analysis of the energy scheme. In addition, by using the R+3 ions Hund’s rule, we have qualitative agreement between the de Gennes TN scaling behavior and crystalline electric effect scheme. |
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H71.00369: Reliable Electrical Switching of Tri-State Antiferromagnetic Néel Order in a-Fe2O3 Epitaxial Films Yang Cheng, Sisheng Yu, Menglin Zhu, Jinwoo Hwang, Fengyuan Yang Ability to manipulate antiferromagnetic (AF) moments is a key requirement for the emerging field of antiferromagnetic spintronics. Electrical switching of bi-state AF moments has been demonstrated in metallic AFs, CuMnAs and Mn2Au. Recently, current-induced “saw-tooth” shaped Hall resistance was reported in Pt/NiO bilayers, while its mechanism is under debate. Here, we report the first demonstration of convincing, non-decaying, step-like electrical switching of tri-state Néel order in Pt/a-Fe2O3 bilayers. Our experimental data shows the switching behavior of a-Fe2O3 Néel order among three stable states, which can be detected by the change of Hall resistance ΔRxy through spin Hall anomalous Hall effect (SH-AHE). We also show that the observed “saw-tooth” Hall resistance is due to an artifact of Pt, not AF switching, while the signature of AF switching is step-like Hall signals. Together with the Monte-Carlo simulations, we reveal the clear mechanism of AF Néel order switching and explain why only the first current pulse switches the Néel order. This demonstration of electrical control of magnetic moments in AF insulator (AFI) films will greatly expand the scope of AF spintronics by leveraging the large family of AFIs. |
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H71.00370: Large magnetic anisotropy in hexagonal Fe2MnSn alloy Yung Huh, Bishnu Dahal, Abdullah Al Maruf, Sam Prophet, Pavel Lukashev, Parashu R. Kharel We performed combined theoretical and experimental studies of electronic, magnetic, and structural properties of Fe2MnSn Heusler alloy. The density functional theory (DFT) calculations of bulk and thin-film Fe2MnSn Heusler alloys predict that this compound crystallizes in energetically close hexagonal D019 and cubic L21 phases due to their very similar equilibrium energies, which agrees well with the experimental results. Both the cubic and hexagonal phases are ferromagnetic with high Tc of 325 K and 475 K, respectively. The high-field magnetizations measured at 100 K are 3.3 µB/f.u. and 4.3 µB/f.u) for the cubic and hexagonal phases, respectively. These values are smaller than the predicted values (6.0 µB/f.u. for the cubic and 6.5 for the hexagonal phases) by the DFT calculations. The hexagonal phase shows high value of magnetic anisotropy of 5.1 Merg/cm3 at 100 K. The cubic phase has an energy gap in the minority-spin conduction band that vanishes in the hexagonal phase. |
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H71.00371: Study of magnetization dynamics in magnetic insulators for magnonic applications Rodrigo Victor, Luiz Sampaio, Flavio Garcia Electronics devices are based on semiconductors transistors, and their improvement is mostly due to reducing its size, which is reaching its limit. To overcome this problem magnonics have appeared as an alternative solution for electronics, with advantages such as lower energy cost, faster information exchange and lower heating due to the absence of Joule effect. Magnetic insulators, more specifically Y3Fe5O12 (YIG), appear as a promising material for this application because it has low Gilbert damping and low coercivity, among other properties. In this work, YIG thin films were reproducibly grown on Gd3Ga5O12 with 111 oriented substrates by magnetron sputtering furthermore an ex situ annealing with oxygen flow was performed. A systematic study of the magnetic dynamics using ferromagnetic resonance was carried out to optimize the growth conditions of YIG, seeking the lowest value of Gilbert damping aiming towards magnonic applications. After the optimization, non-magnetic metallic materials (bismuth-doped copper, which produces a giant spin Hall effect and Pt) were deposited on YIG to evaluate the applicability for the spin current generated by spin pumping and spin Hall effect via inverse spin Hall effect. |
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H71.00372: Direct light-induced spin transfer between different elements in a spintronic Heusler material via femtosecond laser excitation Christian Gentry, Phoebe M Tengdin, Adam Z Blonsky, Dmitriy Zusin, Michael Gerrity, Lukas Hellbruck, Moritz Hofherr, Justin Shaw, Yaroslav Kvashnin, Erna Delczeg-Czirjak, Monika Arora, Hans Nembach, Tom Silva, Benjamin Stadtmuller, Stefan Mathias, Martin Aeschlimann, Henry Kapteyn, Danny Thonig, Konstantinos Koumpouras, Olle Eriksson, Margaret Murnane Heusler compounds are exciting materials for future spintronics applications because they display a wide range of tunable electronic and magnetic interactions such as metallicity, superconductivity, and giant magneto-resistance. We use a femtosecond light pulse to directly transfer spin polarization from one element to another in a half-metallic Heusler material, Co2MnGe. This spin transfer initiates as soon as light is incident on the material, showing that we can transfer angular momentum between neighboring atomic sites on timescales less than 10 fs. The observation is made possible by the ability of ultrafast high harmonic pulses to simultaneously and independently probe the magnetic state at two atomic sites, Co and Mn, during laser excitation. We find that the magnetization of Co is enhanced by the laser pulse, while that of Mn rapidly quenches. By comparing our measurements to density functional theory, we show that the optical excitation directly transfers spin from one magnetic sub-lattice to another, via preferred spin-polarized excitation pathways. The enhancement of ferromagnetic order demonstrates direct manipulation of spins via light, thus providing a path towards spintronic devices such as switches that can operate on few femtosecond or faster timescales. |
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H71.00373: Finding Structural Phase Transitions in Barlowite and Claringbullite Alyssa Henderson, Lianyang Dong, Sananda Biswas, Hannah Revell, Yan Xin, John A Schlueter, Roser Valenti, Theo Siegrist Barlowite (Cu4(OH)6FBr) and claringbullite (Cu4(OH)6FCl) are minerals related to the quantum spin liquid candidate herbertsmithite ZnCu3(OH)6Cl2, the popular S = ½ antiferromagnet with a geometrically perfect kagome lattice. The kagome lattices of claringbullite and barlowite are stacked perfectly on top of one another, separated by planes consisting of Cu2+ and halide ions, and show promise as QSL candidates. Both materials have a hexagonal crystal structure with P63/mmc symmetry and undergo temperature-dependent phase transitions to Pnma symmetry1. Previously we examined the barlowite transitions at 276 K1, but the claringbullite transition occurs much lower. To pinpoint the transition, equipment had to be modeled and aligned. |
