Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session U71: Poster Session III (2:00pm - 4:00pm)On Demand Poster Undergrad Friendly
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U71.00001: CONDENSED MATTER PHYSICS
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U71.00002: Wannier band transitions in disordered pi-flux ladders Jahan Claes, Taylor L Hughes Boundary obstructed topological insulators are an unusual class of higher-order topological insulators with topological characteristics determined by the so-called Wannier bands. Boundary obstructed phases can harbor hinge/corner modes, but these modes can often be destabilized by a phase transition on the boundary instead of the bulk. While there has been much work on the stability of topological insulators in the presence disorder, the topology of a disordered Wannier band, and disorder-induced Wannier transitions have not been extensively studied. In this talk, we explore the effect of disorder on the simplest example of a Wannier topological insulator: a mirror-symmetric pi-flux ladder in 1D. We demonstrate that the Wannier topology is robust to disorder, and establish a connection between the Wannier topology and the energy band topology of a system with a physical boundary cut, something which has generally been conjectured for clean models, but has not been studied in the presence of disorder. These results suggest that Wannier topology can be a powerful tool for studying the boundaries of disordered BOTIs. |
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U71.00003: Specifc boundary conditions and enhanced transmission in a dice lattice under
linearly polarized dressing field Andrii Iurov, Liubov Zhemchuzhna, Paula Fekete, Godfrey Anthony Gumbs, Danhong Huang We have investigated electron tunneling for a dice lattice in the presence of linearly polarized external dressing fied. Linearly polarized irradiation leads to a finite anisotropy of the Dirac energy dispersion relations of the investigated material, and a specific type of the wave functions for the dressed electron states. The direction of the light polarization can be generally different from the direction of incoming electrons. Such a finite misalignment angle together with the dispersion |
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U71.00004: Analytical solution to the surface states of antiferromagnetic topological insulator MnBi2Te4 Hai-Peng Sun, C. M. Wang, Song-Bo Zhang, Rui Chen, Hai-Zhou Lu, X. C. Xie The intrinsic magnetic topological insulator MnBi2Te4 has an out-of-plane antiferromagnetic order, which is believed to open a sizable energy gap in the surface states. This gap, however, was not always observable in the latest ARPES experiments. To address this issue, we analytically derive an effective model for the 2D surface states by starting from a 3D Hamiltonian for bulk MnBi2Te4 and considering the spatial profile of the bulk magnetization. We suggest that the Bi antisite defects in the Mn atomic layers in the bulk may be one of the reasons for the varied experimental results, since the Bi antisite defects may result in a much smaller and more localized intralayer ferromagnetic order, leading to the diminished surface gap. In addition, we calculate the spatial distribution and penetration depth of the surface states, which are mainly embedded in the first two septuple layers from the terminating surface. From our analytical results, the influence of the bulk parameters on the surface states can be found explicitly. Furthermore, we derive a k.p model for MnBi2Te4 thin films and show the oscillation of the Chern number between odd and even septuple layers. Our results will be helpful for the ongoing explorations of the MnBixTey family. |
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U71.00005: Transverse Thermoelectric Transport in Polycrystalline NbP Katherine Schlaak, Eleanor F. Scott, Chenguang Fu, Safa Khodabakhsh, Satya N. Guin, Ashley E. Paz y Puente, Claudia Felser, Sarah Watzman
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U71.00006: Magnetotransport Phenomena in Bi2Se3 Thin Films and FIB-Patterned Single Crystals Rubén Gracia-Abad, Soraya Sangiao, Chiara Bigi, Sandeep Kumar Chaluvadi, Pasquale Orgiani, Geetha Balakrishnan, JOSE MARIA DE TERESA NOGUERAS Topological Insulators (TIs) have emerged as a novel class of quantum materials predicted to possess an insulating bulk and spin-momentum locked metallic states at the surface produced by a non-trivial topology of the band structure. Bi2Se3 is one of the most studied materials in the field, due to its relatively large band gap of 0.3 eV and its simple surface band structure consisting of a single and well-defined Dirac cone. |
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U71.00007: Excited quantum anomalous (spin) Hall effect: enantiomorphic flat bands in a diatomic Kagome lattice Yinong Zhou, Gurjyot Sethi, Hang Liu, Zhengfei Wang, Feng Liu Quantum anomalous Hall effect (QAHE) and quantum spin Hall effect (QSHE) are ground-state equilibrium properties characterized by Fermi level lying in a topological gap, below which all the occupied bands are summed to a non-zero Chern and Z2 number for the QAHE and QSHE, respectively. Here, we propose theoretical concepts and models of non-equilibrium excited-state QAHE (EQAHE) and QSHE (EQSHE) generated by photoexcited singlet and triplet excitonic states, respectively, between two enantiomorphic flat bands (FBs) of opposite chirality hosted in a diatomic Kagome lattice. The two FBs have a trivial gap in between, i.e., the system is a trivial insulator in the ground-state; but nontrivial gaps above and below, so that upon excitation, the quasi-Fermi levels of both electrons and holes will lie in a nontrivial gap, when complete population inversion is achieved as in an excitonic insulator. Then dissociation of singlet and triplet excitons will lead to EQAHE and EQSHE, respectively, with the former breaking and the latter preserving the time-reversal symmetry. Implications and realization of enantiomorphic FBs in real materials are also discussed. |
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U71.00008: Probing Spin Liquid Phases in the Kitaev Honeycomb Model using Hierarchical Mean-Field Theory Daniel Huerga, William Holdhusen, Gerardo Ortiz Hierarchical mean-field theory (HMFT) identifies relevant cluster degrees of freedom while preserving all symmetries of the full model Hamiltonian, thus dealing with competing orders on an equal footing. This approach has been successfully applied to frustrated quantum spin and bosonic systems. A question remains: How reliable is the method when applied to models displaying phases with topological quantum order? Using the HMFT we recover an accurate phase diagram of the exactly-solvable Kitaev Honeycomb model, which is one of the paradigmatic 2D models hosting quantum spin liquid phases. This constitutes an excellent starting point to explore other potential spin-liquid phases occurring when magnetic field and additional interactions are added to the model. |
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U71.00009: Field-free platform for Majorana-like zero mode in superconductors with a topological surface state Qi Zhang, Songtian Sonia Zhang, Jiaxin Yin, Guoqing Chang, Tay-Rong Chang, Kun Jiang, Changqing Jin, Raman Sankar, Zahid Hasan Superconducting materials exhibiting topological properties are emerging as an exciting platform to realize fundamentally new excitations from topological quantum states of matter. In this letter, we explore the possibility of a field-free platform for generating Majorana zero energy excitations by depositing magnetic Fe impurities on the surface of candidate topological superconductors, LiFeAs and PbTaSe2. We use scanning tunneling microscopy to probe localized states induced at the Fe adatoms on the atomic scale and at sub-Kelvin temperatures. |
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U71.00010: Corroborating the bulk-edge correspondence in weakly interacting one-dimensional topological insulators Antonio Zegarra, Denis R Candido, Carlos Egues, Wei Chen We present a Green’s function formalism to investigate the topological properties of weakly interacting one-dimensional topological insulators, including the bulk-edge correspondence and the quantum criticality near topological phase transitions, and using the interacting Su-Schrieffer-Heeger model as an example. From the many-body spectral function, we find that closing of the bulk gap remains a defining feature even if the topological phase transition is driven by interactions. The existence of edge state in the presence of interactions can be captured by means of a T-matrix formalism combined with Dyson’s equation, and the bulk-edge correspondence is shown to be satisfied even in the presence of interactions. The critical exponent of the edge state decay length is shown to be affiliated with the same universality class as the noninteracting limit. |
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U71.00011: First-principles study of the nontrivial topological phase in chains of 3d transition metals deposited at superconducting surface Aksel Kobialka, Przemyslaw Piekarz, Andrzej Oles, Andrzej Ptok Recent experiments have shown the signatures of Majorana bound states at the ends of magnetic chains deposited on a superconducting substrate [1,2]. Here, we employ first-principles calculations to directly investigate the topological properties of 3d transition metal nanochains (i.e., Mn, Cr, Fe, and Co). In contrast to the previous studies, we found the exact tight-binding models in the Wannier orbital basis for the isolated chains aswell as for the surface-deposited wires. Based on these models, we calculate the topological invariant for all systems. For the isolated chains we demonstrate the existence of the topological phase only in Mn and Co systems. Next, we showed that a coupling between the chain and substrate leads to strong modification of the band structure. Moreover, the analysis of the topological invariant indicates the possibility of emergence of the topological phase in all studied nanochains deposited on the Pb surface. Therefore, our results demonstrate an important role of the coupling between deposited atoms and a substrate for topological properties of nanosystems, that should be implemented in future studies [3]. |
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U71.00012: Chiral Majorana modes and nodal loops in a periodically driven Kitaev model Paolo Molignini, Wei Chen, Chitra Ramasubramanian The paradigmatic Kitaev model on the honeycomb lattice is known for hosting nondispersive Majorana edge modes. We investigate the system when the couplings are periodically driven in time with a three-step protocol. By analyzing the quasienergy spectra for different edge geometries, we discover a rich interplay of different topological states: nondispersive and chiral Majorana edge modes, corner modes, and nodal loop gap closures. The chiral Majorana 0 and pi modes are induced by the time-reversal symmetry breaking caused by the drive. However, we discover that at a sweet spot of the driving intensity the system experiences frozen dynamics and concomitantly undergoes a topological phase transition to a nodal loop semimetal phase, belonging to its own unique universality class. At the line of frozen dynamics, effective time-reversal and mirror symmetries re-emerge and the corresponding nondispersive Majorana modes are reinstated. Our protocol thus provides a Floquet-engineered route to time-reversal symmetry breaking and tuning for the generation and control of chiral Majorana modes without the need for magnetic fields. |
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U71.00013: Impurity scattering in the Kitaev chain and its effect on odd-frequency spin-triplet pairing. Sparsh Mishra, Shun Tamura, Akito Kobayashi, Yukio Tanaka The Kitaev chain is the simplest model of topological superconductors hosting Majorana fermions that appear as zero-energy states at the edges. Its presence is linked to the emergence of odd-frequency pairing. We investigate the effect of an impurity in the Kitaev chain and study its impact on the odd-frequency spin-triplet pairing. We use a scattering approach to obtain the Green’s function of the semi-infinite Kitaev chain with a delta-function-type impurity potential within the quasi-classical regime analytically [1] and analyze the spatial dependence of the zero-energy LDOS and low-frequency odd-frequency component. |
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U71.00014: Anomalous proximity effect for d-wave superconductor with Rashba spin-orbit interaction Shun Tamura, Yukio Tanaka In the usual case, the local density of states (LDOS) in a diffusive normal metal (DN) for DN-superconductor junction is almost constant as a function of energy due to scattering in the DN. On the other hand, for DN-p-wave superconductor junction, zero energy peak for the LDOS in the DN is expected due to penetration of odd-frequency spin-triplet s-wave Cooper pair amplitude, and this phenomena is called an anomalous proximity effect. The anomalous proximity effect is theoretically predicted but has not been observed yet because of the lack of candidate materials. We study a DN-d-wave superconductor with Rashba spin-orbit interaction junction[1]. In the absence of Rashba spin-orbit interaction, the anomalous proximity effect does not occur. Rashba spin-orbit interaction generates odd-frequency spin-triplet s-wave pairing at the interface which is robust against impurity scattering and we found this system shows the anomalous proximity effect. |
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U71.00015: Floquet vortex states induced by light carrying the orbital angular momentum Hwanmun Kim, Iman Ahmadabadi, Hossein Dehghani, Ivar Martin, Mohammad Hafezi We propose a scheme to create an electronic Floquet vortex state by irradiating the circularly-polarized laser light carrying non-zero orbital angular momentum on the two-dimensional semiconductor. We study the properties of the Floquet vortex states analytically and numerically using methods analogous to the techniques used for the analysis of superconducting vortex states, while we exhibit that the Floquet vortex created in the current system has the wider tunability. To illustrate the impact of such tunability in quantum engineering, we demonstrate how these vortex state can be used for quantum information processing. |
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U71.00016: Transport in topological surface-states emerging from an interplay between isotropic and anisotropic exchange interactions Shehrin Sayed, Pratik Brahma, Cheng-Hsiang Hsu, Sayeef Salahuddin Recently, 5d and 4d oxides and halides with honeycomb lattice structures are of great interest for sizeable anisotropic exchange interaction leading to new magnetic ground states. We will discuss an interplay between the isotropic Heisenberg and anisotropic Kitaev type exchange interactions in these materials, leading to a transition from ordinary insulator to topological edge states. The intrinsic magnetic ordering induces a magnetic gap in the electronic structure of the edge states. We specifically focus on the zigzag antiferromagnetic order under strong anisotropic interaction, where consecutive atomic chains exhibit altering magnetic orientation. We argue that the two edges have the same chirality in a sample with an odd number of atomic chains leading to a quantized anomalous Hall conductance. However, the two edges have opposite chirality when the number of atomic chains is even, leading to a cancellation of phases, giving a zero Hall conductance and a substantial longitudinal resistance, typically known as the axion insulator state. |
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U71.00017: Shubnikov–de Haas oscillations as a probe for topological insulators Joo Vitor Ignácio Costa, Denis R Candido, Sigurdur I. Erlingsson, Carlos Egues In this work we study the bulk Shubnikov–de Haas oscillations (SdH) of 2D topological insulators. Our approach uses the complete 4x4 BHZ model [1] and a phenomenological trace formula [2] for the density of states accounting for Landau-level quantization. Within the topological regime, our results show unusual beatings of the SdH oscillations for a wide range of parameters. These unusual beatings are related to the coexistence of both electron- and hole-like carriers, present in the “Mexican hat” regime. This suggests ordinary SdH oscillations as a probe for bulk 2D systems with non-trivial band topology. |
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U71.00018: Theoretical study on large gap quantum spin Hall materials – Bismuthene Gang Li Quantum spin Hall (QSH) and quantum anomalous Hall (QAH) effects hold great promise for future applications in spintronics and quantum computations. So far, their emergence has been limited to ultralow temperatures. A large topological gap is critical to increasing the operating temperature. We demonstrate that a px-py model on the honeycomb lattice with local spin-orbital coupling (SOC) favors a large topological gap. A prototype material to realize such a scenario is the two-dimensional honeycomb layer formed by bismuth atoms, i.e. bismuthene. The theoretical paradigm of such a high-temperature QSH effect can nicely extend to other group-V elements, different substrates, and even correlated d-orbital systems. As examples, we further show bismuthene/SiO2 and iron-halogenide as large-gap QSH and QAH insulators described by px-py and dxy-dx2-y2 models, respectively. |
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U71.00019: FTIR Characterization of Bi2Se3/Sb2Te3 Ultrashort-Period Superlattices Candice Forrester, Teodora Dragic, Ido Levy, Christophe Testelin, Maria C Tamargo Topological insulators (TIs) are novel materials that have a band structure comprising an insulating bulk and highly conductive surface states. These surface states exhibit exotic properties of interest in fundamental physics and novel applications, such as spintronics and quantum computing. In this context, much interest has developed surrounding the ability to alter and enhance the bandgap of the TI while reducing the bulk doping, which may compromise the effects of the unique surface properties. Previous studies of Bi2Se3/Sb2Te3 ultrashort-period superlattices predicted the effects that period thickness may have on the TI bandgap, with the intent to maximize topological phenomena [Nano Lett. 20, 3420 (2020)]. In this study, superlattices were grown by molecular beam epitaxy and characterized using Fourier Transform Infrared Spectroscopy (FTIR) to measure absorption and observe changes in bandgap as a function period thickness. Coupling variable temperature FTIR measurements and doping determination from Hall transport, we estimated the bandgap of each sample. The analysis shows shifts in the bandgap energy as the period is reduced. We present those results and discuss the influence of period thickness, confinement and doping on the optical transitions. |
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U71.00020: Bleustein-Gulyaev waves in topological insulators with piezoeléctric properties Juan Granada, David Fernando Rojas-Vallecilla, Nelson Porras-Montenegro A topological insulator with piezoelectric properties is considered and an action is proposed in order to find the equations of motion and the constitutive relations of the generalized coordinates of electrodynamic and elastic origin, paying special attention to the changes induced by the topological properties and the piezoelectric coupling on the magnetoelectric and electroelastic effects. The results are used to demonstrate that the electromechanical factor of the Bleustein-Gulyaev waves on the surface of a topological piezoelectric crystal of class C6v in contact with vacuum undergoes a second order correction in the fine structure constant, associated with the topological properties. |
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U71.00021: 2D Materials in Strong Magnetic Fields: Hofstadter physics from first-principles Vasil Rokaj, Markus Penz, Michael Sentef, Michael Ruggenthaler, Angel Rubio We present a first-principles approach for treating 2D materials from weak to strong magnetic fields [1] and more precisely from the integer to the fractal quantum Hall regime. Our approach relies on the expansion on a correlated basis consisting of Landau levels and Bloch waves. In this manner we are able to compute energy bands of 2D materials as a function of the magnetic field strength and to capture the fractal spectrum of the Hofstadter butterfly [2] from first-principles. Further, the connection of the fractal spectrum to experimental transport measurements [3] will be presented, and how our theory allows for the explanation of these measurements and the intricate phenomena related to the Hofstadter butterfly. |