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H71.00374: Hanle effect in vertical Ohmic spin valves Yaroslaw Bazaliy Hanle effect measurements in lateral spin valves provide valuable information on spin lifetimes and diffusion lengths in the transport channel. However, their interpretation is made difficult by the fact that current distribution near the injector substantially deviates from the assumptions of a simple 1D model. These difficulties can be partially alleviated by using the "three terminal" measurement method. A logical continuation of this line of thought is the usage of a “current perpendicular to plane” (vertical) F/N/F spin valve, where electric current distribution is strictly uniform. Additional advantage of the vertical valve is a better experimental control of the normal spacer thickness. The complication is the presence of two F/N interfaces, both contributing to the total voltage drop. Here we derive theoretical expressions for the valve magnetoresistance due to Hanle effect experienced by spins in the normal spacer. We assume diffusive regime, transparent boundaries with Ohmic conductivity, and allow for the back-action of spin accumulation in N on the injection process. Magnetoresistance is calculated for arbitrary angle between the magnetizations of the F-layers and any thickness of the N-spacer. |
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H71.00375: Deterministic spin-orbit torque switching with a perpendicularly non-uniform magnet Seyed Armin Razavi, Hao Wu, Kang-Lung Wang Spin-orbit torque (SOT) switching of magnetization is a promising emerging technology for non-volatile memory and logic applications. However, deterministic switching of perpendicular magnetization with SOTs requires breaking of inversion-symmetry [1], usually provided by an external magnetic field, which is not suitable for practical applications. We experimentally realize deterministic SOT switching without any external magnetic fields by using a ferromagnet with non-uniform properties in the perpendicular direction (CoFe/CoFeB bilayer). In this structure, a heavy metal acts as the source of SOTs and all the layers have uniform thicknesses. We discuss the role of Dzyaloshinskii-Moriya interaction (DMI) as a possible cause of inversion-symmetry breaking. This method of symmetry breaking for SOT switching can be readily employed in current industrial processes and can pave the way for the practical application of SOT-based technology. |
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H71.00376: Effect of interfacial intermixing on spin-orbit torque in Co/Pt bilayers Giovanni Baez Flores, Kirill Belashchenko Using the first-principles non-equilibrium Green’s function technique [1] with supercell disorder averaging, we study the influence of interfacial intermixing on the spin-orbit torque in Co/Pt (111) bilayers. The interlayer distances are optimized, several models of intermixing are considered, and atomic potentials in the intermixed layers are obtained using the coherent potential approximation. The magnitude and thickness dependence of the damping-like torque are similar to earlier results for the Co/Pt (001) interface [1,2] and rather insensitive to intermixing. In contrast, the field-like torque, which is small in the case of an ideal interface, is dramatically enhanced by intermixing. |
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H71.00377: Giant magnetoelectric effect in Pt/Co/Ta ultrathin films with perpendicular magnetic anisotropy on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 ferroelectric substrate Aitian Chen, Haoliang Huang, Yan Wen, Senfu Zhang, Jürgen Kosel, Yalin Lu, Xixiang Zhang Perpendicular magnetic anisotropy (PMA) is important for increasing the information storage density in the perpendicular magnetic recording media, and electric-field control of PMA is drawing much attraction due to its potential to lower energy consumption. Multiferroic heterostructures, hybrid ferromagnetic and ferroelectric, enable electric-field control of magnetism via strain-mediated magnetoelectric coupling, though most studies have focused on how to control ferromagnetic films with in-plane magnetization. |
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H71.00378: Magnetic field noise caused by surface paramagnetic impurities on nitrogen vacancy center diamonds Philip Chrostoski, Deborah Santamore Noise is a detrimental issue for nitrogen vacancy (NV) center diamond sensing devices. The magnetic field noise is caused by both surface and bulk impurities. Here, we study the noise due to the interactions between the NV center electron spin and the surface impurity electron spins that are dissolved in a thin water layer on hydrogen (H-), oxygen (O-), or fluorine (F-) terminated surfaces. We apply the Langevin method to spin fluctuation theory to calculate and analyze the surface noise spectral density. Impurity hopping among the available sites determines the impurity relaxation time that controls the contribution of the noise either from the spin flip-flops noise only or additional spin precession noise. Our results show that O-terminated surface give a much lower surface noise than H- and F-terminated surfaces. This is because only spin flip-flop noise are present for O-terminated surface due to oxygen’s picosecond electron spin-lattice relaxation time while both spin flip-flop noise and spin precession noise are present for H- and F-terminated surfaces. Comparing to the previous work on bulk impurity noise, we find that the surface impurities are indeed a greater source of magnetic field noise than the bulk impurities. |
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H71.00379: Room temperature gate tunable spin-to-charge conversion in LaCrO3/SrTiO3 heterostructures Shijia Yang The emergence of novel spintronics studies focuses on the generation, transmission, and control of a pure spin current through spin-orbit effects. The emergence of novel electronic and magnetic phenomena at the interfaces between polar and non-polar crystalline transition metal complex oxides such as high mobility two-dimensional electron gases (2DEG) provides an ideal platform for the design of spin-to-charge (StC) convertors. At these interfaces, an interface-driven spin-orbit coupling mechanism - the Rashba effect - shows great promise due to its unprecedented StC interconversion efficiency, called inverse Rashba-Edelstein effect (IREE). We report a new type of 2DEG formed at the interface between antiferromagnetic LaCrO3 and insulating SrTiO3 heterostructure with StC conversion efficiency. The measured IREE length is up to 0.3 nm which can be modulated by a gate voltage. The frequency and field orientation dependence of IREE response are both consistent with the spin pumping model, from which the spin relaxation time (~30ps) is derived. Our findings launch a new class of oxide-based 2DEGs for future spin orbitronic applications. |
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H71.00380: Data-driven study of magnetic interactions of transition-metal based 2D materials Ayana Ghosh, Shizeng Lin, Jian-Xin Zhu Engineering magnetic interactions are critical to control magnetic behavior for device applications. Depending on the presence or absence of inversion symmetries, the magnetic interactions stabilize several exciting magnetic behaviors such as formation of chiral helimagnets, skyrmions, and even quantum spin liquid. Various exchange interactions and magnetic anisotropy within crystal lattices can be estimated using DFT-based simulations approaches, based on which an effective spin only Hamiltonian can be constructed. This multi-scale modeling allows one to predict magnetic properties for real materials. Here, we propose to use a data-driven approach to screen for suitable candidates exhibiting magnetic skyrmions, followed by evaluating their exchange interactions in transition-metal based 2D magnetic materials. This curated dataset of 2D magnetic materials and computed magnetic interactions can then be used to develop a combined protocol to search for similar compounds in a variety of materials space followed by constructing predictive machine learning models to understand magnetic behavior of such systems. |
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H71.00381: Study of Tunneling Magnetoresistance (TMR) in Twisted CrBr3 Bilayers Zhuangen Fu, Piumi Samarawickrama, Jifa Tian The recent discovery of two-dimensional (2D) magnetic materials (such as CrI3 and Cr2Ge2Te6) has opened new opportunities for novel electronics and spintronics [1][2]. By controlling the stacking angle between two monolayers, the twisted 2D bilayers have shown novel quantum states, such as unconventional superconductivity and ferromagnetism[3][4]. However, whether the magnetic ground states of twisted 2D magnetic bilayers can be tuned by the twisting angle is still an open question. In this work, we fabricated h-BN/Graphene/twisted CrBr3 bilayer/Graphene/h-BN devices using a dry-transfer technique with the twisting angle well controlled. The tunneling magnetoresistances of the twisted CrBr3 devices with different twisting angles will be measured at different temperatures and magnetic fields. We are aiming to establish a phase diagram of the magnetic ground states in the twisted CrBr3 bilayers as a function of the twisting angle. Our study may pave a new way for manipulating magnetic orders in 2D magnetic materials and offer new opportunities in designing 2D material-based spin devices. |
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H71.00382: First-principles calculations for high-temperature ferromagnetic semiconductor (In,Fe)Sb Hikari Shinya, Tetsuya Fukushima, Akira Masago, Kazunori Sato, Hiroshi Katayama-Yoshida Fe-doped semiconductors have been attracting much attention due to fascinating properties. In fact, Fe-doped InSb not only exhibits the high Curie temperature but can also be n-type doping [1]. Our previours calculations reveal that, (In,Fe)Sb has complex magnetic properties [2]. In the isoelectronic (In,Fe)Sb case, the Fe atoms show strong antiferromagnetic interactions due to the superexchange mechanism. We have demonstrated that by modulating the chemical potentials corresponding to n- or p-type doping, the magnetic property can be changed drastically from antiferromagnetism to ferromagnetism. This transition can be well understood in terms of the Alexander-Anderson-Moriya mechanism. However, we have obtained high Curie temperature in only p-type (In,Fe)Sb case. We suspect that there are the other ferromagnetic mechanisms in addition to the magnetic transition and spinodal nano-decomposition in (In,Fe)Sb. In this study, we have clarified the origin of high Curie temperature by the density functional theory calculations. |
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H71.00383: All-electron calculations of crystalline and amorphous phases in magnetic phase change materials by KKR Green's function method Tetsuya Fukushima, Kazunori Sato, Hiroshi Katayama-Yoshida, Rudolf Zeller, Peter Dederichs We perform large-scale density functional theory (DFT) calculations for crystalline and amorphous phases in magnetic phase change materials by all-electron full-potential screened Korringa-Kohn-Rostoker (KKR) Green’s function method. Here, we choose transition metals doped Ge2Sb2Te5 (GST) systems as the typical cases. We consider large unit cells containing 1000 sites for the crystalline phase and 1365 sites for the amorphous phase to model the configurational and structural disorders in the magnetic phase change materials. Such large-scale DFT calculations are performed using the program KKRnano, where a massively parallel linear scaling all-electron algorithm is implemented. We investigate the electronic structures and distance dependent magnetic exchange coupling constants in the crystalline and amorphous phases. It is found, in the crystalline phase, that ferromagnetic states are favorable in the cases of V and Cr doping, due to the double exchange mechanism, whereas antiferromagnetic superexchange interactions appear to be dominant for Fe- and Mn-doped GST. In particular, the Cr doped GST shows strong ferromagnetic interaction and high Curie temperature for both the crystalline and amorphous phases. |
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H71.00384: Interfacial Spin Conductance Behavior in Topologically Non-trivial Heterostructures Stephen Hofer, Trinanjan Datta, Dipanjan Mazumdar Spintronics is a paradigm that utilizes spin angular momentum as the fundamental logical bit for computing. Spin current is the means by which these bits can be altered to read and write digital information. Toward this end, topological magnon excitation offers a potentially alternative avenue to produce highly efficient topologically mediated spin currents in a device. Topological magnon excitations are hosted in 2D honeycomb topological magnon insulators (TMI) such as CrI3. We investigate the behavior of interfacial spin conductance at the boundary of TMIs, normal metals, and topologically trivial ferro- and anti-ferromagnets. The ensuing transport implications of the underlying topological heterostructure is discussed within the context of thermally driven spin conductivity. |
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H71.00385: WITHDRAWN ABSTRACT