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U71.00022: Kinetic theory derivation of Hall viscosity: Role of symmetries and quantum effects Alexander Abanov, Gustavo Monteiro, Sriram Ganeshan In this talk we present the Hall Viscosity formula for a 2D charged plasma with general energy dispersion in magnetic field, obtained via kinetic theory. In the collisionless regime and temperature much bigger than the gap between Landau levels, quantum effects can be captured by replacing the Maxwell-Boltzmann distribution by the Fermi-Dirac distribution. The discreteness of the Landau levels can be incorporated via Lifshitz-Kosevich method. For zero temperature we recover the Hall viscosity expressions for the Integer Quantum Hall effect in both isotropic and anisotropic systems. |
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U71.00023: Typical medium theory for disorder driven topological state Ka-Ming Tam, Hanna Terletska, Tom Berlijn, Xiangru Kong, Juana Moreno The typical medium theory has been recently generalized for the study of multi-orbital systems. The typical medium dynamical cluster approximation (TMDCA) is capable of reproducing quantitatively the phase diagram of the three-dimensional Anderson model, and the effects of disorder in material-specific multi-orbital models. We apply the TMDCA to study the topological Anderson insulator -- a disorder driven topological state. We compare the results with those from the transfer matrix method and the recursive Green function method. |
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U71.00024: Probing Topological Surface States at Room Temperature in (Bi1-xSbx)2Te3 Films Christian Greenhill, Jenna C Walrath, Vladimir A Stoica, Alexander Chang, Yen-Hsiang Lin, Carl T Boone, Roy Clarke, Ctirad Uher, Cagliyan Kurdak, Rachel Goldman BiSbTe alloys are a part of an intriguing class of quantum materials known as topological insulators (TIs). We present our investigation of the local band structure of topologically insulating (Bi1-xSbx)2Te3 thin films using scanning tunneling microscopy/spectroscopy (STM/S) and magneto-transport (MT) measurements. Both STS and Hall transport measurements reveal a tunable electronic structure, with a n-type to p-type crossover for (Bi1-xSbx)2Te3 thin films at x ≈ 0.6. However, Hall measurements show n-type conduction while STS shows p-type conduction for films of varying thicknesses. This n/p anomaly is due to the distinct transport behaviors of the bulk and surface states. We directly probe both bulk and surface states in these films using STS. Both the Fermi level and the Dirac point are located inside the bulk band gap, indicating bulk-like insulating behavior with accessible surface states. We further discuss bulk and surface contributions to conduction. Prior to this work, direct detection of topological surface states in BiSbTe systems has been achieved only for T<10 K. This work demonstrates the first direct measurement of topological surface states using STS at room temperature for any material. |
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U71.00025: Riemannian geometry of optical responses Junyeong Ahn, Guang-Yu Guo, Naoto Nagaosa, Ashvin Vishwanath Geometry of quantum states has proved to be a useful concept for understanding responses of condensed matters to static electromagnetic fields. On the other hand, it has been challenging to relate quantum geometry with resonant optical responses. The main obstacle is that optical transitions are properties of a pair of states, while geometrical properties have been defined for a single state. Therefore, geometric interpretations of optical responses, when possible, have been limited to two-level systems, where the two states involved in transitions are not independent. In this talk, I will present a general theory of Riemannian geometry in resonant optical processes. An optical response related to the Riemannian curvature tensor is identified. |
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U71.00026: Chalcogenide Spin Injection from Iron- and Nickel-Based Edge Modulation Doping Gabriel Marcus, David Carroll Transition metal dichalcogenides (TMDs) possess physical properties that make them potentially useful as both thermoelectric and topological insulator materials. Rapid, high-yield synthesis of TMDs like bismuth telluride, antimony telluride and bismuth selenide is possible through solution-liquid-solid (SLS) colloidal chemistry techniques. Subsequent edge doping with noble metals (e.g. silver and copper) is known to enhance TMD thermoelectric parameters such as conductivity and the Seebeck coefficient. Iron and nickel may also play roles as useful dopants thanks to their magnetic properties and potential for spin current injection at the chalcogenide-dopant interface. In this work, bismuth telluride and antimony telluride were synthesized and then doped with different iron and nickel concentrations using SLS chemistry. Preliminary studies of magnetic and thermoelectric performance are ongoing, while STM imaging and analysis of these materials will soon be undertaken. Possible applications of spin-injected TMDs range from quantum computation to gravitational wave detection to biomedicine. |
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U71.00027: Computational analysis of DSM and WSM devices Hamed Vakilitaleghani, Samiran Ganguly, Avik Ghosh Weyl and Dirac semimetals (WSM, DSM) are class of materials that can be used for spintronics applications. The important property of WSM and DSM materials that makes them suitable for spintronic devices is the charge to spin conversion. Recently the non local spin transport in a DSM Cd3As2 has been reported1. We employ a combination of LLG and NEGF method to further understand WSM/DSM-FM based devices. Here we show local, non local spin transport and Lifshitz transition calculations from our numerical model. We explore the interaction between a ferromagnet (FM) and WSM/DSM as a means to design an in-memory computing element. We also look at some device structures based on WSM/DSM and FM heterostructures which can be used to create a DRAM. Lastly, we show how to create a spin circuit model based on the LLG/NEGF calculations. |
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U71.00028: Topological Sensing with Photonic Arrays of Resonant Circular Waveguides Kiernan Arledge, Binbin Weng, Bruno Uchoa We propose a topological framework for robust chemical detection based on a photonic array of circular dielectric waveguides with a subwavelength grating structure. We show that the device can be designed to create a chemically-sensitive photonic edge mode which is impervious to most sources of disorder. By performing realistic simulations of such a device in the mid-infrared regime that includes absorption loss introduced by the chemical species, we were able to demonstrate the viability of the proposed sensor for applications in trace gas detection capable of reaching the pars-per-billion range at the millimeter scale. These findings suggest that chemical sensors based on topological photonic designs could provide a new pathway for the development of novel on-chip integrated photonic sensing technologies. |
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U71.00029: Band structure of magnetic type-I Weyl semimetal candidates PrAl(Ge,Si) Kevin Pakuszewski, Jean Souza, Mário Piva, Fanny Rodolakis*, Jessica L McChesney, Pascoal G. Pagliuso, Cris Adriano Weyl semimetals are materials characterized by surface states, which are identified by Fermi arcs, induced by the non-trivial topology of the bulk band structure. In this work, we used soft x-ray angular photoemission spectroscopy (SX-ARPES) and complementary bulk measurements in order to map out the topology of the type-I Weyl semimetal candidates PrAl(Ge,Si) [1,2]. The SX-ARPES measurements were obtained at the 29-ID beamline at APS synchrotron. Looking to the paramagnetic band structure and to the evolution of the magnetoresistance [3], we discuss the role of the crystalline electrical field effects when we substitute Ge for Si. |
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U71.00030: Magnetic Anisotropy in Quaternary Intermetallic Compound ErNi2B2C wonchoon lee From the c-axis resistivity ρc(H,T) of quaternary intermetallic compound ErNi2B2C for various temperature region and magnetic fields with H∥c and ∥ab of crystallographic axis which has the superconducting transition temperature Tc (10.8K for H=0 G) and Néel temperature TN ( 5.58K for H=0 G), magnetic anisotropy has been studied. From these ρc(H,T)’s, the superconducting upper critical field HC2(T) curves were investigated for H ∥c and H ∥ ab of crystallographic axis and its anisotropy in Hc2(T) curves is compared and discussed with the previous reported results from ab-plane ρab(H,T) measurements considering the anisotropic field dependence of Néel temperature and magnetic pair breaking which maybe arisen from the Er+3 sublattice. |
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U71.00031: It may be Possible to Improve the Performance of Particle Accelerators by adsorbing Gases or other atoms into their surface Richard Kriske Although it is already known that the adsorption of Nitrogen and Oxygen improves the performance of Particle Accelerators and of Carbon degrades the performance, it may be that the gases and vapors of many other elements can do the same. It may be that Mercury or other metals that can be transformed into a gas or vapor likewise change the performance of Particle Accelerators, by increasing the voltage gradient per meter that the material, such as Niobium can withstand. This Author would like to list those materials and their expected effect. |
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U71.00032: Spin susceptibility and field-induced chiral stability in non-unitary chiral superconductivity Hirono Kaneyasu, Kouki Otsuka, Susumu Date, Yasumasa Hasegawa Assuming non-unitary chiral p-wave state of Eu in D4h for superconductivity in Sr2RuO4(SRO), we show spin susceptibility and gap function in bulk state, and field-induced chiral stability generating paramagnetic current in 3-Kelvin(3K) phase of Ru-SRO. The results indicate that the non-unitary chiral Eu is one of candidates for superconducting state of SRO, as well as chiral even-parity Eg. |
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U71.00033: Imaging Nematic Transitions in Iron-Pnictide Superconductors with a Quantum Gas Fan Yang, Stephen Taylor, Stephen D Edkins, Johanna Palmstrom, Ian R 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 local measurements of emergent resistivity anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and structural transitions. More broadly, these measurements demonstrate the SQCRAMscope's ability to reveal important insights into the physics of complex quantum materials. |
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U71.00034: Short-range nematic fluctuations in Sr1-xNaxFe2As2 Shan Wu, Yu Song, Yu He, Alex Frano, Ming Yi, Xiang Chen, Hiroshi Uchiyama, Ahmet Alatas, Ayman Said, Liran Wang, Thomas Wang, Christoph Meingast, Robert J Birgeneau
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U71.00035: Design and characterization of single crystalline Bi-2223 mesas towards the observation of coherent terahertz radiation emitted from trilayer intrinsic Josephson junctions Kanae Nagayama, Genki Kuwano, Shohei Suzuki, Takuya Yuhara, Shinji Kusunose, Takanari Kashiwagi, Hidetoshi Minami, Kazuo Kadowaki, Shintaro Adachi, Shunpei Yamaguchi, Takao Watanabe, Manabu Tsujimoto Coherent and continuous terahertz electromagnetic radiation emitted from stacks of intrinsic Josephson junctions (IJJs) has been observed solely from a bilayer Bi-2212 system [L. Ozyuzer et al., Science vol. 318, p. 1291 (2007)]. In this study, we focus on a trilayer Bi-2223 system, which consists of triple superconducting copper oxide layers per unite cell. Since an optimally doped Bi-2223 crystal exhibits the superconducting critical temperature above 100 K, we can expect to obtain appreciable emissions at remarkably high operation temperatures. Here, we fabricate Bi-2223 rectangular mesas in a conventional manner using photolithography and argon ion milling techniques. Unfortunately, we have not yet succeeded in observing intense emission from Bi-2223 mesas. Nevertheless, there are indications that the trilayer Bi-2223 system differs essentially from the bilayer Bi-2212 system in terms of the c-axis interlayer coupling. In the poster, we will discuss the multiple quasiparticle branches seen in the current-voltage characteristics of the Bi-2223 mesas. We will also propose an improvement in the microfabrication processes so that we can obtain the intense emission signals from the Bi-2223 mesas. |
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U71.00036: Superconductivity in Sn intercalated 2H-TaS2 Soumen Ash, Ashok Kumar Ganguli One of the most effective technique to tune the physical properties of layered transition metal dichalcogenides is the metal intercalation approach. Successful Sn intercalation into the van der Waals (vdW) layers of 2H-TaS2 was achieved by solid state reactions which led to formation of polycrystalline SnTaS2. SnTaS2 crystallizes into a centrosymmetric hexagonal structure (space group: P63/mmc) where Ta occupies the trigonal-prismatic position coordinated with S atoms and Sn accommodates the octahedral site, create alternative layers of TaS2 and Sn. The charge density wave (CDW) in 2H-TaS2 got totally suppressed due to the intercalation, leading to a superconducting phase with Tc~ 2.8 K. Superconductivity was further confirmed from the Meissner effect observed in the DC magnetic susceptibility. The characteristic upper and lower critical fields are found to be μ0Hc2(0) = 1458 Oe and μ0Hc1(0) = 45.5 Oe respectively. From the superconducting coherence length ξGL(0) = 47.5 nm and the penetration depth λGL(0) = 243 nm, the Ginzburg-Landau parameter is determined to be κ = 5.12 which indicates that SnTaS2 is a type-II superconductor with the thermodynamic critical field value μ0Hc(0) = 202 Oe. |
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U71.00037: Using Uniaxial Stress to Probe the Relationship between Competing Superconducting States in a Cuprate with Spin-stripe Order Zurab Guguchia, Debarchan Das, Chennan Wang, Tadashi Adachi, Nobuyoshi Kitajima, Mathias Elender, Felix Bruckner, Shreenanda Ghosh, Vadim Grinenko, Toni Shiroka, Markus Muller, Christopher M Mudry, Chris Baines, Marek Bartkowiak, Yoji Koike, Alex Amato, John Tranquada, Hans-Henning Klauss, Clifford W Hicks, Hubertus Luetkens Understanding to which degree charge, spin, and superconducting orders compete or coexist is paramount for elucidating the microscopic pairing mechanism in the cuprate high-temperature superconductors (HTSs). In this talk, I will report muon spin rotation and magnetic susceptibility experiments on in-plane stress effects on the static spin-stripe order and superconductivity in the cuprate system La2−xBaxCuO4 with x = 0.115. An extremely low uniaxial stress of 0.1 GPa induces a substantial decrease in the magnetic volume fraction and a dramatic rise in the onset of 3D superconductivity, from 10 to 32 K; however, the onset of at-least-2D superconductivity is much less sensitive to stress. These results show not only that large-volume-fraction spin-stripe order is anticorrelated with 3D superconducting coherence but also that these states are energetically very finely balanced. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. These results strongly suggest a similar pairing mechanism for spin-stripe order and the spatially modulated 2D and uniform 3D superconducting orders, imposing an important constraint on theoretical models. |
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U71.00038: Modeling random strain by means of a random-field Ising-O(3) model Nathaniel Page, Thomas Vojta Several iron-based superconducting materials feature a structural phase transition as well as a magnetic transition into a low-temperature phase with stripe-like spin-order. We study the relation between the structural and magnetic phase transitions in these materials by means of Monte Carlo simulations, and we analyze the effects of random strain commonly found in the samples. |
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U71.00039: Investigation by Undergraduates of the Superconducting Energy Gap of Ph-Doped and Co-Doped Iron Pnictides at 2-24 Kelvin Brett A Conti, Keeran Ramanathan, Dan Fauni, Erik Cauley, Chenlin Zhang, Yu Song, Guotai Tan, Pengcheng Dai, Roberto Ramos The discovery of iron-based superconductors, where multiple superconducting energy gaps have been observed, has led to research studies of multi-band superconductivity. In these novel superconductors, the observed energy gaps are anisotropic and largely depend on the way that the crystal has been grown and how contact is made to access tunneling directions. In this work, we report the results of tunneling spectroscopy experiments on iron-pnictide crystals that were contacted using silver paint. We report the results of four-wire differential conductance measurements using two lock-in amplifiers of the energy gap of phosphorus-doped BaFe2(As1-x Px)2 where x = 0.204, 0.304, 0.25, 0.39, 0.43 and 0.69 and x = 0.08 for the cobalt-doped Ba(Fe1-x Cox)2As2. The differential conductance dI/dV of these samples exhibit broad peaks and shoulders with Δ 1 = 2-5 meV, and Δ 2 = 7-10 meV. Some of these results were reproducible over similar samples, correspond well with existing data from literature while other features appear new. We report temperature-dependent features that we are in the process of anayzing. These measurements were performed fully by undergraduates. |
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U71.00040: Non-Local Vortex Transport in Superconducting W-C Nanowires Grown in a Helium Ion Microscope Pablo Orús, Rosa Córdoba, Gregor Hlawacek, JOSE MARIA DE TERESA NOGUERAS Focused Ion Beam Induced Deposition (FIBID) is an additive direct nanopatterning technique that has been used in the past to grow in-plane superconducting nanowires [1]. The lateral resolution of Ga+-FIB for patterning is nevertheless a limiting factor to achieve nanowire widths smaller than 50 nm. As it will be shown here, the good lateral resolution of the Helium Ion Microscope (HIM), in combination with the W(CO)6 precursor material, has allowed us to fabricate W-C superconducting nanowires with width down to 20 nm [2]. In devices based on these nanowires, large electrical voltages arising from non-local vortex transport have been measured. The obtained results will be compared to those observed previously in W-C nanowires grown by Ga+-FIBID [3]. |
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U71.00041: Designing nickelate superconductors with large crystal field splitting exploiting mixed-anion strategy Naoya Kitamine, Masayuki Ochi, Kazuhiko Kuroki Based on a combination of first principles and many-body calculations, we design mixed-anion nickelate superconductors with d8+δ electron configuration [1]. We adopt halogens or hydrogens as out-of-plane anions, which results in the band structure with large energy level offset between dx2-y2 and the other 3d orbitals. We find that if small amount of electrons are doped into the system, the four 3d band other than dx2-y2 being incipient and s±wave superconductivity is strongly enhanced. This result can be understood by the mathematical equivalence between the two-orbital model and the bilayer Hubbard model [2]. In fact, we can show, by orbital basis transformation, that the large level offset is approximately equivalent to large interlayer hopping in a bilayer system. The bilayer Hubbard model is known to exhibit high Tc s±wave superconductivity when the interlayer hopping is several times larger than the intralayer one and one of the bands located below Fermi level. |
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U71.00042: Influence of superconducting proximity effect in LSMO/SIO Ferromagnetic Resonance David Sanchez-Manzano, Santiago Carreira, Victor Rouco, Andrea Peralta, Fabian Cuellar, Alberto Rivera, Anke Sander, Carlos Leon, Javier E Villegas, Jacobo Santamaria Superconductivity and ferromagnetism are antagonistic phenomena: singlet-state Cooper pairs with antiparallel spins cannot survive in a ferromagnet. In some cases, triplet-state Cooper pairs, in which electrons have parallel spins, can be formed by proximity effect at ferromagnetic interfaces. We experimentally investigate ferromagnetic resonance (FMR) in trilayers consisting of a half-metallic La0.7Sr0.3MnO3 and YBa2Cu3O7 superconducting layers, with an interlayer of SrIrO3, a high spin-orbit coupling material, which is expected to create a strong inhomogeneity of the magnetic field in momentum space. The FMR signal is studied as a function of temperature (10-150 K). It reveals a drastic change in the resonance signal when the YBa2Cu3O7 becomes superconducting. This change will be discussed in terms of the formation of triplet Cooper, favored by the high spin-orbit coupling of SrIrO3. The results will be discussed in the frame of the spin-pumping theory considering the superconductor a spin sink where part of the FMR generated angular momentum can relax. |
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U71.00043: The Superconducting Gap in Weak to Strong Coupling Regime for High-Tc Superconductors. Radhika Chauhan, B. D. Indu The behavior of high-temperature superconducting gap in the various coupling regimes has been studied with the help of polaron Green's functions, developed via many-body quantum dynamics by a Hamiltonian that encompasses the contributions of electron, phonon, anharmonicities and impurities. The renormalized energies, energy line widths & shifts are described for polarons followed by the derivation of polaron density of states and superconducting gap equation. The developed gap equation is observed as the function of temperature, Fermi energy, and renormalized electron and phonon energy. The La2-xSrxCuO4 HTS has been hired for numerical analysis. The theory successfully explains the spectacular behavior of the superconducting gap in HTS. The temperature variation of the gap equation is found to be in good agreement with the BCS gap equation and reveals the value of transition temperature as 36.78 K, 37.50 K, and 38.52 K for electron-phonon coupling constant (gk) values 0.3, 0.7, and 1.1, respectively. This can be speculated from the obtained results that the Tc as well as superconducting gap (Δ) increases while approaching towards strong coupling regime from weak coupling regime. Also, the reduced gap ratio (2Δ(0) / kBTc ~ 6.5-7.0) is found in the limit (5-8) designated for HTS. |
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U71.00044: Superconducting properties of hyperbolic metamaterials based on ultrathin layers of NbTiN Will Korzi, Anne-Marie Valente-Feliciano, Joseph C Prestigiacomo, Michael Osofsky, Igor I 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 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 study of 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 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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U71.00045: Inducing superconductivity in ultra-clean van der Waals heterojunctions of monolayer MoS2 Prakiran Baidya, Divya Sahani, Hemanta Kumar Kundu, Awadhesh Narayan, Pratap Roy Chowdhury, Aveek Bid Inducing superconductivity in a semiconducting system with spin-orbit coupling has been an active area of research due to promising predictions and observation of exotic phases like Majorana mode. Our work has reported superconductivity in such a semiconducting system of a single-layer MoS2 induced by orbital coupling with a superconducting system of NbSe2. An important controlling parameter in inducing such proximity effect is the interface transparency, which in our work through low-temperature transport investigation of sharp Van-Der Waal heterojunctions of MoS2 and NbSe2 has been shown to be of 3 orders of magnitude higher than previously reported. Our first-principle-based study of electronic-structure calculations shows that this ultra-clean junction causes hybridization of orbitals of the two systems giving rise to states around Fermi level in MoS2, which facilitates the appearance of proximity effect in the system having a transition temperature and superconducting gap close to that of bulk NbSe2. Further study of the system's vortex dynamics shows a much higher pinning force compared to that of bulk, which has been primarily attributed to large defect-density in the parent MoS2. |
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U71.00046: Superconductivity in Th3P4-type noncentrosymmetric La3Se4 Moumita Naskar, Ashok Kumar Ganguli The thorium phosphide structure, Th3P4, occurs widely in the compounds of the lanthanides with selenium, sulfur and tellurium and have interesting electrical, superconducting or magnetic properties. Polycrystalline La3Se4 was synthesized via solid state reaction route. La3Se4 crystallizes in a noncentrosymmetric cubic Th3P4-type structure with space group: I-43d. Superconductivity with Tc~ 8.5 K has been confirmed from both the resistivity and magnetic susceptibility data. From the generalized Ginzburg-Landau model, the upper critical field Hc2(0) and coherence length ξGL(0) are found to be 8.09 T and 64 Å respectively. Superconductivity in noncentrosymmetric structures offer a wide ranging opportunites for the investigation of exotic properties. |
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U71.00047: Entropy fluxes versus magnetization currents in thermomagnetic phenomena Andrei Sergeev, Michael Reizer Having been generated by magnetic vector potential without the electromotive force, quantum currents (magnetization, superconducting, persistent and topological edge currents) do not produce entropy and cannot be created by thermal entropic forces. However, dozens of recent papers associate fluxes of the magnetization energy with the heat transfer. We demonstrate that the heat current, thermal forces, and thermomagnetic phenomena have entropic nature camouflaged by temperature dependent quantum currents. Entropic approach previously developed for collisionless thermomagnetic phenomena is generalized for interacting electrons with finite mobility. Both microscopic and phenomenological considerations show that giant thermomagnetic effects without particle-hole asymmetry are impossible in the Fermi liquid. |
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U71.00048: Vortex dynamics and nonlocal transport in superconducting films Aleix Bou Comas, Sarang Gopalakrishnan, Vadim Oganesyan In this study we assess the dynamics of pancake vortices and antivortices in a type-II superconductor at low temperature under conditions of inhomogeneous current biasing. We find and explore non-equilibrium steady states determined by vortex interactions. We also compare our results to experimental studies of non-local current-voltage response in NbSe2. |
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U71.00049: Charge density wave and superconductivity in Ta1-xMoxS2: evolution of structural and electronic properties. Jose Salcedo- Pimienta, Juan Mendoza Arenas, Jose Galvis Echeverry, Ian R Fisher, Luis Quiroga, Ferney Rodriguez, Paula Giraldo-Gallo
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U71.00050: Tuning supercurrent in Josephson field effect transistors using h-BN dielectric: Part 2, Characterization Fatemeh Barati, Josh P. Thompson, Matthieu Dartiailh, Kasra Sardashti, William a Mayer, Joseph Yuan, Kaushini S Wickramasinghe, Takashi Taniguchi, Kenji Watanabe, Hugh O. H. Churchill, Javad Shabani Josephson junction field effect transistors (JJ-FET) based on semiconductor weak-links can provide voltage-controlled supercurrent. Conventionally high-K dielectrics such as AlOx are used on FETs or JJ-FETS, here we introduce h-BN as an alternative gate dielectric for epitaxial Al/InAs JJ-FETs. This could solve several niche difficulties: 1. Reducing surface chemistry and defect formation. 2. Prevents microwave absorption. 3. Find use as a tunnel barrier. We investigate the Josephson properties of JJ-FETs fabricated with thin h-BN flakes (5 nm - 10 nm) and show high transparency of JJ-FET from epitaxial contacts are preserved. We also find that the product of normal resistance, Rn and critical current, Ic, is comparable for devices with hBN and AlOx dielectrics. However we observe differences in normal resistance of the junctions that suggest surface chemistry has not been affected by hBN compared to AlOx. |
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U71.00051: Anomalous inverse proximity effect in unconventional-superconductor junctions Shu Suzuki, Matthias Eschrig, Yukio Tanaka We investigate the effects of Andreev bound states due to the unconventional pairing on the inverse proximity effect of ferromagnet/superconductor junctions. Utilizing quasiclassical Eilenberger theory, we obtain the magnetization penetrating into the superconductor. We show that the direction of the induced magnetization is determined by two factors: whether Andreev bound states are present at the junction interface and the sign of the spin-mixing angle. In particular, when the Andreev bound states appear at the interface, the direction of the induced magnetization is opposite to that without Andreev bound states. Applying this novel effect, we can distinguish the pairing symmetry of a superconductor. |
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U71.00052: Superconductivity of binary hydrides Yundi Quan, Warren Pickett We have searched for and found several dynamically stable hydrides under pressure in the XH3, XH6 and XH10 structure classes. We analyze the systematic behavior of the electron-ion matrix elements, electron-phonon coupling constants and the phonon frequency moments etc. The gap functions, renormalization functions and the quasiparticle densities of states are also calculated and decomposed into contributions from the hydrogen atoms and the X atoms. We confirm and quantify that the hydrogen atoms play the dominant role in achieving high superconducting transition temperatures. Various aspects of the binary hydrides, such as anharmonic phonons, van Hove singularities near the Fermi level, and the effects of constant densities of states approximation will also be discussed. |
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U71.00053: Correlation between crystal purity and the charge density wave in 1T-VSe2 Charles Sayers, Liam Farrar, Simon J Bending, Mattia Cattelan, Alfred Jones, Neil Fox, Gabriele Kociok-Köhn, Konstantin Koshmak, Jude Laverock, Luca Pasquali, Enrico Da Como We discuss the charge density wave (CDW) properties of 1T-VSe2 crystals grown by chemical vapour transport (CVT) under varying conditions [1]. We find that by lowering the growth temperature (Tg < 630°C), there is a significant increase in both the CDW transition temperature and the residual resistance ratio (RRR) obtained from electrical transport measurements. Using x-ray photoelectron spectroscopy (XPS), we correlate the observed CDW properties with stoichiometry and the nature of defects. In addition, we have optimized a method to grow ultra-high purity 1T-VSe2 crystals with TCDW = (112.7 ± 0.8) K and maximum RRR value ∼ 49. Our work highlights the importance of carefully controlling the crystal growth conditions of strongly-correlated transition metal dichalcogenides. |
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U71.00054: Visualization of the Insulator-Insulator and the Insulator-mixed-Metal-Insulator-transitions in self-heated AlxV1-xO2 single crystals. Bertina Fisher, Larisa Patlagan, Anna Eyal, George M. Reisner In addition to the well-known insulator-metal-transition (IMT) from a monoclinic -M1 to rutile structure exhibited above room temperature by pure vanadium dioxide, the title materials with 0.005<x<0.02 exhibit an insulator-insulator-transition (IIT) from triclinic-T to monoclinic -M2 structure at temperatures RT<TIIT<TIMT. The decrease in resistance of single crystals at the TIMT is of several orders of magnitude; its increase at the TIIT is by a factor of < 2. While IIT is easily induced by heating or self–heating in single crystals of AlxV1-xO2, a mixed metal-insulator state sets in at TIMT because the low power in the metal cannot cover the losses. Reported herein is the investigation of the IIT and the Insulator-mixed-metal-insulator-transition (ImMIT) in self-heated single crystals of AlxV1-xO2 by optical microscopy synchronous with I-V tracing at RT. Prominent features on the current trace are easily identified with the onset of these self-heating induced transitions. In selected samples the video recordings showed that with increasing current, the embedded phase expands and with decreasing current it contracts, its boundaries receding in the first case or approaching until annihilation, in the second. |
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U71.00055: Density Wave Mediated Dzyaloshinskii-Moriya Interactions Ian Powell, Steven Durr, Sudip Chakravarty We investigate the effect that density wave states have on the localized spins of a square lattice. We find that topologically nontrivial density wave states can induce stable Dzyaloshinskii-Moriya (DM) interactions among the localized spins in the presence of an external magnetic field, and we study the resulting spin models for both antiferromagnetic and ferromagnetic backgrounds. While the density wave state itself can contribute to the the thermal Hall effect symmetry considerations preclude the resulting spin excitations from inducing a further thermal Hall effect. We utilize a Holstein-Primakoff (HP) substitution about the classical mean-field ground state to calculate the magnon dispersion for LSCO and find that the density wave induces a weak anisotropy; upon calculating the non-Abelian Berry curvature for this magnon branch we show explicitly that the magnon contribution to the thermal Hall conductivity is zero. Finally, we calculate corrections to the ground state energy, and the spin-wave dispersion due to the density wave for ferromagnetic backgrounds. We find that terms linear in the HP bosons can affect the critical behavior, a point previously overlooked in the literature. |
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U71.00056: Gauging away the Stoner model: Engineering unconventional metallic ferromagnetism with artificial gauge fields Joshuah Heath, Kevin Shawn Bedell For nearly a century, the Stoner model has dominated research in itinerant ferromagnetism, yet recent work on ultracold, optically trapped Fermi gases suggests that phase separation of spins occurs independent of long-range magnetic order. In this poster, we consider the breakdown of the Stoner criterion in a Landau-Fermi liquid with a weak non-zero gauge field. Due to a process analogous to Kohn’s theory of a metal-insulator transition, we find the stability of a Fermi liquid phase is strongly dependent on Landau parameters of mixed partial waves. Our work paves the way for the description of novel spintronic hardware in the language of Landau-Fermi liquid transport. |
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U71.00057: Two types of alternating spin-1/2 chains and their field-induced transitions in ε-LiVOPO4 Prashanta Mukharjee, Ranjith K M, Michael Baenitz, Yuri Skourski, Alexander Tsirlin, Ramesh Chandra Nath Thermodynamic properties, 31P nuclear magnetic resonance (NMR) measurements, and density-functional band-structure calculations for ε-LiVOPO4 are reported. This quantum magnet features a singlet ground state and comprises two types of alternating spin- 1/2 chains that manifest themselves by the double maxima in the susceptibility and magnetic specific heat, and by the two-step magnetization process with an intermediate 1/2 -plateau. From thermodynamic data and band-structure calculations, we estimate the leading couplings of J1 � 20 K and J2 � 60 K and the alternation ratios of α1 = J '1/J1 ≈ 0.6 and of α2 = J '<span style="font-size:10.8333px">2</span>/J<span style="font-size:10.8333px">2</span> ≈ 0.3 within the two chains, respectively. The zero-field spin gap △0/kB ≈ 7.3 K probed by thermodynamic and NMR measurements is caused by the J1-J'1 spin chains and can be closed in the applied field of μ0Hc1 ≈ 5.6 T, giving rise to a field induced long-range order. The NMR data reveal predominant three-dimensional spin-spin correlations at low temperatures. Field-induced magnetic ordering transition observed above Hc1 is attributed to the Bose-Einstein condensation of triplons in the sublattice formed by the J1-J'1 chains with weaker exchange couplings. |
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U71.00058: Magnetic structure of HoNiSi3 Rodolfo Tartaglia, Fabiana Rodrigues Arantes, Carlos William Galdino, Ulisses Ferreira Kaneko, Marcos a Avila, Eduardo Granado HoNiSi3 is an intermetallic compound which crystallizes in an orthorhombic structure (Cmmm space group). Specific heat measurements show two clearly distinct phase transitions, TN1 = 6.3 K and TN2 = 10.4 K, marked by well-defined λ-shape anomalies. In addition, magnetic susceptibility measurements revealed that the magnetic response at TN1 happens when the field is applied along the c axis, while at TN2 happens with the field applied along with a.1 In order to shed light onto the intriguing magnetic behavior of HoNiSi3, we have performed polarized resonant X-ray magnetic diffraction experiments. Our results show magnetic intensities at the same position of nuclear Bragg peaks below TN1 and TN2. This indicates a magnetic structure having a + - + - stacking pattern of ac ferromagnetic planes along b with propagation vector k = [0,0,0]. Also, we discriminate the signal from different projections of the total magnetic moment and infer that at temperatures between TN1 and TN2 the ordered magnetic moment points along the a-axis, while below TN1 an additional component along c arises, in agreement with magnetic susceptibility measurements. |
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U71.00059: Coupled dimer and bond-order-wave order in the quarter-filled one-dimensional Kondo lattice model Yixuan Huang, Donna Sheng, Chin-Sen Ting Motivated by the experiments on the organic compound (Per)_{2}[Pt(mnt)_{2}], we study the ground state of the one-dimensional Kondo lattice model at quarter filling with the density matrix renormalization group method. We show a coupled dimer and bond-order-wave (BOW) state in the weak coupling regime for the localized spins and itinerant electrons, respectively. The quantum phase transitions for the dimer and the BOW orders occur at the same critical coupling parameter J_{c}, with the opening of a charge gap. The emergence of the combination of dimer and BOW order agrees with the experimental findings of the simultaneous Peierls and spin-Peierls transitions at low temperatures, which provides a theoretical understanding of such phase transition. We also show that the localized spins in this insulating state have quasi-long ranged spin correlations with collinear configurations, which resemble the classical dimer order in the absence of a magnetic order. |
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U71.00060: Spin reorientation in CoV2O4 thin film from first principles calculation Mukesh Sharma, Tulika Maitra AV2O4 shows an interplay between spin, lattice and orbital degrees of freedom which manifests in the multiple structural and magnetic phase transitions. CoV2O4 (CVO) shows no or very weak cubic to tetragonal structural phase transition and two magnetic (paramagnetic to collinear ferrimagnetic (FM) and collinear to noncollinear FM) phase transitions at lower temperatures in its bulk form. In a recent experiment, an epitaxial thin film of CVO grown on the SrTiO3 (001) substrate, is observed to have an orthorhombic structural phase accompanied by a noncollinear magnetic state where the spin moments of Co and V are reoriented from (001) (seen in the bulk form) to the (110) direction. In this work, we have explored this complex noncollinear magnetic ground state by investigating the electronic, magnetic, and structural properties of CVO thin film using the first principles density functional theory. Our calculations show that the large exchange coupling strength in ab-plane as opposed to the c-direction in the orthorhombic phase can possibly explain the shifting of the FM easy axis to the (110) plane. Our calculated the ground state noncollinear magnetic structure shows a two-in-two-out form of V moments on each V4O4 cube, The possible orbital ordering has also been explored. |