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H71.00386: Growth and characterization of magnetic van der Waals films Alexander Bishop, Tiancong Zhu, Dante J O'Hara, Jay A Gupta, Roland Kawakami In the recent past, magnetic, two-dimensional (2D), van der Waals (vdW) systems have become an exciting class of materials to study. On their own, these materials can give insights to low-dimensional spin behavior, but they also have the potential to be integrated into vdW heterostructures. Both areas are rich in scientific novelty and potential spintronics applications. Here we present the synthesis and characterization of 2D vdW magnets 1T-MnSe2 and MnBi2Se4. The materials were grown by molecular beam epitaxy (MBE) and studied with various techniques including X-ray diffraction (XRD), spin-polarized scanning tunneling microscopy (SPSTM), and superconducting quantum interference device (SQUID). The XRD measurements show that highly crystalline MnBi2Se4 films can be grown consistently and SQUID measurements indicate a layered antiferromagnetic structure. This material also exhibits ferromagnetism in the monolayer limit with a Curie temperature near 10K. Monolayer 1T-MnSe2 exhibits room-temperature ferromagnetism when analyzed with SQUID measurements. The magnetic signal from this material was also directly observed using SPSTM with a chromium tip. |
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H71.00387: Magnetic phase transition of monolayer RuCl3 induced by optical and electrostatic unipolar doping Weiwei Gao, Yingzhen Tian, Erik Henriksen, James Chelikowsky, Li Yang RuCl3 is a layered material showing signatures of a quantum spin liquid and strong magnetic frustration. Based on first-principles calculations, we predict that electrostatic doping with either electrons or holes and optical doping can both cause a phase transition of free-standing monolayer RuCl3 from the spin-liquid phase to stable ferromagnetic ordering with a moderate carrier/e-h density, achievable with current experimental techniques. Increasing the electron-hole pair density by optical doping can further enhance ferromagnetism and also increases the Curie temperature significantly. The mechanisms for driving the magnetic phase transition of monolayer RuCl3 are discussed based on orbital magnetism and itinerant magnetism. Our prediction of optically driving 2D ferromagnetism offers the possibility of non-contact tunability for exploring new physics and spintronic applications. |
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H71.00388: Probing Chirality Induced Spin Selectivity in Chiral 2D Hybrid Perovskites Using Spin Hall Magnetoresistance Eric Vetter, Yan Liang, Yuzan Xiong, Shulei Zhang, Zhizhi Zhang, Yi Li, Hongwei Qu, Valentyn Novosad, Axel Hoffmann, Wei You, Wei Zhang, Dali Sun The emergence of the Chirality Induced Spin Selectivity (CISS) effect, where electron transport through chiral materials is spin filtered, offers many new and exciting opportunities for the field of spintronics. However, many questions surrounding the exact nature of this physical phenomenon still remain. Here, we employ spin Hall magnetoresistance (SHMR) measurements and use pure spin currents for probing the effective magnetic fields native to the chiral two-dimensional hybrid perovskites as predicted by the CISS effect. Chiral 2D perovskites are spin coated on top of Pt Hall bars on a Si/SiO2 substrate and the Pt resistance is measured using lock-in detection to separate the first and second harmonic dependencies as a function of magnetic field, field angle, and temperature. We find significant SHMR signals despite the lack of any ferromagnetic material, as well as exotic hysteretic behaviors that we attribute to a CISS-induced SHMR. This work helps to elucidate the mechanism of CISS and paves the way for the use of chiral hybrid perovskites for novel spintronic devices. |
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H71.00389: First-principles evaluation of four-fold symmetric component of anisotropic magnetoresistance in 3d transition metal alloys Yohei Kota Anisotropic magnetoresistance (AMR) is a conventional magnetotransport phenomenon, and its origin is understood based on the Campbell-Fert-Jaoul model. Recent experimental studies of AMR reported that the four-fold symmetric component of the electrical resistivity is not so small compared to the two-fold symmetric component in several material films. Theoretically, Kokado and Tsunoda proposed that the four-fold symmetric component of AMR is attributed to the degradation of the crystalline symmetry due to tetragonal distortion [1], whereas Yahagi, Miura, and Sakuma proposed that the four-fold symmetric component arises from the higher order contribution of spin-orbit interaction [2]. The both proposed mechanisms are possible, however, it is unclear which mechanism is more important to generate the four-fold symmetric component of AMR in a realistic material system. In this study, we simulate the magnetization angle dependence of the electrical resistivity in ferromagnets using first-principles calculations. We present the comparison of the two- and four-fold symmetric component of AMR in cubic and tetragonally distorted crystals. |
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H71.00390: Strain effects on the magnetotransport properties of transition metals Rafael Gonzalez-Hernandez, Jorge Amell, Alvaro Gonzalez-Garcia, William Lopez-Perez, Jairo Sinova The Anomalous Hall Effect (AHE) is a phenomenon which consists of an extra anomalous transverse voltage developing when current is passed through ferromagnetic material in a magnetic field. In this work, we studied the dependence of strain and magnetization effect on the intrinsic anomalous Hall conductivity (AHC) in 3d metal Fe-bcc, Co-fcc, Co-hcp, and FeCo structure. For the Fe-bcc case, the AHC shows a slightly decreasing with the increase of pressure, being this associate to the magnetization dependence with the lattice constant. However, the AHC for lattices constants above 2.95A shows a downturn around 70%, even when the magnetization has increased. This decreasing seems to be related to a transition of d-states occupations above this lattice constant. The computation of the anomalous Hall conductivity was carried out using ab-initio calculations (included the effect of spin-orbit interaction for the ferromagnetic state) and the Wannier interpolation technique for the application of the Kubo-Greenwood formula. |