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U71.00061: Nonlinear conduction detected by the harmonic measurement in an organic molecular conductor α-(BEDT-TTF)2I3 Mayu Ishii, Ryuji Okazaki, Masahumi Tamura We have investigated the nonlinear conduction of an organic molecular conductor α-(BEDT-TTF)2I3 in the charge order phase by measuring the harmonic component of the output voltage obtained when an alternating current is applied. Extrinsic components due to waveform distortion in the amplifier are usually included in the signal, which were carefully removed to attain high sensitivity to detect intrinsic nonlinearity. Thus, we have identified the intrinsic nonlinear conduction in low current region (~nA), in which non-ohmic response has not seen in the conventional I-V characteristic measuring method [1]. To explain our result, we suggest a model in terms of nonequilibrium hot charge carriers [2], in which the carrier mobility varied with electric field. [1] K. Kodama et al., J. Phys. Soc. Jpn 81, 114722 (2012). [2] T. Peterseim et al., PRB. 93, 245133 (2016). |
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U71.00062: Orientational order parameters for arbitrary quantum systems Michael te Vrugt, Raphael Wittkowski The concept of orientational order is of central importance for both classical liquid crystals and quantum-mechanical systems such as superconductors. In classical systems, order parameters can be obtained through systematic orientational expansions [1]. We generalize this method to quantum mechanics based on an expansion of Wigner functions. This provides a unified framework applicable to arbitrary quantum systems [2]. The formalism recovers the standard definitions for spin systems. For Fermi liquids, the formalism reveals the nonequivalence of various definitions of the order parameter used in the literature. Moreover, new order parameters for quantum molecular systems with low symmetry are derived, which cannot be properly described with the usual nematic tensors. |
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U71.00063: Superfluidity of dipolar excitons in a double layer of alpha-T3 with a mass term Yonatan Abranyos, Godfrey Anthony Gumbs, Oleg L. Berman We predict the Bose-Einstein condensation and superfluidity of dipolar excitons, formed by electron-hole pairs in spatially separated gapped hexagonal α-T3 (GHAT3) layers. The two possible model Hamiltonians of charge carriers in a GHAT3 monolayer include two possible expressions for an effective mass term, which can be generated either (1) by the effective magnetic field or (2) the site energy difference on different sublattices, which has been found in photonic crystals and optical lattices. This effective mass term opens a gap between the valence and conduction bands. We calculate the binding energy for a single dipolar exciton in a GHAT3 double layer for both Hamiltonians (1) and (2). For a weakly interacting Bose gas of dipolar excitons in a GHAT3 double layer, we obtain the energy dispersion of collective excitations, the sound velocity, the superfluid density, and the temperature of the Kosterlitz-Thouless (KT) phase transition. We compare the exciton binding energies and KT temperatures for both mechanisms of the gap opening to predict which mechanism will result in the formation of more stable excitons and the creation of the superfluid at higher temperatures at the same interlayer separations and exciton concentrations. |
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U71.00064: Studying the Metal-Insulator Transition of VO2 with GGA Daniel Koch, Kumar Prabhakaran, Mohamed Chaker, Sergei Manzhos Studying the metal-insulator transition (MIT) of VO2 from first-principles generally requires the use of computationally expensive hybrid density functionals, while the less resource-intense functionals of the generalized gradient approximation (GGA) -type commonly fail to correctly describe the relative thermodynamic stabilities, crystal-, or electronic structures of the semiconducting and metallic monoclinic and rutile phases of VO2. Unfortunately, investigating e.g. the effect of low-concentration doping on the VO2 transition temperature requires simulation cell dimensions for which hybrid density functionals quickly become unfeasible. We present an overview of the underlying difficulties connected to the use of GGA functionals on the VO2 MIT in commonly employed quantum chemistry codes and demonstrate that a computational setup using localized basis functions, pseudopotentials and a GGA functional with a small Hubbard correction helps achieving simultaneous description of qualitative band structure features, crystal geometries, and the MIT temperature of VO2 correctly. |
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U71.00065: Magnetic Field-Suppressed Geometrical Frustration in the Kagome Metal CoSn Jie Zhang, Hu Miao, Brian Craig Sales Layered Kagome networks host dispersionless low-energy excitations due to phase-destructive interference. Bringing these so-called flat bands in proximity to the Fermi level enables spin fluctuations. The magnetotransport signature of these systems is underexplored. In the frustrated paramagnetic CoSn Kagome metal, we observe a directional negative magnetoresistance in contrast to other transition metal flat band systems like FeSn, PtTl, and RhPb. We attribute this to the existence of a flat band in proximity to the Fermi level, which is consistent with our ARPES and resistivity anisotropy data. We also study the effect of magnetic/nonmagnetic doping. These transport findings prototype CoSn as an exciting platform to explore frustrated quantum states in the Kagome-derived flat band systems. In this talk, a systematic transport study as well as spectroscopy results will be presented. |
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U71.00066: Origin of the monoclinic distortion and its impact on the electronic properties in KO2 Olga Sikora, Dorota Gotfryd, Andrzej Ptok, Malgorzata Sternik, Krzysztof Wohlfeld, Przemyslaw Piekarz, Andrzej Oles Potassium superoxide KO2 is a p-electron system in which the interplay between spin, orbital and lattice degrees of freedom leads to a complex phase diagram. We use the density functional theory and lattice dynamics calculations to reveal the mechanism of formation of the low-temperature monoclinic phase [1]. We show dynamical instability of the high-temperature tetragonal structure and identify a soft phonon mode leading to the monoclinic C2/c symmetry and thus demonstrate a displacive character of the structural transition. The origin of enhanced insulating gap in the monoclinic phase is discussed within the model including the Hubbard U in the valence orbitals of the O2- ions. In the tetragonal phase without an orbital order, a small gap of 0.5 eV appears only if the spin-orbit interaction is taken into account. However, the lattice distortion present in the monoclinic structure induces orbital order via the Jahn-Teller effect, and the local Coulomb interactions increase the insulating gap to approximately 1.1 eV. |
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U71.00067: Impact of internal anisotropy on integer quantum Hall effect electronic phases Orion Ciftja We study the integer quantum Hall effect state at filling factor one of the lowest Landau level in presence of an anisotropic Coulomb interaction potential between electrons where anisotropy is incorporated via a phenomenological parameter. Such a potential represents a nontrivial source of internal anisotropy to the original integer quantum Hall phase under consideration. The objective of the work is to gain insight on the impact of such an anisotropic interaction potential on the energy stability of the liquid state. We adopt a widely used model of electrons immersed on disk geometry. It is found that this particular choice of the anisotropic Coulomb potential leads to a problem that is amenable to an analytical calculation of the energy per particle of the system in the thermodynamic limit. The results suggest that any presence of internal anisotropy in the interaction potential increases the overall energy of the system relative to the value corresponding to an isotropic liquid Coulomb potential. This, in turn, implies that another liquid phase with broken rotational symmetry may become energetically favorable when the interaction potential has a sufficient degree of anisotropy. |
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U71.00068: Nature of Mott transition in a hydrogen lattice Wei Ku, Zijian Lang, Sudeshna Sen, Vladimir Dobrosavljevic Mott transition, a electron correlation induced metal-insulator transition, has long been realized in many materials. Yet, the microscopic nature of the transition proposed by Mott has not been carefully examined in these materials, even by modern theories. This is because Mott's original proposal makes use of non-linear change of screening of long-range Coulomb interaction that are almost always ignored in simple models used in previous study of Mott transition. Here we study the Mott transition of an artificial hydrogen lattice including both the long-range Coulomb interaction and the strong on-site correlation, via an dynamical mean-field extension of density functional calculation. We found that in the relevant range of lattice spacing, the system is in the charge-transfer regime, namely the charge fluctuation involves mostly higher energy orbitals beyond 1s one, rendering a single-band Hubbard model inadequate. Interestingly, Mott transition occurs when atomic bound states are still present. Our study challenges Mott's original microscopic picture and reveal some key physics of metal-insulator transition in realistic materials. |
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U71.00069: Electrically excited size and shape oscillations of bubbles in liquid helium-4 Pranaya Rath, Vaisakh Vadakkumbatt, Emil Mathew Joseph, Udit Choudhry, Yunhu Huang, Ambarish Ghosh Electrons on the surface of liquid helium form a defect-free 2D electron system (2DES). Multielectron bubbles (MEBs) are cavities in liquid helium with a large number of electrons pushed against the inner surface of the bubbles, and they provide a platform to study this system of interacting electrons on curved surfaces and at high charge densities. The coupling of electrons with the surface of an MEB can be probed by observing the size and shape fluctuations of the MEBs, which in turn can be excited using electrical fields. In our experiments, the MEBs were attached to a dielectric surface. Electrical excitation of various frequencies was used to excite and identify the various normal modes of the bubbles. The experimental resonant frequencies were found to be slightly higher than the theoretical predictions for a bubble in bulk, and this difference is further investigated computationally. We believe understanding the resonance and dissipation of the surface modes can lead to a better understanding of the behavior of 2DES in MEBs. |
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U71.00070: Deconfined quantum criticality and emergent SO(5) symmetry in fermionic systems Hong Yao, Zixiang Li, Shaokai Jian Deconfined quantum criticality with emergent SO(5) symmetry in correlated systems remains elusive. Here, by performing numerically-exact state-of-the-art quantum Monte Carlo (QMC) simulations, we show convincing evidences of deconfined quantum critical points (DQCP) between antiferromagnetic and valence-bond-solid phases in the extended Hubbard model of fermions on the honeycomb lattice with large system sizes. We further demonstrate evidences of the SO(5) symmetry at the DQCP. Moreover, it is the first time that the critical exponents obtained at the DQCP are consistent with the rigourous conformal bounds. Consequently, we establish a promising arena of DQCP with emergent SO(5) symmetry in interacting systems of fermions. Its possible experimental relevances in correlated systems such as graphene-family materials will be discussed briefly [1]. |
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U71.00071: Optical properties of the quasi-one-dimensional magnet CeIr3B2 Ken ONeal, Jian-Xin Zhu, Eric D Bauer, Filip Ronning, Dmitry Yarotski, Rohit P Prasankumar We present the optical properties of the quasi-one-dimensional (1D) magnet CeIr3B2 over a broad temperature range covering the ferromagnetic Curie temperature, Tc=41 K. Polarized spectroscopic measurements combined with first principles density functional theory calculations reveal that the optical response is dominated by the light polarization with respect to the direction of the quasi-1D chains. Suppression of the low frequency optical conductivity with decreasing temperature will be explained within the Kondo lattice framework. Moreover, we will also discuss signatures of spin-charge coupling across Tc. |
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U71.00072: Thermopower of the two-dimensional disordered electron gas Zahidul Islam Jitu, Alexander Finkelstein, Karen Michaeli, Georg Schwiete We study interaction corrections to the thermopower of the disordered electron gas at low temperatures. To this end, we calculate the density-heat density correlation function in the non-linear sigma model formalism. It is known that the thermal conductivity acquires two types of logarithmic corrections, conventional Altshuler-Aronov corrections as well as additional corrections originating from a sub-temperature interval of energies, which arise only in the presence of long-range Coulomb interactions. Here, we study the influence of both types of corrections on the temperature dependence of the thermopower. |
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U71.00073: Heterogenous nucleation at twin boundaries in a VO2 thin film revealed by nano-optical spectroscopy Aaron Sternbach, Frank Ruta, Yin Shi, Tetiana Slusar, Samuel Moore, Alexander McLeod, Jacob Schalch, Guangwu Duan, Xin Zhang, Mengkun Liu, Hyun-Tak Kim, Richard Averitt, Long-Qing Chen, Dmitri Basov Symmetry lowering phase transitions allow each unit cell of a derived phase to assume one of several variants of the crystallographic orientation. As a result self-organized twin-domains can form on mesoscopic length-scales. Polarized microscopy is an established approach to characterize the local crystallographic orientation of such domains. However, the inherent limitations of diffraction forbid the observation of nanotextured domain patterns with conventional microscopy. Here, I discuss an accurate approach to model the frequency dependent nano-optical contrast in low symmetry crystalline structures. Comparison between the model calculations and our experimental data show good agreement for two expected twin-domain orientations in a VO2 thin film. In our model, the nano-optical contrast between domains stems from the anisotropic character of phonon-polaritons. Thus our approach may enable fingerprint assignment of the local crystallographic orientation in nanotextured domains. Co-located nano-optical images at distinct infrared frequencies directly reveal real-space correlations between the twin-domain nanotexturing and locations where metallic domains emerge at the onset of the transition region. |
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U71.00074: RKKY interaction in a doped pseudospin-1 fermion system at finite temperature Dmytro Oriekhov, Valery Gusynin We study the RKKY interaction of magnetic impurities in the α-Τ3 model which hosts pseudospin-1 fermions with |
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U71.00075: Electronic and vibrational spectroscopy of miscible MgO-ZnO ternary alloys Kemal Aziz, Chinedu Ekuma The ordered structure of MgO-ZnO alloy system is a versatile tunable optical material promising for diverse optoelectronic applications. However, isovalent and isostructural alloy compositions of MgO-ZnO are generally unstable at ambient conditions. Using state-of-the-art ab initio evolutionary simulations, we predict and study the properties of stable phases of MgO-ZnO. We establish the dynamical stability of the predicted crystal structures through the phonon and Raman spectroscopy. Detailed analyses of two of the most stable structures reveal highly tunable properties that could be explored for photonic and optical applications. |
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U71.00076: Ion Permeation Through Thermally Tuned Microstructure in Graphene Oxide Membranes Vasumathy Ravishankar, Sundara Ramaprabhu, Manu Jaiswal Graphene oxide (GO), an important material for sieving and filtration, has hierarchical microstructure; nanosheets of uniformly stacked GO with separations termed “nanochannels” form “lamellae”. In thick GO films, collections of lamellae are separated by voids. Current literature proposes ion permeation assuming GO as consisting only of lamellae. However, the contribution of voids cannot be ignored. In this work, electro-impedance spectroscopy was used to study GO films annealed between temperatures of 100 °C and 200 °C, aiming to discern contributions of nanochannels and voids. Responses were fit using equivalent circuits. Annealing increases microstructural disorder and thus increases number of voids and also decreases nanochannel width, as ascertained from X-ray diffraction. EIS detected two processes; decreasing charge transfer resistance Rct (from 91 kΩm-2 for as-prepared GO to 113 Ωm-2 for GO annealed at 160 °C) and exponentially increasing permeation resistance RP (from 112 Ωm-2 for as-prepared GO to 1.5 kΩm-2 for GO annealed at 160 °C). Increase in RP despite increase in microstructural disorder suggests that nanochannels play a dominant role in ion permeation. Presence of strong dynamic for GO films annealed at 180 °C and 200 °C confirms this conclusion. |
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U71.00077: Dipolariton propagation in a van der Waals TMDC with Ψ-shaped channel guides and buffered channel branches. Patrick Serafin, German Kolmakov Using a computational approach based on the driven diffusion equation for a dipolariton wave packet, we simulate the diffusive dynamics of dipolaritons in an optical microcavity embedded with a transition metal dichalcogenide (TMDC) heterogeneous bilayer encompassing a Ψ-shaped channel. By considering exciton dipolaritons, which are a three way superposition of direct excitons, indirect excitons and cavity photons; we are able to drive the dipolaritons in our system by the use of an electric voltage and investigate their diffusive properties. More precisely, we study the propagation of dipolaritons present in a MoSe2-WS2 heterostructure, where the dipolariton propagation is guided by a Ψ-shaped channel. We also consider the propagation of dipolaritons in the presence of a buffer in the Ψ-shaped channel and study the resulting changes in efficiency. By our consideration of a geometrically novel dipolariton channel guide, we are able to replicate the dipolariton redistribution efficiencies of previously proposed polaritronic applications and introduce novel designs for optical routers at room temperature. |
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U71.00078: Computational Synthesis of 2D Materials: A High-Throughput Approach to Materials Design Tara Boland, Arunima Singh The emergence of two-dimensional materials opened up many potential avenues for novel device applications such as nanoelectronics, topological insulators, field-effect transistors, microwave and terahertz photonics, and many more. Of the more than 1,000 theoretically predicted 2D materials, only 55 2D materials have been experimentally synthesized. Our database contains energetic and structural properties for 2D heterostructures, computed using van der Waals corrected density functional theory, highlighting suitable substrates from which to synthesize 2D materials. For heterostructures that meet certain stability criteria, the density of states is computed to characterize the electronic properties of these materials for device applications. |
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U71.00079: On-surface synthesis of heteroatom-doped graphene nanoribbons Gang Li, Amir Taqieddin, Jacob Teeter, Percy Zahl, N. R. Aluru, Alexander Sinitskii The bottom-up approaches have been demonstrated to be very efficient for preparing atomically precise GNRs with tailor-made physical properties. The bottom-up on-surface synthesis enables incorporation of various heteroatoms, such as boron, nitrogen, sulfur and oxygen, into the GNR structure. Heteroatom doping can be a powerful tool for tuning the electronic properties of GNRs. The on-surface growth and characterization of heteroatom-doped GNRs is still largely unexplored and the development of new methods for their synthesis remains highly desirable. Here we describe facile on-surface methods for preparing several new heteroatom-doped GNRs that were modified with nitrogen, sulfur or boron atoms. The structures of these GNRs were identified by scanning tunneling microscopy (STM) in combination with noncontact atomic force microscopy (nc-AFM). The electronic structure of GNRs was investigated by scanning tunneling spectroscopy (STS) measurements in combination with DFT and GW calculations, showing good agreement between the experimental and theoretical results. These new heteroatom doped GNRs may find applications in a variety of electronic and optoelectronic devices. |
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U71.00080: Thickness-Dependent Ambient Effects on the Curie Temperatures and Magnetic Domains of Metallic Two-Dimensional Magnets Ti Xie, Yeonghun Lee, Jinling Zhou, Alemayehu S. Admasu, Nagarajan Valanoor, John Cumings, Sang-Wook Cheong, Ichiro Takeuchi, Kyeongjae Cho, Cheng Gong The emergent magnetic two-dimensional (2D) materials provide ideal solid-state platforms for a broad range of applications including miniaturized spintronics and magnetoelectric sensors. Owing to the general air sensitivity of 2D magnets, the understanding of ambient effects on 2D magnetism is critical. Apparently, the nature of itinerant ferromagnetism potentially makes metallic 2D magnets insensitive to environmental disturbance. Nevertheless, our systematic study showed that the Curie temperature of metallic 2D Fe3GeTe2 decreases dramatically in the air but thick Fe3GeTe2 exhibits self-protection. Remarkably, we found the air exposure effectively promotes the formation of multiple magnetic domains in 2D Fe3GeTe2, but not in bulk Fe3GeTe2. Our first-principles calculations support the scenario that substrate-induced roughness and tellurium vacancies boost the interaction of 2D Fe3GeTe2 with the air. Our elucidation of the thickness-dependent ambient effects on the Curie temperatures and magnetic domains in 2D magnets provides critical insights for chemically decorating and manipulating 2D magnets. |
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U71.00081: Fully integrated graphene-based optomechanical systems Aneesh Dash, Shankar Kumar Selvaraja, Akshay K Naik Graphene has been promising for modern nanophotonic and nanomechanical research, with many applications beyond the limits of conventional materials. Tunable electro-refraction, electro-absorption, all-optical modulation, and frequency-comb generation make it a powerful nanophotonic material. Similarly, strain-tunable graphene nanoresonators have opened new frontiers in studying nonlinear dynamics, quantum mechanics, and ultra-sensitive nanomechanical sensing. Optomechanical systems based on graphene, that harness both its optical and mechanical properties, have been a topic of research interest for novel quantum measurements and sensing applications. However, most of these systems are based on free-space optics or semi-integrated optics. While there have been recent efforts to fully integrate these systems on a single chip, numerous issues impede these efforts. We theoretically propose optical actuation (with forces in nN) and detection schemes (with sensitivity in fm/Hz½) for graphene nanomechanical resonators integrated on silicon-photonic platforms, identify the limitations of these systems, and propose potential applications of these systems as on-chip optomechanical probes for hybrid optical modes. |
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U71.00082: van der Waals photothermoelectric effect in atomic layer heterojunctions Yunqiu (Kelly) Luo, Tong Zhou, Mahesh R Neupane, Alex Matos Abiague, Ryan Bailey-Crandell, Michael J Newburger, Igor Lyalin, Igor Zutic, Roland Kawakami Two-dimensional (2D) van der Waals (vdW) heterostructures provide exceptional opportunities for new physics and devices due to their unprecedented ability to tune the electronic, optical, magnetic, and spintronic properties by atomic layer stacking and electrostatic gating. Harnessing this versatility requires a fundamental understanding of light-matter interactions and establishing new functionalities for photon-charge and photon-spin conversions. Here, we report the first observation of a highly-tunable vdW photothermoelectric effect in dual-gated MoS2/graphene junctions with a striking multiple-polarity switching of photocurrent as a function of junction bias and carrier density. In stark contrast to photovoltaic effects arising from excitonic absorption in MoS2, the vdW photothermoelectric effect originates from photoexcitation of hot electrons in graphene and thermoelectric transport across the vdW junction. Systematic studies of photoconductance reveal vdW photothermoelectric effect as the dominant mechanism for photocurrent generation at room temperature, as opposed to excitonic absorption. These findings, further corroborated by our drift-diffusion bipolar transport model, provide an important step for understanding and control of vdW-interface devices. |
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U71.00083: Non-adiabatic Hall effect with non-Abelian Berry curvature in bilayer graphene Ci Li, Wei-Yuan Tu, Wang Yao For Bloch electrons moving in an external electric field, the coupling to remote bands with energy separation large compared to the field is well captured by the adiabatic approximation, which can manifest as the Berry curvature that gives rise to the Hall effect. On the other hand, when there are nearly degenerate bands, the non-perturbative inter-band transition between them can also induce a non-adiabatic Hall effect as recently discussed in monolayer graphene with a small gap. Here we consider an AB-stacked bilayer graphene system where both scenarios are relevant. The interband transitions between the lowest conduction band and top valence band are non-perturbatively treated, whereas their coupling to the higher energy bands result in non-Abelian Berry curvature in this two-band manifold. We find contributions to the current from both the non-Abelian Berry curvature and the interband coherence within the two-band manifold. |
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U71.00084: Optoelectronics based on Transition Metal Dichalcogenide/2D Perovskite Heterostructures Abin Varghese, Yuefeng Yin, Saurabh Lodha, Nikhil V. Medhekar The use of 2D perovskites in visible-range optoelectronics has been limited due to their wide bandgaps, low optical absorption, and large exciton binding energies. [1,2] Here, through density functional theory calculations, we show that conjugating transition metal dichalcogenides (TMD) with 2D perovskites (here, BA2PbBr4, BA=C4H9NH3+) to form heterostructures could enable different applications based on the bandstructure at the hetero-interface. |
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U71.00085: Rapid Mesoporous Carbon Complex Fabrication via Photothermal Process HSIN-JUNG YU, Huafeng Fei, James J Watkins, Kenneth Carter Mesoporous carbon containing well dispersed crystalline nanoparticles are interesting high performance materials. Here, we demonstrate a novel microsecond light pulse carbonization process that produces large area mesoporous carbon films containing well-dispersed titania nanoparticles. The process involves a bottlebrush copolymer which self-assembles into a spherical morphology. When combined with a phenol-formaldehyde resin which provided the carbon scaffold, and TiO2 nanoparticles which serve as a photocatalyst. A structure-property relationship was investigated for fast precursor formation of mesoporous carbon hybrid material. TiO2 loading as high as 50 wt% was achieved. This mesoporous hybrid material resulted in a 1.5-fold improved degradation potential over the reference bulk titania. The photocatalytic neutralization potential was tested on both an organophosphorus nerve agent and a environmental hazardous simulant. Apart from photocatalytic activity of the dispersed TiO2 nanoparticles, the mesoporous structure also led to highly absorbent properties. More notably, this rapid photothermal process used to fabricate porous material can be potentially applied to the design many other multifunctional mesoporous carbon-metal oxide hybrid materials. |
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U71.00086: Nanoscale-resolved spectroscopy of excitons in atomically-thin transition metal dichalcogenides Shuai Zhang, Baichang Li, Francesco Ruta, Yinming Shao, Aaron Sternbach, Alexander S McLeod, Zhiyuan Sun, Lin Xiong, Samuel Moore, Xinyi Xu, Wenjing Wu, Lin Zhou, Zhiying Wang, Essance Ray, Nathan P Wilson, P James Schuck, Michal Lipson, Xiaodong Xu, Xiaoyang Zhu, Michael Fogler, James Hone, Dmitri Basov Excitons play a dominant role in opto-electronic properties of atomically thin van der Waals semiconductors, such as transition metal dichalcogenides (TMDs). Further, excitons can be engineered by dielectric screening, interlayer hybridization and moiré potentials. These engineering knobs inherently lead to heterogeneous properties at the nanoscale. However, probing the optical response from excitons at the nanoscale is a formidable task. In this talk, we couple a tunable continuous-wave laser to a scattering-type scanning near-field optical microscope (s-SNOM), and measure the near-infrared optical spectra of a MoSe2 monolayer, WSe2 monolayer, MoSe2/WSe2 heterobilayer and WSe2 trilayer at nanoscale. The observed spectra, in all cases, reveal resonances that we attribute to excitonic optical responses and are resolved with 20 nm spatial resolution. Nanoscale-resolved dielectric functions can be extracted quantitatively from s-SNOM spectra. Further, the evolution of both exciton resonance energies and radiation rates in a MoSe2/WSe2 heterobilayer and a WSe2 trilayer relative to their isolated monoayers is investigated. Our work brings opportunities for locally exploring excitons with nanoscale spatial inhomogeneity, such as moiré exciton and exciton polarition. |
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U71.00087: Exploring the role of grain boundaries on the melting behavior of multi-grain gold nanoparticles Chance Barrett, Abdelkader Kara, Laurene Tetard Grain boundaries play a significant role in the mechanical and thermal properties of solid polycrystalline nanoparticles. However, both experimental and theoretical investigations of their structure and properties in a multi-grain system are challenging. Modeling of nanoparticles often considers single crystals with varying sizes, which is not representative of nanoparticles formed by chemical or physical processes. |
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U71.00088: Computational Synthesis of Atomically thin MoS2 Layer by MoO3 Reactants and H2S-H2 Precursors: A Quantum Molecular Dynamics Study Sungwook Hong, Aravind Krishnamoorthy, Subodh C Tiwari, Rajiv K Kalia, Aiichiro Nakano, Priya Vashishta Layered MoS2 is a promising transition metal dichalcogenides (TMDC) material due to its outstanding physical and chemical properties. Chemical vapor deposition (CVD) is the most effective method to bring this layered TMDC material into mass production. During CVD process, sulfurization of MoO3 reactants is an essential reaction step to grow atomically thin large MoS2 area. Recent studies suggested that addition of H2 gas in this synthesis process could lead to growth of higher-quality MoS2 monolayers. However, effects of H2 partial pressure on synthesis of MoS2 still remain elusive. Here, our quantum molecular dynamics (QMD) simulations reveal that the H2S/H2 mixture indeed reduce and sulfurize the MoO3 flake effectively, when compared with pure H2S precursors. We also identify key reaction pathways for the reactions of MoO3 reactants and H2S/H2 mixture, which may help experimental synthesis of higher quality MoS2 layers. We believe our work will make a unique contribution to the scalable growth of 2D TMDC materials for large-scale integration. |
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U71.00089: Chiral SO(4) spin-charge density wave and degenerate topological superconductivity in the MA-TBG Fan Yang, Chen Lu, Yongyou Zhang, Yu Zhang, Ming Zhang Starting from a realistic extended Hubbard model on the Honeycomb lattice, we perform a thorough investigation on the possible electron instabilities in the magic-angle-twisted bilayer-graphene near the van Hove (VH) dopings. Here we focus on the interplay between the approximate SU(2)×SU(2) symmetry and the D_3 symmetry of the system, which leads to intriguing quantum states relevant to recent experiments, as revealed by our systematic random-phase-approximation plus mean-field study. At the SU(2)×SU(2) symmetric point, the degenerate inter-valley SDW and CDW are mixed into a new state of matter dubbed as the chiral SO(4) spin-charge DW. This state simultaneously hosts three mutually perpendicular 4-component vectorial spin-charge DW orders, and possesses intriguing topological properties and Goldstone-mode fluctuations. Adding a weak symmetry-breaking perturbation can change this state to a nematic DW state with coexisting stripy CDW and SDW order parameters, consistent with recent STM observations. On the aspect of SC, we obtain degenerate triplet p + ip and singlet d + id topological superconductivity near the VH dopings. In addition, the two asymmetric doping-dependent behaviors of the obtained pairing phase diagram are well consistent with experiments. |
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U71.00090: Decorating MoS2 2-D materials with metal nanostructures for sensor applications Parveen Kumar, Pooja Chopra The monolayers of 2D-MoS2 have demonstrated distinctive electronic, optical, and catalytic properties. These 2D materials, with and without plasmon enhancement are studied and explored extensively for nanodevice applications ranging from bio/chemical sensors to medical monitors and photovoltaics. Plasmonic resonances strongly depend on the size, shape, spacing, and interaction of metal nanoparticles with semiconductor nanostructure. A lot of resources as well as efforts are required to realize plasmonic resonator devices and optimization with different shapes and sizes. In contrast, device modeling and simulations offer a much economical substitute to tackle such challenges. I am presenting models and simulations of nanoparticle plasmonic resonators decorated on 2-D MoS2 monolayers for sensing applications. |
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U71.00091: Finite-temperature plasmons and damping for α-T3 materials Andrii Iurov, Liubov Zhemchuzhna, Paula Fekete, Godfrey Anthony Gumbs, Danhong Huang We have numerically calculated the dynamical polarization function, the plasmon dispersion relation and their lifetimes due to Landau damping for various types of the recently discovered α-T3 lattices at finite temperature. We do so by choosing the hopping parameter 0 < α < 1. Both intrinsic and extrinsic cases with zero or finite Fermi energy and T = 0 have been addressed. We obtained analytic results for the plasmon dispersion relation in the long wavelength limit q → 0 for a dice lattice with α = 1. |
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U71.00092: Study of Electronic Structure and Topological Phenomena in Ti2N MXene Yogendra Limbu, Gopi Kaphle, Durga Paudyal The evolution of structural and electronic properties of graphene-like titanium nitride based MXenes have been studied with different functional groups (F, O, H, and OH) employ-ing first principles electronic structure calculations. The calculated formation and cohesive energies reveal the chemical stability of all MXenes and MAX phase. The MAX phase and all the studied defect free functionalized MXenes are metallic in nature except for oxygen termination, which expected to be semi-metallic . The bare MXene is nearly half metallic ferromagnet but after surface termination, it’s ferromagnetism gets destroyed. The strain effect significantly influences the Fermi level with the formation of Dirac topology. The variable topological phenomena have been studied in pristine and defected MXenes. Interestingly, the defect on MXene sheet Ti2NO2 significantly changed the electronic properties. Further, the Cr and Co substitutions in Ti2NO2 allow to convert the system to be ferromagnetic and para-magnetic with half metallicity respectively. However, Mn substitution preserves metalicity with ferromagnetic properties. |
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U71.00093: Research on energy, electronic structure, and magnetic changes for compression, sliding, and twisting for 2D Electrides (Y2C, Ca2N) based on the first principle GwanWoo Kim, Gunn Kim Using the first-principles calculations based on density functional theory (DFT), we have studied how the electron structure and total energy change when one of the layers is translated, rotated horizontally (21.8 °), and compressed vertically in the Ca2N and Y2C bilayer, which are representative two-dimensional electride materials. Elctrides show unique phenomena called interstitial anionic electrons (IAEs). |
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U71.00094: Quantum entanglement between two excitons in graphene under strain Gabriel Pimenta Martins, Oleg L. Berman, Godfrey Anthony Gumbs, Yurii E. Lozovik It has been shown that the Hamiltonian for excitons in graphene under strain is similar to that for the charge carriers in a magnetic field, which is not coupled to the charges. In this environment electrons and holes can form bound states in discrete Landau levels called Pseudomagnetoexcitons (PMEs). Provided that localization of charge carriers at the impurities on the graphene sheet removes degeneracy of Landau levels, PMEs can be treated as qubits. We assume the interaction between two such PMEs that are coupled to a single cavity mode. We have investigated the quantum entanglement of the pair of excitons by analyzing the concurrence in the system for several cases. We also considered an imperfect cavity, with leaking photons and numerically calculated how the concurrence evolves in time. For the system without dissipation, we applied a Jaynes-Cummings-like model for the interaction between two qubits in a single cavity mode. This was solved exactly for the resonant case, where the photonic energy is equal to the qubit energy gap. In the presence of dissipation, we numerically solved the Lindblad Master equation that governs the evolution. |
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U71.00095: Effect of Spin orbit coupling and magnetic field on the RKKY Interaction in a 2D EG Travis Rogowski, Godfrey Anthony Gumbs The interaction energy for the indirect-exchange or Ruderman-Kittel-Kasuva-Yosida (RKKY) interaction between magnetic spins localized on lattice sites of a 2D electron gas (EG) like in a MOSFET with spin-orbital coupling will be presented using linear response theory involving propagator Green’s functions. The effect due to magnetic field will be investigated taking into account both Landau quantization and the Zeeman term. Both analytical and numerical results will be discussed. |
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U71.00096: Correlated Insulating States at Fractional Fillings of the WS2/WSe2 Moiré Lattice Xiong Huang, Tianmeng Wang, Shengnan Miao, Chong Wang, Zhipeng Li, Zhen Lian, Takashi Taniguchi, Kenji Watanabe, Satoshi Okamoto, Di Xiao, Sufei Shi, Yongtao Cui Moiré superlattices of van der Waals materials, such as twisted graphene and transitional metal dichalcogenides, have recently emerged as a fascinating platform to study strongly correlated states in two dimensions, thanks to the strong electron interaction in the moiré minibands. In most systems, the correlated states appear when the moiré lattice is filled by integer number of electrons per moiré unit cell. Recent research in the WS2/WSe2 heterobilayer reported the correlated states at fractional fillings of 1/3 and 2/3 holes per moiré unit cell, hinting a long-range electron interaction in this system. In this work, employing a scanning microwave impedance microscopy technique that is sensitive to local electrical properties, we observe a series of correlated insulating states at fractional fillings of the moiré minibands on both electron- and hole-doped sides in angle-aligned WS2/WSe2 hetero-bilayers, with certain states persisting at temperatures up to 120 K. Our Monte Carlo simulations reveal that these insulating states correspond to ordering of electrons in the moiré lattice with a periodicity much larger than the moiré unit cell, indicating a surprisingly strong and long-range interaction beyond the nearest neighbors. |