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H71.00391: Topological magnons in the checkerboard lattice Antonio Pires In analogy with topological insulators in electronic systems, one has the topological magnon insulators which are characterized by the existence of edge states modes in the presence of a gap. In these systems one has a transverse heat current mediated by magnons in response to thermal gradient, or a transverse spin current in response to a magnetic field gradient. Here we study topological magnon effects in a generalized ferromagnetic checkerboard lattice, also known as planar pyrochlore, with Dzyaloshinskii-Moryia interaction (DMI). The DMI breaks the inverse symmetry of the lattice, generates a magnetic flux and leads to non zero Chern numbers. We calculate the Berry curvature, the spin Hall conductivity, the spin Nerst coefficient and the Hall thermal conductivity as a function of temperature. We also analyze the effect of an applied magnetic fiels. Our study complements work done in the honeycomb, kagome, Lieb and pyrochlore lattices. |
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H71.00392: Hopfion Dynamics in Chiral Magnets Zulfidin Khodzhaev, Emrah Turgut Resonant spin dynamics of topological spin textures are hugely correlated with their topological nature and can be employed to understand nature, which attracts interest in condensed matter physics and memory and storage technology [1]. Among topological spin textures, skyrmions and vortices have been heavily studied, but hopfions have been paid little attention thus far. In this study, we present a numerical resonant study of spin dynamics of a three-dimensional topological spin texture hopfion in a B20 chiral magnet. Recent studies proposed to use interfaces with strong perpendicular magnetic anisotropy adjacent to a B20 FeGe nanodisk to stabilize hopfions [2]. In our study, using micromagnetic simulations, we first identified the ground state spin configurations of a hopfion, effects of anisotropies, geometric confinements and demagnetizing fields. Then, we calculated the resonance frequencies and spin-wave modes of spin precession dynamics. Our work helps to guide experimental studies to identify 3-dimensional topological spin texture of hopfions in chiral magnets in a functioning device, where imaging is not possible. |
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H71.00393: Transportation of Topological Spin Textures at Material Boundaries Jeffrey Michel, Emrah Turgut We examine the dynamics of topological spin textures, magnetic skyrmions and skyrmionium, at the boundaries where material properties vary. Using skyrmions or skyrmionium as information storage, e.g race track memory, requires a basis of knowledge on how these topological spin structures react to changes in material parameters. Using micromagnetic simulations, we investigated the dependence of radius and Hall angle due to: exchange stiffness, magnetic saturation, Dzyaloshinskii–Moriya Interaction, damping constant, anisotropy, and non-adiabaticity of spin transfer torque. There is also a comparison made between the feasibility of skyrmionium as an alternative to skyrmions as a method of storing and transportation information. |
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H71.00394: Helimagnetism and Soliton Lattice in a Chiral Magnet Chenhui Zhang, Junwei Zhang, Peng Li, Ye Yuan, Senfu Zhang, Yan Wen, Dongxing Zheng, Xixiang Zhang Herein, we report the observation of helimagnetism and soliton lattice in a chiral magnet. Below the Curie temperature, the in-plane field-dependent magnetization shows an abrupt increase as well as a narrow hysteresis just before saturation, which indicates a metamagnetic transition from solition lattice to ferromagnetic state. Using Lorenz microscopy, we observed sinusoidal magnetic patterns in real space below the Curie temperature. In thin film samples, we also observed abrupt and hysteretic magnetoresistance jumps when sweeping the magnetic field. |
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H71.00395: A nonintrusive reduced order modelling of magnetic skyrmions Muhammet Annaorazov, Shady Ahmed, Omer San, Emrah Turgut We show that a nonintrusive reduced order modeling framework can predict the magnetic field dependent internal structures of magnetic skyrmions[1] and their density in thin films. After we train the framework using results of micromagnetic simulations, in which we vary the anisotropy, asymmetric exchange energy, and the external magnetic field, we were able to predict the ground state spin configurations for given anistorpy, asymmetric exchange energy, and external magnetic field. Besides, we implement PC[2] (principal component) manifold to interpolate multidimensional data more accurately compared to other methods. We then confirm these spin configurations by calculating micromagnetically[3] and found XX percent accuracy and XX orders of magnitude reduction in the simulation time. Our data-driven approach accelerates identifying the spin texture by eliminating the need of re-calculation of micromagnetic simulations for every material parameter in a functioning device. |
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H71.00396: Observation of skyrmion-like magnetism in multiferroic BiMnO3 Zong-Heng Yang, Hung-Cheng Wu, Ting-Wei Kuo, D. Chandrasekhar Kakarla, Liangzi Deng, Ching (Paul) W Chu, Hung-Duen Yang Polycrystalline sample BiMnO3 was synthesized at high-pressure and temperature and characterized by X-ray diffraction. In our previous reports [1, 2], the multiple magnetic anomalous transitions have been investigated under a hydrostatic pressure up to 11.9 kbar, where the interesting magnetic H-T phase diagrams were also established. In this study, we revisit the pressure effect on the magnetic properties in BiMnO3, particularly in low magnetic field region. Interestingly, a pressure induced skyrmion-like A phase was observed in low magnetic field. The striking and unexpected observation of skyrmion-like phase in BiMnO3 will be discussed. |
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H71.00397: Transport in a Spintronic Device Using a Magnetic Skyrmion Lattice David King, Jinke Tang, John Ackerman Magnetic skyrmions are a topologically protected state in certain magnetic systems. Their topological properties make skyrmions stable and thus a possible basis for memory or energy storage spintronic devices. We present results for a transport device that uses a skyrmion lattice in the magnetic insulator Cu2OSeO3 as a precursor to an energy storage device. Data from the transport device and its fabrication are presented. The transport data are then used to test the underlying elasticity theory for the skyrmion lattice. |
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H71.00398: GENERAL PHYSICS
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H71.00399: Effect of viscosity on propagation of MHD waves in astrophysical plasma Alemayehu Cherkos
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H71.00400: Unification of Gravity and Electromagnetism Mohammed El-Lakany Gravity and electromagnetism are two sides of the same coin, which is the clue of this unification. Gravity and |