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U71.00097: Theoretical investigation of bottom-up synthesized graphene nanoribbon transistors Yuxuan Lin, Gabriela Borin Barin, Zafer Mutlu, Juan P Llinas, Akimitsu Narita, Klaus Müllen, Pascal Ruffieux, Roman Fasel, Jeffrey Bokor Bottom-up synthesized graphene nanoribbons (GNRs) have shown great promise in next generation electronic devices because of the perfect precision and wide diversity of their atomic structures and their intriguing transport properties. The armchair, semiconducting bottom-up GNRs are of particular interest in future ultimately scaled transistor technologies. Here we present a device model for bottom-up armchair GNR transistors based on the Landauer-Büttiker formalism. A systematic theoretical investigation of single-GNR transistors is carried on, with the consideration of intrinsic and extrinsic effects such as carrier scattering, scaling length, gating efficiency, thermionic field emission, short contact length, source-to-drain tunneling, charging of trap states, and GNR-GNR screening. To further analyze the electrical characterization of multiple-GNR transistors, a Monte Carlo simulation is performed to capture the length and spatial distributions of GNRs as well as the variance of the transport behavior in each GNR. The model shows good consistency with experimental results. This work establishes a solid foundation for in-depth studies of the unique mesoscopic transport properties of different types of GNRs, and for further optimizations of the transistor performance. |
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U71.00098: Probing superconductivity in twisted bilayer graphene Parmeshwar Prasad, Rajashree Haldankar, Johann Osmond, Adrian Bachtold When two graphene lattices are overlapped, they create a moiré pattern with a long superlattice period. At a twist angle around 1.10 also known as magic angle the twisted bilayer graphene stack becomes superconducting.[1] By tuning the carrier density, the twisted bilayer graphene stack becomes an insulator.[2,3] These properties are similar to those of cuprates and other high-temperature superconductors. In this poster, we explain our efforts in fabrication of twisted bilayer graphene devices. |
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U71.00099: Functionalization of graphene with metal nanoparticles by pulsed laserinduced
synthesis Ravina Beniwal, Pratiksha Gawas, Aswathy Sundaresan, Shadak Alee K, Venkatramaiah Nutalapati, Bala Murali Krishna Mariserla The functionalization of two-dimensional atomic crystals with tailored |
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U71.00100: Effect of heat treatment on Oxigen-rich functional groups in multilayer oxide Graphene Adela Aurora Perez, Rocio Amelia Montalvo, Maria Elena Lopez, Ana Champi, Pablo Rivera Riofano Multilayer Oxide Graphene (MOG) with Oxigen-rich Functional Groups (OFG) provides an attractive means to tunning electronic properties of MOG as smell sensor and others interesting applications. |
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U71.00101: Electrically tunable 2D ferromagnetic semiconductors CrSBr and CrSeBr with high Curie temperature Hua Wang, Baiyu Zhang, Xiaofeng Qian Identifying 2D ferromagnets with high transition temperature is crucial for the development of miniaturized spintronics and magnetoelectrics. Here we present our theoretical study of van der Waals layered magnetic semiconductors CrSBr and CrSeBr. Using first-principles DFT and renormalized spin-wave theory, we show that monolayer CrSBr and CrSeBr exhibit highly anisotropic electronic structure with a sizable bandgap. More importantly, monolayer CrSBr and CrSeBr possess high Curie temperature of ~150K which was recently verified by experiments, beyond that of CrI3 and Cr2Ge2Te6. The origin of the high Curie temperature is attributed to strong anion-mediated superexchange interaction and sizable spin-wave excitation gap due to large exchange and single-ion anisotropy. It was shown that electrostatic doping can switch magnetization easy axis, realizing spin field effect transistor. Monolayer CrSBr and CrSeBr semiconducting ferromagnets offer long-desired alternatives to dilute magnetic semiconductors and provide unprecedented opportunities for 2D spintronics such as spin valves and spin FETs. Reference: APL 117, 083102 (2020). |
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U71.00102: First-Principles Theory and Insights of 2D Ferroelectric Semiconductors and Semimetals Xiaofeng Qian Nanoscale ferroelectrics hold promises for many miniaturized devices. Here we present first-principles prediction and understanding of three 2D ferroelectrics, including (a) semiconducting 2D group IV monochalcogenides [1], (b) semiconducting 2D multiferroic semiconductors in monolayer transition metal phosphorus chalcogenides (TMPCs) with coexisting ferroelectricity and ferromagnetism [2], and (c) semimetallic few-layer WTe2 [3,4]. Monolayer group IV monochalcogenides hold anisotropic and large ferroelectric polarization with visible-spectrum excitonic gap, sizable exciton binding energy and strain-tunable ferroelectric transition barrier. In contrast, monolayer TMPCs hold coexisting ferroelectricity and ferromagnetism with out-of-plane electric polarization, suggesting the possibility of controlling polarization by external electric field. Finally, we show that ferroelectric polarization in few-layer WTe2 is originated from interlayer sliding, enabling facile ferroelectric switching upon electric gating demonstrated in experiment very recently [4]. References: [1] 2D Materials 4, 015042 (2017). [2] APL 113, 043102 (2018). [3] npj Comput. Mater. 5, 119 (2019). [4] Nat. Phys. 16, 1028-1034 (2020). |
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U71.00103: Epitaxial Graphene Microstructures as Electron Emission Sources Towards Emission of Soft X-rays Daniel Lewis, Kevin Daniels Electron emission sources are of critical importance in imaging applications, most especially in electron microscopy and X-ray generation. Graphene nanostructures, crafted by CVD, arc discharge, or exfoliation, have been shown to exhibit electron emission under bias, with theoretical outputs exceeding thermionic or field emission sources of similar dimensionality and applied bias conditions. With even low applied bias (3 - 5 V) nanoribbons suspended in high vacuum exhibited phonon-assisted electron emission, resulting in nA emission currents at internal electric fields and external pulling voltages both nearly 100x less than comparable thermionic or field emission sources. Simulations for epitaxial graphene microstructures have shown the potential for emission sources over 10000x larger, with emission currents as high as mA at comparable pulling voltages. Fabrication is easily accomplished with minimal contact photolithography steps and plasma etching, ensuring the preservation of the graphene surface and allowing for device control mechanisms that are simpler and more robust than those presented in referenced works. Presented here is a treatment of the preparation, fabrication, and testing of these epitaxial graphene microstructure electron emission arrays. |
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U71.00104: Study of excitonic gas within InAs/Al0.2Ga0.8Sb based broken gap QW system Mehdi Pakmehr, Mohammad Gholami InAs/GaSb based heterostructure known to be a broken gap type-II quantum well (QW) system, possibly hosting 2D case of topological insulating material. We investigated InAs/Al0.2Ga0.8Sb type-II QW system features with the purpose of understanding the reasons behind the measured signals from such a sample through THz magneto-photoresponse spectroscopy at low magnetic field region (0.5<B<1.5 T) at cryogenic temperature (1.4 K). The 10 nm thick InAs QW sandwiched asymmetrically between Al0.2Ga0.8Sb layers (as shown in Fig.1) has a sheet density of 7.33×1011 cm-2. Due to band alignment for such a QW system there exist a possibility of forming excitonic gas at the interface layers [1] which could ultimately change the properties of 2DEGs confined within QW system. Through solving 8×8 Kane model Hamiltonian of such a system including all the related effective mechanisms (including strain, SOC) experimental results have been analyzed. We plan to present our findings for the InAs/Al0.2Ga0.8Sb based heterostructure at coming APS march meeting. |
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U71.00105: The observability of quantum pinch effect in the magnetized Quantum Wires Manvir Kushwaha We investigate a two-component, cylindrical, quasi-one-dimensional quantum plasma subjected to a |
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U71.00106: Exploiting the magneto-optics of quantum wires for designing optical amplifiers Manvir Kushwaha This report aims at a core issue related with the magnetoplasmon excitations in the quantum wires |
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U71.00107: The magneto-optics in quantum wires comprised of vertically stacked quantum dots: A call for the magnetoplasmon qubits Manvir Kushwaha We embark on the collective excitations in a quantum wire made-up of vertically stacked, self-assembled InAs/GaAs |
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U71.00108: Characteristic Lengths of Interlayer Charge-Transfer in Correlated Oxide Heterostructures Ganesh Ji Omar, Ariando Ariando Using interlayer interaction to control functional heterostructures with atomic-scale designs has become one of the most effective interface-engineering strategies nowadays. Here, we demonstrate the effect of a crystalline LaFeO3 buffer layer on amorphous and crystalline LaAlO3/SrTiO3 heterostructures. The LaFeO3 buffer layer acts as an energetically favored electron acceptor, resulting in modulation of interfacial carrier density and hence metal-to-insulator transition. For amorphous and crystalline LaAlO3/SrTiO3 heterostructures, the metal-to-insulator transition is found when the LaFeO3 layer thickness crosses 3 and 6 unit cells, respectively. Such different critical LaFeO3 thicknesses are explained in terms of distinct characteristic lengths of the redox-reaction-mediated and polar-catastrophe-dominated charge transfer, controlled by the interfacial atomic contact and Thomas-Fermi screening effect, respectively. Our results not only shed light on the complex interlayer charge transfer across oxide heterostructures but also provides a new route to precisely tailor the charge-transfer process at a functional interface. |
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U71.00109: High-throughput focused ion beam platform for deterministic single ion implantation Michael Titze, Anthony Flores, George Burns, Edward Bielejec Single ion implantation is of interest for a wide range of quantum applications, such as quantum communication, computation and sensing. Implantation of single ions allows creation of donor qubits in Si or creation of optically active defect centers, for example SiV in diamond. However, the number of ions implanted is governed by the Poisson distribution. While at high doses, the spread of the Poisson distribution about its mean value becomes negligible, when implanting a single ion, the two failure modes of implantation of no ion or more than one ion exceed the probability of implanting one ion. In order to enable high-throughput creation of quantum devices, it is necessary to deterministically implant single ions with high spatial resolution. Using a focused ion beam system, spot sizes of 10s of nm can be achieved, sufficiently small for most quantum applications. To enable deterministic implantation of single ions, the sample to be implanted is turned into a detector, enabling detection of ions with near 100% efficiency. To implant single ions, the ion beam is pulsed onto the sample for short periods of time and immediately interrupted once an ion strike has been detected on the sample. |
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U71.00110: Fabrication, characterization, and thermal conductivity reduction of freestanding phononic crystal membranes via block-copolymer directed-self assembly Elizabeth Ashley, Naoki Tambo, Marcello Puligheddu, Masaki Fujikane, Paul F Nealey Block-copolymer (BCP) directed self-assembly (DSA) is a valuable technique that enables formation of defect-free, single crystal nanostructures over large areas. This is accomplished via a chemical template patterned via ebeam lithography. For perpendicularly oriented cylinder-forming BCPs, which spontaneously form a polycrystalline hexagonally close-packed lattice, controlling the orientation of the DSA pattern enables direct control of the in-plane lattice orientation, total pattern area, and number of periods. For BCPs such as PS-PMMA, the nanostructures can be transferred into an inorganic substrate, such as Si, and integrated into fabrication process flows for complex devices. Here, we present a methodology for integrating cylinder forming PS-PMMA DSA with a novel fabrication process to produce freestanding nanoporous Si membranes that scatter heat-carrying phonons. By controlling the orientation of the lattice, a line-of-sight heat transport pathway can be ope |
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U71.00111: Towards Magnetically Tunable Extraordinary Optical Transmission Silverio Johnson, Mark Yu, Petr Moroshkin, Richard Osgood, Jimmy Xu Extraordinary optical transmission (EOT) is the transmission of electromagnetic radiation through an |
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U71.00112: Multi-Layered Structures for Low-Temperature Low-Energy Optical Interconnects for Quantum Computers Shaina Raklyar, Patrice Prosper, Jorge Bermeo, German Kolmakov Connecting quantum computers with the end user is challenging technological problem due to the energy consumption and high data rate requirements. We propose a design of a linearly shaped electrically controlled optical switch based on the studies of propagation of an exciton-polaritons in a quasi-2D, patterned optical microcavity with an embedded semiconducting quantum well. The polaritons are driven by a time-dependent drag force owing to the interaction of neutral or charged excitons (the matter component of polaritons) in a quantum well with the electric current running in the structure. Polaritons are generated due to laser pumping with Gaussian distribution of power in the beam. In our poster, we present our findings and, in particular, we discuss how operating frequency of the electrically controlled optical switch depends on the heterostructure material composition, length of the channel, duration of the drug pulse, and other parameters of the system and estimate the magnitude of such operating frequency. |
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U71.00113: Hybrid Magneto Photonic Material Structure for Plasmon Assisted Magnetic Switching Alan H Chu, Bradlee Beauchamp, Deesha Shah, Aveek Dutta, Alexandra Boltasseva, Vladimir M Shalaev, Ernesto Marinero We have proposed the use of surface plasmon resonances at the interface of hybrid magneto-photonic heterostructures [Opt. Mat. Exp., 7, 4316 (2017)] for all-optical control of the macroscopic spin orientation in nanostructures in fs time scales. This requires strong spin-photon coupling for the resonant enhancement of opto-magnetic fields, generated through the inverse Faraday effect, in magnetic nanostructures with perpendicular anisotropy. Here we report on the development of nm thick interlayers to control the growth orientation of hcp-Co alloys grown on refractory plasmonic materials to align the magnetic axis out-of-plane, thereby meeting key requirements for the realization of ultrafast magneto-photonic devices. |
(Author Not Attending)
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U71.00114: Confined terahertz waves for dynamical modulation of material properties Mattias Matthiesen Control of material properties (e.g. critical temperatures, magnetization, conductivity tensor), are regularly achieved with methods such as pressure, strain and electromagnetic fields. It is desirable to extend this degree of control to high frequencies. In an ongoing research effort, solids are excited in the terahertz (1012 Hz) with new intense terahertz photon sources, exploiting this interesting band which lies at the edge of quasistatic approximations, intermediating between static control of matter and resonant interaction with low-energy modes. In an alternative approach, rather than using intense sources, I will use the idea of spatial confinement to enhance the coupling of terahertz drives (photons or phonons) to solid properties. Tailored cavities for photons and phonons will serve to amplify and tune their fields, with the aim of modulating macroscopic properties at faster timescales and larger amplitudes than conventionally possible. |
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U71.00115: Excitation of dark mode in high-index dielectric oligomer nanostructures Brighton Xander Coe, Mahua Biswas, Uttam Manna Resonant optical excitation of high index dielectric nanoparticles offers unique opportunities for reduced dissipative (non-radiative) losses and large resonant enhancement of both the electric and magnetic near-fields. However, they still suffer from radiative losses. One could possibly inhibit the radiative losses in dielectric nanostructures by excitation of dark modes. Here, we use Cylindrical Vector Beams with spatially variant polarization properties to excite dark modes in symmetric dielectric oligomers by breaking the symmetry of the nanostructures. |
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U71.00116: Synthesis and magnon thermal transport properties of spin ladder Sr14Cu24O41 microstructures Xi Chen, Jaehyun Kim, Qianru Jia, Sean E Sullivan, Youming Xu, Karalee Jarvis, Jianshi Zhou, Li Shi Recent experiments on Sr14Cu24O41 bulk single crystals have revealed a remarkable magnon thermal conductivity. Although Sr14Cu24O41 crystals have been grown and studied extensively, there have been few reports on the synthesis and magnon thermal transport investigation of their microstructures. Here, we report the synthesis and thermal transport properties of Sr14Cu24O41 microrods. These microrods synthesized by a co-precipitation method are single crystals grown preferentially along the ladder axis. Based on a four-probe thermal transport measurement, the thermal conductivity of the microrods reveals appreciable magnon transport in the microstructures. According to a kinetic model analysis, magnon transport in the microrods is suppressed mainly by increased point defect scattering compared to the bulk crystals, whereas surface scattering is negligible for anisotropic one-dimensional magnon transport along the ladder. Moreover, the thermal conductivity is enhanced after annealing as a result of reduced oxygen vacancies. These results provide useful insight on the transport of heat and quantum information based on quantum micro- and nanostructures. |
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U71.00117: Topological quantum thermocouple Marco Antonio Jimenez Valencia, Charles Stafford The thermoelectric properties of an open quantum system consisting of two quantum dots coupled to three macroscopic electron reservoirs are investigated. The heat and charge currents are shown to be topologically reshaped by the Aharonov-Bohm effect. The optimal parameters for the maximum cooling of a probe are studied. An exploration of persistent currents present in the system is discussed and contrasted with classical thermodynamics and an apparent paradox involving persistent Peltier cooling in equilibrium is resolved by a rigorous treatment of heat flow at the quantum level. |
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U71.00118: Enhanced Absorption of Extended Short-Wave Infrared in GeSn Nanowire arrays Anis Attiaoui, Étienne Bouthillier, Gerard Daligou, Aashish Kumar, Simone Assali, Oussama Moutanabbir Engineering light absorption in GeSn structures is crucial to enhance their basic device performance for a variety of applications such as MIR photodetectors. Since Group IV semiconductors typically have large refractive indices compared to air, planar opto-electronic devices are plagued by this refractive index mismatch. A promising method to circumvent this limitation is the use of semiconductor nanowires (NW) arranged in arrays. Top-down etched GeSn NW arrays were microfabricated with varying geometrical configuration. Detailed finite difference time domain (FDTD) simulations were combined with experimental analyses to systematically investigate light-GeSn NW interactions. The diameter-dependent leaky mode resonance peaks are theoretically predicted and experimentally confirmed with a tunable wavelength from 1.5 to 2.2 μm. A three-fold enhancement in the absorption with respect to GeSn thin film at 2.1 µm was achieved using NWs with a diameter of 325 nm. Coupling between the HE11 and HE12 resonant modes manifests at NW diameters above 325 nm and explains the observed absorption enhancement. The ability to manipulate light-matter interactions at the nanometer scale with GeSn is opening up new opportunities for spectral tunability in the extended short-wave infrared range. |