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H71.00401: Adding a Dynamic to Gravitation Reveals How Extra Gravity Halos are Projected from Galactic Cores John Huenefeld It is unfortunate that the term dark matter was used to describe the extra gravity observed in galaxy clusters. The name presupposes a material answer, but the only thing actually observed is an Extra Gravity Halo (EGH). The mysterious source of this extra gravity remains unresolved. Or does it? |
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H71.00402: Excess Surface Energy and Attraction of Matter: A New Vision to explain the Origin of Gravitation Pritam Mandal This talk presents a model based on minimization of excess surface energy to better explain the origin of gravitation, which is more intuitive and coherent with other fundamental principles of the working of the physical world. Here’s a picture to imagine: If a big ball of liquid (say water or mercury) is broken into many pieces, and kept on a frictionless plane in vacuum (say in an enclosed glass-jar), the smaller balls would tend to merge back into a single ball (initial state). An observer watching the phenomena from outside the glass-jar would explain the phenomena in terms of some mysterious force (e.g. gravitation), but the merging of the smaller balls in this ideal experimental set-up is merely an outcome of the tendency of the universe to minimize free energy. Surface tension explains this phenomenon satisfactorily. For same reason, metallic surfaces touching in the vacuum can stick to each other and fuse, known as the cold welding. |
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H71.00403: Statistical Analysis of Low States in VY Scl Stars Kylee Ford, Frederick A Ringwald The first detailed statistics of the light curves of a class of cataclysmic variable binary star systems, known as the VY Sculptoris stars, was compiled. These light curves are time-series observations of these stars’ apparent magnitudes in visible light. These observations were made by the American Association of Variable Star Observers and were made available publicly on a server funded by the National Science Foundation. In every star in this sample, the presence of low states that define the VY Scl stars was confirmed. The VY Scl stars typically spend most of their time in a high state, and irregularly drop by between 0.4 and 7.6 magnitudes into low states. We have compiled tables of the depths and durations of the low states of each system. We discuss these statistics in the context of the explanation that the low states may be caused by concentrations of magnetism on the secondary star, namely starspots. |
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H71.00404: Sea water intrusion in coastal aquifers and sustainable solution to control the intrusion Libia Hazra, N. Srinivas, Ch. Ramakrishna Groundwater in coastal regions is often prone to degradation in quality due to sea water intrusion. Sea level rise, coastal geomorphology, the amplitude and frequency of water waves, the depth of water near the coast, changing precipitation regimes and changing groundwater recharge rates may all influence the incidence of saltwater intrusion. A systematic study has been carried out to evaluate salt water intrusion in the coastal aquifers of Visakhapatnam city, Andhra Pradesh, India. The study areas are alongside of the sea (Bay of Bengal) shore. Water samples from bore wells were analyzed to determine the physico-chemical parameters of groundwater. Presence of bromide in all samples and Cl/Br ratio confirms the seawater intrusion near seashore samples. This condition is attributed to anthropogenic activities of the respective area and also the influence of climate conditions over Bay of Bengal. |
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H71.00405: Ferromagnetism in the hexagonal cage-like compounds Sm6(Mo,W)4Al43 juan mejia marin
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H71.00406: Au nanoparticle’s plasmonic nearfield induced photoluminescence enhancement of fluorophores Hasna Alali Gold nanoparticles in fused quartz substrates were synthesized with ion implantation using the Western Michigan University’s particle accelerator lab. Localized Surface Plasmon Resonance with respect to ion fluence (1 x1016 to 9x1016 atoms/ cm2) at fixed ion beam energy (70 keV) was studied. Rutherford Backscattering Spectrometry and UV/Vis techniques were used to quantify Au concentration and detect the formed nanoparticles respectively within the substrate. The investigation of enhanced electric fields of embedded nanoparticles with incident electromagnetic wave were used to amplify the photoluminescence intensity of dye and various perovskites nanocomposites. Steady state time resolved photoluminescence spectroscopy were used to investigate the emission enhancement and the energy transfer between the fluorophore and the metal nanoparticle. It was observed that the photoluminescence enhancement of perovskites in the vicinity of Au nanoparticles had a direct relationship with the ion implanted fluence. The photoluminescence intensity was quenched for C515 dye indicating the energy transfer from molecule to the Au nanoparticle. The photoluminescence enhancement was obtained for the lead halide perovskites and the maximum relative enhancement of ~29 times was obtained in CsPbI3. |
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H71.00407: Discovery of Faraday’s law of self-induction Junho Jeong Maxwell mathematically proved electromagnetic wave emission via his wave equations, and Hertz proved it experimentally. However, Hertz experimented on Henry’s self-induction instead of mutual-induction. An oscillating electric dipole p(t)=Q(t)r with charge Q(t) emits electric dipole radiation because of the external energy, and Faraday’s law shows the relationship between the two charges. Here, we have first discovered the existence of a new Faraday’s law of self-induction, which only requires charge Q(t) and that an electromagnetic wave is a method of emitting the received external energy for Q(t) to return to the stable state according to Lenz’s law. Second, when the inapplicability of relativistic electromagnetism to the Lorentz force was analysed based on the above facts, we additionally discovered that observers in different inertial systems could physically distinguish charges generating electric fields from those generating magnetic fields because the physical phenomena between the perspectives of mass and charge differ. |
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H71.00408: Advances and possibilities of the Materials Innovation Platform with examples from Spin-ARPES Daniel Beaton, M. Lundwall, T. Weill The quest for device applications based on quantum materials, such as topological insulators or superconductors, requires strict control of the environments these materials are exposed to during production and while under investigation. It is therefore most straightforward to gather all parts of the experiment, from sample growth to analysis, in one connected UHV system - creating a so-called Materials Innovation Platform (MIP). This approach has proven to be extraordinarily valuable in recent years. |
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H71.00409: Probing Dark Matter Halos with Ultra-Faint Dwarf Galaxies: A Spectroscopic Analysis of Leo V Sydney Jenkins, Ting Li, Joshua A Frieman The nature of dark matter presents one of the most significant problems in astrophysics. Ultra-faint dwarf (UFD) galaxies may play a key role in solving this mystery, as they are the most dark-matter dominated systems known and they allow us to probe dark matter halos down to the scale of tens of parsecs. However, many UFDs have few known member stars, making it difficult to provide robust measurements of the galaxies’ key features. We are currently locating new members and providing refined, consistent measurements of physical parameters for 15 UFDs using publicly archived spectroscopic data from the Very Large Telescope. We present a representative analysis of Leo V, a UFD with twelve known non-variable member stars. We identify three new likely members in addition to five new plausible members that require further follow-up, and perform a comparative analysis of seven previously discovered members. Using our catalogue of member stars, we perform a search for binary stars within the galaxy and investigate the possibility that Leo V is tidally disrupted. Our analysis of Leo V and other UFDs will enhance our understanding of these enigmatic stellar populations and contribute to future dark matter studies. |
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H71.00410: Casimir Energy For Perfect Electric Conductors Using the A-Phi Formulation Carlos Salazar-Lazaro Previous work by Reid, et.al. [1] calculated the Casimir energy for conducting geometries using the method of moments applied to the impedance matrix given by Electric Field Integral Equation (EFIE). His results were later extended by Atkins [2] by making use of the Argument Principle applied to the EFIE and transforming the calculation of the Casimir energy to one that used the Augmented EFIE (AEFIE) as its impedance matrix. We will use the same approach as Atkins but instead of using the AEFIE, we will propose using the A-Phi [3] formulation impedance matrix in order to calculate the Casimir energy for 2-D conducting geometries. |
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H71.00411: Tricritical physics in two-dimensional p-wave superfluids near resonance Fan Yang, Fei Zhou We study the effect of quantum fluctuations on the stability of two-dimensional (p+ip)-wave superfluids near resonance. The system is a Bardeen-Cooper-Schrieffer superfluid on one side of the resonance and a Bose-Einstein condensate on the other side. When the quantum fluctuations are strong, the interactions between Cooper pairs or bosonic molecules are substantially renormalized. As a result, the interactions between bosonic fields can become attractive at low energy and destabilize the superfluid phase even if the mean-field interactions are repulsive. We find that in the strong coupling limit, there exists a finite region near resonance where the superfluids are unstable and the system undergoes a first order phase transition at its boundary. The size of this region scales as exp(-c/g2), where g is the p-wave interaction constant and c is a numerical factor. Using a simple renormalization group analysis, we identify the tri-critical points which separate the continuous phase transition from the first order phase transition. |
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H71.00412: Electron correlation Time-Dependent Density-Functional Theory for Higher Harmonic generation in solids Didarul Alam, Naseem Ud Din, Shima Gholam Mirzaeimoghadar, Tao Jiang, Michael Chini, Volodymyr Turkowski We present details of our Time-Dependent Density-Functional Theory (TDDFT) approach, which takes into account the effects of electron-electron correlations, to analyze high-order harmonic (HH) spectra in solids. The used TDDFT exchange-correlation kernel was obtained from the charge susceptibility for the effective Hubbard model for the system calculated by using Dynamical Mean-Field Theory. The corresponding system of the TDDFT equations for polarizations and state occupancies is a generalization of the semiconductor Bloch equations on the case of locally-interacting electrons. To establish the signs of the correlation effects in the HH spectrum, we solved the equations analytically in the limit of weak external laser-pulse perturbation and numerically for various field strengths in the case of one of the most studied system – ZnO. It was found that correlation effects significantly affect the HH spectrum, most notably by shifting the spectral weight to higher harmonics. We discuss possible extensions of the theory on the case of non-local electron-electron interactions. |
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H71.00413: Hot electron noise in semiconductors from first principles Peishi Cheng, Alexander Choi, Austin Minnich First principles calculations of the properties such as mobility in semiconductors are now routine owing to advances in the ab-initio treatment of the electron-phonon interaction. However, fluctuational properties like the spectral noise power of current fluctuations, which can be calculated from the same ab-initio inputs, are experimentally accessible but yet to be reported. Here, we report an ab initio calculation of the spectral noise power in GaAs using a Boltzmann-Green’s function method. This approach expresses the noise spectral power using the current autocorrelation function computed from solutions of the Boltzmann transport equation with first principles electron-phonon interactions as input. The physical insights yielded by this description of fluctuational properties will help guide the design of semiconductor devices operating closer to the standard quantum limit of noise. |
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H71.00414: Consecutive Study Of Back Contact Barrier Height and CdS Layer Thickness And Their Effect On CdTe Solar Cell Efficiency Patrick Milan, Matthew Melfi, Yunis Yilmaz, Sade Sampson, Mehmet Alper Sahiner, Prof Weining Wang Favored for its low cost and relatively high efficiency (22.1% in 2016), Cadmium Telluride (CdTe) solar cells are popular among the thin film generation because they still have room for improvement. CdTe solar cells have a high electron affinity (about 4.5 eV) and as a result when metal contacts are used, a good ohmic contact is not created, and a Schottky barrier is formed at the back-contact junction. This barrier impedes current flow and lowers cell performance. The thickness ratio of Cadmium Sulfide (CdS) to CdTe is also important as increasing or decreasing the thickness of the [n-type] CdS layer will affect the production and recombination rate of charge carriers. |