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U71.00119: Effect of nanoclay on epoxy nanocomposites Suresh Ahuja Nanoclays are nanoparticles of layered mineral silicates with layered structural units that can form complex clay crystallites by stacking these layers. Nanoclay stacks are fully separated by polymer chains in the exfoliated structure, providing superior mechanical properties and polymer processability. There are three major synthesis procedures for polymer/nanoclay composites including the melt-blending method, solution-blending method and in-situ polymerization method In our method of making nano-composites, an epoxy, diglycidyl ether of bisphenol A (DGEBA) was mixed with different organically modified montmorillonite nanoclays under high shear. A model of visco-elastic deformation is presented which predicts linear to non-linear visco-elastic deformation dependent on the density and spacing of the silicate layers. On dependence of filler on epoxy nano-compisites, Cloisite nanocomposites show power law dependence on elastic and viscous modulus. Temperature dependence on the nano-composite appears to depend on the structure of the organic clay and its flexibility. |
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U71.00120: 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, Zach Biegler, Hadley Smith 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 (10-10) 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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U71.00121: Simultaneous Oxygen and Light Exposure Induced degradation of MAPbBr3 KE WANG, Benjamin Ecker, Jinsong Huang, Yongli Gao In this work, we investigated oxygen and light induced the degradation on methylammonium lead bromide (MAPbBr3) single crystal by using X-ray photoelectron spectroscopy (XPS). The elemental core level spectra show substantial surface degradation during the exposure. It was found that the with light the oxygen degradation process of the MAPbBr3 was substantially accelerated. Quantitative analysis showed that Carbon, Bromine and Nitrogen lost 52%, 56% and 90% of their initial concentration respectively at 1012 Langmuir of oxygen exposure. It further showed that ~11% of the perovskite’s Pb degraded to metallic Pb at 109 Langmuir. We observed that the new metallic Pb component faded away and the oxygen peak started to form after 1011 L, which indicates the oxidation of metallic Pb with the increase of the oxygen pressure. |
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U71.00122: Density Functional Theory Calculations of Al doped Hafnia for Distinct Crystal Structure Configurations Joshua Steier, Mehmet Alper Sahiner, Rory Vander Valk, Jared Savastano, Stephen P Kelty Thin films of Hf based oxides gained importance after the discovery of the ferroelectricity in these materials. Ferroelectricity is typically exhibited in non-volatile memory devices and is largely impacted by the crystal structure. One of the ways to achieve ferroelectricity in HfO2 is doping with metals such as Zr and Al to modify the crystal structure towards orthorhombic symmetry. In Hf based oxide thin films prepared by doping, multiple crystal phases could emerge. In this work, we theoretically investigated the stability of the possible structures that could be present in Al doped HfO2 using quantum mechanical methods. Specifically, using plane wave density functional theory, the monoclinic, tetragonal, orthorhombic, and rhombohedral phases of aluminum doped hafnia were geometrically optimized. The resulting optimized structures for 3%, 6%, and 7% Al doped hafnia structures will be used as theoretical reference structures for EXAFS spectra obtained Al doped HfO2 thin films |
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U71.00123: The Nature of Extremely Large Nonsaturating Magnetoresistance in SrNbO3-SrTiO3 System Jie Zhang, Jong Mok Ok, Hu Miao, Ho Nyung Lee Understanding unconventional magnetoresistance (MR), such as negative longitudinal MR and non-saturating linear MR (LMR), gives deep insight into the electronic processes in a wide range of quantum materials including compensated semimetals, metals, and topological materials. However, the connection between MR and non-trivial topology is unclear. In this work, we observe LMR as high as 150,000% in the SrNbO3-SrTiO3 system with carrier density n~1021 cm-3 and show that the LMR is a direct consequence of the high mobility of the coherent electronic system. By tuning the carrier density over two orders of magnitude via thickness control and tracking the onset field and temperature dependence of LMR, we find results are consistent with the semiclassical guiding center model [1]. Under this framework, the guiding centers travel along the equipotential lines of weakly disordered potentials while remaining coherent. A brief discussion along with the data will be presented in the talk. |
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U71.00124: Phase-Field Crystal Modeling of Materials Structural Evolution in the Presence of Pores Abash Sharma, Ebrahim Asadi, Mohamed Laradji The presence of pores in materials plays an important role on the evolution their microstructure and can significantly affect their mechanical properties including their fatigue life. We formulate a continuum approach, based on phase-field crystal (PFC) model to numerically investigate the effect of nanoscale pores in two-dimensional materials. We found that nanoscale pores act as a nucleation agent promoting crystallization at the interface between the material and the pore, followed by dendritic growth of the crystal in the supercooled liquid. Detailed results of the effects of the pore's geometry and size, and interfacial tension between the material and the pore, on the crystallization of the material will be presented and discussed. |
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U71.00125: Phase Transformation by Superoxygenation in Cuprate and Iridate Thin Films Chao Zhang, Hao Zhang, Nicolas Gauquelin, Shaobo Cheng, Gianluigi Botton, Christopher McMahon, David Geoffrey Hawthorn, Patrick Clancy, Saehwan Chun, Young-June Kim, Ambrose Seo, John Y.T. Wei High-pressure O2 has previously been used to hole-dope and stabilize high-oxidation phases of cuprates. We extend this superoxygenation technique to materials in thin film form since they are more reactive due to their large surface-to-volume ratio. YBa2Cu3O7-δ (YBCO) thin films grown by PLD are annealed in up to 700 atm O2 and then characterized by TEM, XRD and XAS. The annealed films show phase conversion to Y2Ba4Cu7O15-δ and Y2Ba4Cu8O16, as well as regions well as regions of YBa2Cu5O9-δ and YBa2Cu6O10-δ. Epitaxial thin films of Sr2IrO4 are subjected to extended high-pressure annealing and similarly characterized. The post-annealed films show up to 3 order-of-magnitude drop in room temperature resistivity and an evolution towards semi-metallic behaviour. Furthermore, as film thickness is reduced, the annealed films show a structural transformation towards a quasi-cubic phase. Our results demonstrate the potential of using superoxygenation to stabilize exotic phases of transition metal oxides not achievable in bulk form and to create novel materials by selectively transforming constituent layers in multilayer films. [1] |
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U71.00126: Investigating the anharmonic lattice dynamics of tin sulfide using DFT and molecular dynamics simulations Elise Koskelo, Quinn M White, Yanbing Zhu, Evan J. Reed, Daniel Sheppard, Ann E Mattsson, Daniel Rehn Monolayer SnS exhibits two phases with similar crystal structures and low thermal conductivities, making it a promising candidate for phase change memory and thermoelectric applications. The high temperature square phase (single layer of the bulk Cmcm crystal) can be described as a thermal average of two degenerate configurations of the low temperature rectangular phase (single layer of the bulk Pnma crystal). In this work, we investigate the lattice dynamics of monolayer SnS to probe the thermally induced transition between phases. Using a frozen phonon approach with density functional theory (DFT), we confirm the existence of a displacive phase transition associated with strong anharmonicities of the square phase. To further understand the phase transition dynamics, we conducted DFT-based molecular dynamics (MD) simulations at finite temperature. Using the MD results, we estimate the free energy and thermal conductivity of the phases via the Temperature Dependent Effective Potential (TDEP) method. We find a strong dependence of the zero stress lattice parameters on the temperature, highlighting the importance of finite temperature effects in the study of the anharmonic phase transition dynamics of monolayer SnS. |
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U71.00127: Physical and Electrochemical Properties of the LiCoO2/LiMn2O4 Interface in Lithium-Ion Batteries Erica Wiley, Mehmet Alper Sahiner, Jai Patel, Kellen Murphy Lithium-Ion batteries are currently widely used in many applications. . This is due to their high-power density and high energy. Improvements for Lithium-Ion batteries will mean improvements in everyone’s present lives. One way to improve the performance of Li-ion batteries is by decreasing the internal resistance of the Lithium-Ion electrode/electrolyte interface. The result will be a more efficient exchange of charge in the battery. One way we might decrease impedance is to investigate the physical and electrochemical properties of Pulsed Laser Deposited LiCoO2 and LiMn2O4 onto Polished Pt substrate at various deposition conditions such as laser energy, frequency, substrate temperature. We will be measuring the thickness of the films using an Ellipsometer and resistivity using the 4-point probe. We will be doing imaging of the films via Scanning Electron Microscopy (SEM) and analyzing chemical composition using Energy Dispersive X-Ray Analysis (EDX). |
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U71.00128: Concentration-dependent surface electronic properties and modification of vibrational properties in graphene-hBN nanocomposites. Tanmay Mahanta Graphene opens up the possibility of miniaturization of devices and many new materials follow it after its finding. It possesses remarkable properties such as high electrical conductivity, zero bandgaps etc. However, to harness graphene completely in technological fields, we've to be able to alter its fundamental characteristics in the desired direction. The zero bandgaps metallic character is not suitable for its use in making electronic devices. The work function too should be controlled to make optoelectronic devices and to be used in solar cells. In an attempt to open up its bandgap, we made nanocomposites of hexagonal boron nitride(hBN) and graphene and explored the surface electronic properties and vibrational properties of the same. Besides the opening of bandgap which was detected with Uv-Vis spectroscopy, we perceived that the doping effect comes to play which leaves its sign in Raman spectra and surface potential mapping, that alters its work function too. For the Raman spectroscopy, we've employed Witec model alpha 300 and SKPM(Scanning Kelvin Probe Microscopy) of KP Technology was used to map the contact potential difference. |
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U71.00129: Computational Structure Prediction for Interfaces: What is Currently Possible? Fabio Calcinelli, Johannes Cartus, Lukas Hörmann, Andreas Jeindl, Anna Werkovits, Oliver Hofmann Studying the electronic structure of organic monolayers on metals requires knowledge about their atomistic structure. Such monolayers display rich polymorphism arising from diverse molecular arrangements. The large number of possible orientations and motifs poses a big challenge for determining the different polymorphs from first principles. To meet this challenge, we develop SAMPLE[1], which employs coarse-grained modeling and machine learning to efficiently map the minima of commensurate organic adlayers. With a few hundred DFT calculations as input, we use Bayesian linear regression to determine the parameters of a physically motivated energy model. These parameters yield meaningful physical insight and allow predicting adsorption energies for millions of possible polymorphs with high accuracy. |
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U71.00130: A route to atomically flat TiO2 terminated surfaces in SrTiO3 avoiding HF acid Dakota Brown, James Alan Payne, Maitri P 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 acid1 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 once heated to typical film-growth temperatures, this process provides extremely smooth surfaces with very sharp step edges that are mostly oriented parallel to the crystallographic axes. |
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U71.00131: Far-Infrared Spectrum of Free Exciton Transitions under Magnetic Fields Yi Wang, Liuyun Yang, Xinqiang Wang, Changli Yang, Chi Zhang We investigate magneto- far-infrared (FIR) transmission on a 100 nm thick Wurtzite GaN film that is grown on a Si/HR-GaN substrate. Under zero magnetic field (B), we observe three absorption peaks at the energy of 30.6 meV (valley I), 34.7 meV (valley II), and 40.0 meV (valley III), respectively. Under perpendicular B, small energy blue shifts of the three absorptions (I, II, III) are all linear to B. Meanwhile, minimum II splits into two distinct valleys, with a distance of about 0.08 meV/T in between. And three distinct splits are observed around valley III with a distance of about 0.11 meV/T between neighboring peaks. We propose that the absorption patterns can be attributed to the transitions between the energy levels of the fine structure of free excitons in GaN, i.e. the direct transitions between n = 1 (1s) and n = 2 (2p) energy levels under magnetic fields up to 14.5 T. |
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U71.00132: Effect of Anionic Stoichiometry and Composition Variations on the Structural and Electrical Properties of Mixed Valent Manganite Thin Films Benjamin Alan Moore, Caleb Maddux, Francis Frederick Walz, Joseph D Cartelli, Rajeswari Kolagani Thin films of rare earth manganites of the generic composition (RE)1-x(AE)xMnO3 are well known for electronic phenomena such as insulator-metal transitions, charge ordering and colossal magnetoresistance. These phenomena are sensitive to the compositional variations at the RE and AE sites, as well as variations in oxygen stoichiometry, both of which control the Mn valence state distribution. In addition, the structural changes accompanying these compositional changes influence these properties through effects such as Jahn-Teller distortions and local strain fields promoting electronic phase separation. We will present the results of our experiments designed to controllably create oxygen vacancies in epitaxial thin films and partially substitute oxygen by fluorine through a post-deposition heat treatment . We observe structural changes as well as changes in electrical transport properties upon subjecting the films to the fluorination process. These changes will be discussed in the light of possible charge doping and structural changes introduced as a result of the differences in valence state and ionic sizes of oxygen and fluorine. |
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U71.00133: Interaction of aromatic molecules with silica film supported on Ru(0001) using UHV Experiment and DFT William Kaden, Muhammad Sajid, Abdelkader Kara Organic molecules show promising electronic properties for future devices. The performance of organic devices depends strongly on the atomic and electronic properties at the interface with metallic substrate. In order to understand this interface, we chose two simple probe organic molecules (benzene and pyridine) and studied their interaction with Ru(0001) surface, using Density Functional Theory (DFT) with and without decoupling inert silica layer in between. Diffusion characteristics of molecules on and under the thin-film was also analyzed using Nudged Elastic Band (NEB). In order to validate computational predictions, interaction of molecules with silica film was studied using Temperature Programmed Desorption (TPD) and X-ray Photoelectron Spectroscopy (XPS) measurements. Our results from both sources, indicate that the molecules not only physisorb on silica layer rather they also seep through silica film to react with the metal. Through joint venture of theory and experiment, cross-validation of results is obtained. |
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U71.00134: Quantum-mechanically informed model of dynamic precipitation in MgAl alloys Swarnava ghosh Precipitates are ubiquitous in metallic alloys and play a vital role in strengthening by blocking the motion of dislocations. The size and shape of these precipitates are important. The amount of hardening depends critically on the number density and orientation. Furthermore, they also can contribute to the lack of ductility, fracture and fatigue, and reduced spall strength and creep when their sizes become too large. Therefore, it is of active interest to control the size of these alloys. Unlike precipitates formed due to aging, dynamic (stress induced) precipitation give rise to small precipitate sizes. We present a quantum-mechanically informed strain, concentration and temperature dependent free energy functional for dynamic precipitation in MgAl alloys [1]. We discuss the influence of various conditions of stress and temperature on the microstructure and its consequences. |
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U71.00135: Metal-Insulator Transition and Doping-Induced Phase Change in Ge2Sb2Se5xTe5-5x Zhenyang Xu, Keeseong Park, John Schneeloch, Despina A Louca A phase change material (PCM), Ge2Sb2Te5 (GST-225), with vast differences in the electrical and optical characteristics between its amorphous and crystalline phases, is revisited to explore its properties with Se doping. GST has a layered hexagonal ground state, while the precursor to the amorphous state is a distorted rock-salt like structure with vacancies at the Ge/Sb sites. Upon Se doping, liquid nitrogen quenched Ge2Sb2Se5xTe5-5x (GSST-225) exhibit a direct hexagonal-to-amorphous phase change above x > 0.8. The rock-salt like structure appears as a second phase with its volume fraction that does not change as a function of the doping. The phase change is accompanied by a metal-to-insulator transition (MIT), with several orders of magnitude increase in the resistivity on approaching the amorphous state. On warming amorphous GSST (x = 0.9) above room temperature, a reversal to the crytsalline hexagonal phase occurs with a re-crystallization onset temperature (Tc) above 300 degree, much higher than the Tc (around 170 degree) of amorphous GST and an activation energy of 1.47 eV, which is comparable to good glass formers. |
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U71.00136: Structural, electromagnetism and elastic properties of Mn3Sb Balaram Regmi, Gopi Kaphle, Durga Paudyal We unraveled here the ferromagnet, pseudo-gap and topological behavior of Mn3Sb in DO3 Heusler structure. This compound shows unique structural, electronic, magnetic and elastic properties. The structure and Density of States (DOS) shows the characteristics of band topology with pseudo-gap. The calculated elastic constants, bulk to shear modulus ratio, and elastic anisotropy indicate that Mn3Sb is mechanically stable, ductile, and elastically anisotropic, respectively. |