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H71.00415: Non-volatile nanosecond phase change in BiFeO3 thin films induced by pulse laser Yi-De Liou, Haili Song, Wen-Yen Tzeng, Rong Huang, Chih-Wei Luo, Yi-Chun Chen, Jan-Chi Yang, Yu Chen Liu Nowadays, increasing technology interest has focused on the optical control of non-volatile functional units based on ferroic materials, especially those with ultrafast tunabilities. Despite the fact that various light sources can be used to alter the ferroelectricity and magnetization of ferromagnets via means of light, this usually requires low-temperature or high-energy flux to fulfill significant changes. In this work, we reveal nanosecond non-volatile phase alteration in multiferroic BiFeO3 (BFO) thin films. |
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H71.00416: Investigation of self-heating phenomena in high-electron mobility transistors (HEMTs) using millisecond-resolution Y-factor method Alexander Choi, Austin Minnich Low noise microwave amplifiers are critical components in measurement systems with applications ranging from qubit readout in quantum computing to the detection of fast radio bursts in RF astronomy. Recent work has suggested that the noise floor in high electron mobility transistors (HEMTs), presently around a factor of 5 above the quantum limit, is in part set by the thermal noise from the gate metal corresponding to a temperature exceeding the cryostat temperature. This temperature differential originates from high thermal resistance associated with phonon blackbody radiation at cryogenic temperatures. In this talk, we report on experiments designed to examine self-heating phenomena in HEMTs at cryogenic temperatures using liquid helium cooling and a custom noise figure analyzer that measures noise temperature with millisecond resolution. Our results confirm that self-heating at cryogenic temperatures is key mechanism in setting the noise floor of transistor amplifiers. These findings help to identify a path for transistor microwave amplifiers operating closer to the standard quantum limit of noise. |
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H71.00417: Design of Polyelectrolyte-based Materials using Molecular Modeling Thomas Oweida, Ibrahim Ahmad, Yaroslava Yingling Polyelectrolyte block copolymers have shown promise as carriers for drug and gene delivery due to their ability to self-assemble into a variety of responsive morphologies with tailored properties. Dissipative Particle Dynamics (DPD) is a computationally inexpensive, coarse-grained simulation technique that has previously been used to predict the resulting morphologies of polyelectrolyte block copolymers. However, the design space of these materials is still largely unexplored with the influence of most design parameters being poorly understood. This study utilizes DPD and machine learning methods to investigate a multi-dimensional, morphological phase diagram for polyelectrolyte block copolymers. A machine leaning method, support vector machine (SVM), is trained and tested on DPD simulation data to handle the high dimension of features influencing the polyelectrolyte block copolymer morphology. The results are the development of a comprehensive and detailed morphological phase diagrams for block copolymer properties versus environmental conditions that can be used as a robust predictive tool. These results provide the fundamental basis for synthesizing polyelectrolyte block copolymers for materials with novel, desirable properties. |
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H71.00418: Jammed solids held together with pins: structure and dynamics Liam Packer, Brian Jenike, Ari Liloia, Amy Graves, Sean Ridout Currently, much is known about idealized grains like soft discs in the vicinity of the "Point J" threshold for jamming. However, an important unanswered question concerns the role that a scaffolding in the form of fixed particles, or "pins", plays in the structure and dynamics of a jammed solid. We model pins as tiny fixed particles organized in lattice shapes such as square, triangular, honeycomb, or randomly distributed lattices. We find a number of interesting results: While at low pin densities the jamming threshold, φj, does what one expects - decreases linearly with pin density and independently of pin geometry - this is not true in general. Instead, the behavior of φj with pin density depends on the type of lattice, and whether the particles are bi- or polydisperse. The distribution of contact forces is very different from the familiar gaussian shape in the absence of pins. The linear elastic response is significantly affected by pins, both in terms of the magnitudes of bulk and shear moduli and the Zener ratio, showing that pins can break the isotropy of jammed states. |
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H71.00419: Adsorption of Binary Gas Mixtures on Graphite G.M Dinuka Gallaba, Aldo Dante Migone Determining how a binary gas mixture approaches equilibrium in the presence of a sorbent can have important implications for applications adsorption to gas separation. To understand the behavior of binary gas mixtures we are studying how adsorption equilibrium is reached on a well characterized planar sorbent, exfoliated graphite. We have conducted a series of adsorption measurements of methane and nitrogen mixtures on exfoliated graphite at low temperatures. We will present results for different initial mixture compositions and different temperatures. We will present results on the how the pressure approaches equilibrium, and, on the composition of the mixture at equilibrium for the different conditions explored. |
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H71.00420: Solving the Green's function as a single eigenstate in a boundary value problem Jose Hernandez, Li Ge It is well known that the Green’s function of an operator L(x) in a boundary value problem can be expressed as a bilinear expansion using the eigenstates of L(x). Here we introduce an auxiliary eigenvalue problem, from which the Green’s function is uniquely determined by a single eigenstate. This approach is easy to implement numerically, and it becomes very helpful when the eigenstates of L(x) are badly conditioned, for example, when L(x) is non-Hermitian and at an exceptional point. We illustrate this approach in one-dimensional and two-dimensional Helmholtz equations, with a focus on non-Hermitian systems that are due to their openness as well as non-Hermitian potentials. |
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