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U71.00137: Symmetry Breaking in a Polar Metal Probed with XUV Second Harmonic Generation Emma Berger, Sasawat Jamnuch, Can Uzundal, Clarisse Woodahl, Hari Padmanabhan, Angelique Amado, Paul Manset, Yasuyuki Hirata, Iwao Matsuda, Venkatraman Gopalan, Yuya Kubota, Shigeki Owada, Kensuke Tono, Makina Yabashi, Craig Schwartz, Walter Drisdell, John Freeland, Tod Pascal, Michael Zuerch It was first predicted over 50 years ago that polar metals could form through a 2nd order phase transition, but the first experimentally realized polar metal, LiOsO3, was discovered only recently [1]. In LiOsO3, a continuous phase transition occurs at Tc = 140 K, where it transitions from a nonpolar metallic to a polar metallic phase through the loss of inversion symmetry. Previous measurements have shown that the transition involves a coordinated 0.5 Å displacement of Li-ions along the polar axis. To gain insight into the nature of the Li-coordination environment in the polar phase, we turn to extreme ultraviolet second harmonic generation (XUV-SHG) at a free electron laser (XFEL). Here, we directly probe the dielectric environment around the Li-ion below Tc by tuning the incident XFEL energy to be half-resonant with energies around the Li K-edge [2]. We extract the effective X(2) and use ab initio simulations to relate the nonlinear response to the Li coordination environment. Our results provide insight into the Li-bonding environment and pave the way for future ultrafast time-resolved studies of phase transitions involving structural distortions. |
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U71.00138: Fatigue Analysis Based on the Field Theory of Deformation and Fracture Conor McGibboney, Sanichiro Yoshida, Naoya Fujishima, Shun Takahashi, Tomohiro Sasaki We are developing a physics-based numerical model for fatigue using the Field Theory of Deformation and Fracture (Field Theory). The interferometric technique Electronic Speckle-Pattern Interferometry (ESPI) is used to analyze the spatiotemporal behavior of the displacement field formed while a specimen experiences cyclic loads. Numerical models solve wave equations derived from the Field Theory under conditions assimilated with physical experiment. The Field Theory describes deformation dynamics of elastic, plastic, and fracture stages, using the same theoretical foundation. Hence, the Field Theory defines each stage with specific spatiotemporal features. The ESPI experiment exhibits these features at each stage with corresponding fringe patterns that are consistent with stress-strain characteristics. The numerical results exhibit similar spatiotemporal behavior of the displacement field observed in experiment in the respective stages. Fringe patterns in numerical analysis and experiments are the same in the x and y directions prior to fracture, which is one of the spatiotemporal features defined by the Field Theory. Thus, we can verify that the Field Theory can be used to model fatigue fracture dynamics. This makes the theory useful for aerospace engineers to study fatigue. |
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U71.00139: Rapid design of high-strength refractory alloys for high-temperature application Prashant Singh, Duane D. Johnson High-entropy alloys (HEAs) often show excellent mechanical properties (e.g. yield-strength and ductility). Yet, development of new HEAs with useful or improved underlying properties requires exhaustive search of composition space, a bottleneck in computational design. To overcome this, we design a rapid-design approach using density-functional theory within mean-field theory to estimate strain and temperature-dependent strength using DFT-calculated parameters, such as alloy lattice parameters, elemental misfit volumes, and elastic constants. The predicted room-temperature compressive strength of TaWNbMo (0.98 GPa) and TaWNbMoV (1.16 GPa) is in excellent agreement with experiments (1.02 GPa; 1.25 GPa). The proposed approach is used to down select compositions that show improved high-strength at elevated temperature, useful for high-temperature applications. |
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U71.00140: Magnetic, thermodynamic, and electrical transport properties of AlFe2B2 based intermetallic compounds Devanshi Malaviya, MD SAKHAWAT HOSSAIN HIMEL, Mahmud Khan, Arjun Pathak Transition metal borides attracted considerable attention to the scientific community due to its potential applications, including a permanent magnet and cooling devices. AlFe2B2 is one such material that was initially reported by Jeitschko et al. (Acta Crystallogr., Sect. B: Struct. Sci, 25 (1969) 163). Recently, a large magnetocaloric effect near room temperature (Tan et al. JACS 135 (2013) 9553) was reported for the material. The crystal structure of AlFe2B2 based compounds adopts orthorhombic (space group Cmmm) with alternating Al monolayers and Fe2B2 slabs along the long b axis. Here we present the detailed study of the effect of substitution Fe by other 3d elements and B by p-block elements on magnetic, specific heat, and electrical transport properties of AlFe2B2 compound. We observed anomalous electrical transport behavior above and below the ferromagnetic to paramagnetic phase transition and transition temperature can be controlled by substitution. |
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U71.00141: MAGNETISM
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U71.00142: Demonstration and quantitative characterization of effective random exchange fields in ferromagnet/antiferromagnet bilayers Guanxiong Chen, Sergei Urazhdin It was conjectured over 30 years ago that some of the unusual magnetic properties of ferromagnet/antiferromagnet bilayers are associated with the effective random field arising due to the frustration of exchange interaction at their interface [1]. This conjecture was supported by recent measurements demonstrating a correlated spin glass state in these systems [2], but has not yet been directly confirmed. |
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U71.00143: Low-temperature Magnetization Dynamics in Shandite-type ferromagnet Co3Sn2S2 VIPIN NAGPAL, Satyabrata Patnaik We report on the comprehensive anisotropic magnetic properties of shandite-type ferromagnet Co3Sn2S2 single crystals. The low temperature glass-like magnetic behaviour is observed in magnetization measurements. The inverse susceptibility exhibits a sharp downturn and non-linearity close to critical temperature Tc in the paramagnetic region implies the short-range ferromagnetic clusters present above Tc in Co3Sn2S2. The deviation from linear Curie-Weiss behaviour in the paramagnetic state signifies the strong Griffiths singularity in the material. The magnetic hysteresis loops unveil the coexistence of two-phase magnetic systems in Co3Sn2S2. The Arrott plots (M2 vs. H/M) results prove the second phase order transition in Co3Sn2S2. The spin fluctuation theory study confirms itinerant ferromagnetism in Co3Sn2S2. |
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U71.00144: Large field-like torque in amorphous Ru2Sn3 originated from the intrinsic spin Hall effect Thomas Peterson, Mahendra DC, Yihong Fan, Junyang Chen, Delin Zhang, Hongshi Li, Jianping Wang We investigated temperature dependent current driven spin-orbit torques in magnetron sputtered Ru2Sn3 (4 and 10 nm) /Co20Fe60B20 (5 nm) layered structures with in-plane magnetic anisotropy. The room temperature damping-like and field-like spin torque efficiencies of the amorphous Ru2Sn3 films were extracted to be as large as 0.14 ± 0.008 and -0.2 ± 0.009, respectively. The observed room temperature field-like torque efficiency in Ru2Sn3 (10 nm)/CoFeB (5 nm) is up to three times larger than the damping-like torque (-0.20 ± 0.009 and 0.07 ± 0.012, respectively) and thirty times larger at 50 K (-0.29 ± 0.014 and 0.009 ± 0.017, respectively). The temperature dependence of the field-like torques are unique and show dominant contributions from the intrinsic spin Hall effect with intrinsic spin conductivity up to -240 ± 19 (Ωcm)-1 while the damping-like torques show dominate contributions from the extrinsic spin Hall effects with sum of the skew scattering and side jump up to -175 ± 19 (Ωcm)-1. Through macro-spin calculations, we found that including field-like torques on the order or larger than the damping-like torque can reduce the switching critical current and the switching time for a perpendicular ferromagnetic layer. |
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U71.00145: Gapless quantum spin liquid and global phase diagram of the spin-1/2 J1-J2 square antiferromagnetic Heisenberg model Wen-Yuan Liu, Shoushu Gong, Yu-Bin Li, Didier Poilblanc, Wei-Qiang Chen, Zhengcheng Gu We use the state-of-the-art tensor network state method, specifically, the finite projected entangled pair state (PEPS) algorithm, to simulate the global phase diagram of spin-1/2 J1-J2 Heisenberg model on square lattices up to 24 × 24. We provide very solid evidences to show that the nature of the intermediate nonmagnetic phase is a gapless quantum spin liquid (QSL), whose spin-spin and dimer-dimer correlations both decay with a power law behavior. There also exists a valence-bond solid (VBS) phase in a very narrow region 0.56 ≤ J2/J1 ≤ 0.61 before the system enters the well known collinear antiferromagnetic phase. We stress that our work gives rise to the first solid PEPS results beyond the well established density matrix renormalization group (DMRG) through one-to-one direct benchmark for small system sizes. Thus our numerical evidences explicitly demonstrate the huge power of PEPS for solving long-standing 2D quantum many-body problems. The physical nature of the discovered gapless QSL and potential experimental implications are also addressed. (see arXiv:1908.09359 and arXiv:2009.01821) |
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U71.00146: Exact Diagonalization on Pyrochlores CHEN WEI Exact diagonalization is a powerful method to analyze a crystal system. In our research, we apply the exact diagonlization method on 16 site spin 1/2 Pyrochlore system. The Hamiltonian of this system can be expressed as a 65536 times 65536 matrix, then we use point group D_3 and FCC translational group to block diagonalise this matrix. Finally, we apply Lapack subroutine to get the eigenvalues and eigenstates of this 16 sites system. Moreover, we also consider a lattice distortion which reduce the full spce group Fd3m to F43m. With small varying of the exchange constants J_{ij}, we can analyze the ground state energy and the total system energy changing through the lattice distortion. Moreover, using the result from exact diagonalization, we are also able to find the quantum entanglement between different sites in the system with lattice distortion. |
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U71.00147: Emergence of Nematic Paramagnet via Quantum Order-by-Disorder and a Pseudo-Goldstone Mode in Kitaev Magnets Matthias Gohlke, Li Ern Chern, Hae-Young Kee, Yong-Baek Kim The appearance of nontrivial phases in Kitaev materials exposed to an external magnetic field |
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U71.00148: Antiferromagnetic phase transition in the S=3/2 hyperkagome manganate Zn2Mn3O8 Suguru Kitani, Hitoshi Kawaji The hyperkagome lattice has attracted much attention due to a 3-dimensional corner-sharing triangle network. Since the discovery of the spin-liquid state of Na4Ir3O8 in 2007, many theoretical studies on hyperkagome antiferromagnets have been published. However, few other model materials have been found. In this presentation, we report a novel hyperkagome antiferromagnet Zn2Mn3O8, where Mn4+ (S=3/2) ions form a hyperkagome network. Magnetic susceptibility and heat capacity measurements for Zn2Mn3O8 found an antiferromagnetic interaction with a Curie-Weiss temperature θCW = -54 K and an antiferromagnetic phase transition at 5.7 K, indicating the presence of the geometrical frustration. These results suggest that Zn2Mn3O8 is the first hyperkagome antiferromagnet to show a phase transition. We will discuss the detailed behavior of this antiferromagnetic transition. |
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U71.00149: Higgs mode in a diluted classical magnet Reece Beattie-Hauser, Thomas Vojta Recent results[1] have shown that the Higgs(amplitude) mode at a disordered quantum phase transition features unusual localization properties. Here, we analyze the Higgs mode in a diluted 3D classical xy-model near the magnetic phase transition. To this end, we calculate the amplitude correlation function and the corresponding scalar susceptibility by means of Monte Carlo simulations. We determine if the Higgs mode is localized, like in the quantum case, or remains extended when the temperature is varied across the critical point. We also test whether the scalar susceptibility fulfills naive scaling(in contrast to the quantum case). |
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U71.00150: Light-Induced Static Magnetization: Nonlinear Edelstein Effect Haowei Xu, Jian Zhou, Hua Wang, Ju Li We theoretically and computationally demonstrate that static magnetization can be generated under light illumination via nonlinear Edelstein effect (NLEE). NLEE is applicable to semiconductors under both linearly and circularly polarized light, and there are no constraints from either spatial inversion or time-reversal symmetry. Remarkably, magnetization can be induced under linearly polarized light in nonmagnetic materials. With ab initio calculations, we reveal several prominent features of NLEE. We find that the orbital contributions can be significantly greater than the spin contributions. And magnetization with various orderings, including anti-ferromagnetic, ferromagnetic, etc., are all realizable with NLEE, which may facilitate many applications, such as unveiling hidden physical effects, creating a spatially varying magnetization, or manipulating the magnetization of anti-ferromagnetic materials. The relationship between NLEE and other magneto-optic effects, including the inverse Faraday effect and inverse Cotton-Mouton effect, is also discussed. |
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U71.00151: The magnetic and magnetocaloric properties of Ni-rich Mn0.5Fe0.5-xNi1+xSi0.94Al0.06 intermetallic system Babajide Akintunde, Arjun Pathak, Prayushi Bhorania, Mahmud Khan Magnetic refrigeration is considered a viable candidate to replace the conventional vapor-gas compression refrigerators due to its high energy efficiency and environmental friendliness. The technology exploits magnetocaloric effect (MCE) exhibited by a special group of materials for its operations. MCE involves the heating and cooling of a magnetic material when exposed to an external magnetic field. A suitable material for application in this technology is desired to exhibit large MCE near room temperature and minimal thermal hysteresis loss. The intermetallic compound Mn0.5Fe0.5NiSi0.94Al0.06 has been reported to exhibit a first order phase transition and large MCE near room temperature. The first order transition in this compound is accompanied by a thermal hysteresis, which is undesirable for practical applications. In this presentation, we will discuss an experimental study performed on a series of Ni-rich Mn0.5Fe0.5-xNi1+xSi0.94Al0.06 compounds. The goal is to explore the effects of partially replacing Fe with Ni on the structural, magnetic, and magnetocaloric properties of the materials. |
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U71.00152: Sharp or smooth crossover from quantum to classical behavior in S/F/S Josephson φ0 junction Gwang-Hee Kim We consider quantum-classical escape-rate crossover of nanomagnets sandwiched between two superconductors called Josephson φ0 junction. Within the frameworks of the instanton technique and the nonlinear perturbation method we obtain the crossover boundary separating the sharp crossover from the smooth one. It is found that the crossover boundary is greatly influenced by the supercurrent as well as the anisotropy constants and the magnetic field. These features are expected to be observable with existing experimental techniques. |
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U71.00153: Unconventional superparamagnetic behavior in the modified cubic spinel compound LiNi0.5Mn1.5O4 Shams Islam, Vikram Singh, K. Somesh, Prashanta K. Mukharjee, Anil Jain, S. M. Yusuf, Ramesh Chandra Nath LiNi0.5Mn1.5O4 features a three-dimensional pyrochlore lattice and exhibits 1:3 cation order of Mn4+ and Ni2+ ions. The intra-sublattice interaction within each Mn4+ and Ni2+ sub-lattice and the inter-sublattice interaction between Mn4+ and Ni2+ sublattices is found to be ferromagnetic (FM) and antiferromagnetic (AFM) respectively. This leads to the onset of a ferrimagnetic transition at TC ∼ 125 K. The reduced values of frustration parameter (f) and ordered moments reflect magnetic frustration due to competing FM and AFM interactions. A detailed critical behavior analysis nearTC reveals that the magnetic phase transition is second order in nature and belongs to the 3D XY universality class. A large magneto-caloric effect is observed with a maximum value of isothermal change in entropy ΔSm ∼ -11.3 J/Kg-K and a maximum relative cooling power of RCP ∼ 604 J/Kg for 9 T magnetic field change. The imaginary part of the AC susceptibility depicts a strong frequency dependent hump at T = Tf2 well below the blocking temperature Tb ∼ 120 K. The Arrhenius behaviour of frequency dependent Tf2 and the absence of ZFC memory confirm the existence of superparamagnetism in the ferrimagnetically ordered state. |
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U71.00154: Effect of reduced particle size on structural and physical properties of CoFe2O4 nanoparticles Taghrid Ali The structure and magnetic properties of CoFe2O4 were investigated. Cobalt ferrite has been synthesized by the citrate – nitrate combustion method. X-ray diffraction analysis (XRD) illustrated a single-phase cubic structure for all the prepared samples. The particle size was found that it strongly depends on the heat treatment. High-resolution transmission electron microscopy (HRTEM) confirmed the formation of nanoparticles with spherical shapes. Fourier Transform Infrared Spectroscopy (FTIR) observed the two characteristic bands of ferrites. The M–H curve provided information regarding the magnetic parameters such as saturation magnetization (Ms) and coercivity (Hc). |
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U71.00155: Domain Structure and Wall Dynamics in High-PMA NiCo2O4 Thin Films Corbyn Mellinger, Guanhua Hao, Xiao Wang, Xuemei Cheng, Rajesh Chopdekar, Xiaoshan Xu The inverse-spinel room-temperature ferrimagnetic NiCo2O4 (NCO) is of increasing interest, due to its demonstrated large perpendicular magnetic anisotropy, sensitivity of magnetic behavior to mixed cation valence, and deviations from ideal inverse spinel stoichiometry. Among the important information still missing about this material’s magnetic behavior from the literature includes information about the exchange interaction and domain structure of the magnetized film. |
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U71.00156: The Role of DFT Approach in Calculations of Magnetocrystalline Anisotropy in α″–Fe16N2 Peter Stoeckl, Przemyslaw Swatek, Jianping Wang The ordered iron nitride phase α″–Fe16N2 is one of most promising candidates for rare earth–free magnets; validation of its magnetic anisotropy is critical to further improve its performance. So far, both experimental measurements (Ku ~ 4.4 × 106 – 1.9 × 107 erg/cc) and computational results (5.0 × 106 – 1.6 × 107 erg/cc) vary; the latter in particular depend strongly on the density-functional theory (DFT) approaches used. To address this issue, the plane-wave DFT code Quantum ESPRESSO was employed to more comprehensively study the effect of different DFT approaches on the system and its magnetocrystalline anisotropy (MCA) energy, particularly the influence of exchange-correlation (XC) functionals (from LDA through GGA+U) and pseudopotential methods, obtaining a range of results Ku ~ 4.0 × 106 – 2.86 × 107 erg/cc. The role and limitations of these approaches are discussed in light of band structure and density-of-state calculations. In addition, further research into the choice of Hubbard U,J parameters and other XC functionals, as well as alloying for increased anisotropy, are planned. |
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U71.00157: Controlling the stripe order in a diluted frustrated magnet Xuecheng Ye, Thomas Vojta We study the spin-density wave (stripe) order in a two-dimensional frustrated Ising model using Monte-Carlo simulations. It is known that spinless impurities can destroy the stripe phase via a random field mechanism because the stripe order parameter breaks a real-space symmetry [1]. Here, we investigate the effect of anisotropic exchange interactions that explicitly break the symmetry between the stripe directions. We demonstrate that weak anisotropies are sufficient to restore the stripe phase and the corresponding phase transition. We discuss implications for the observability of the random-field mechanism in experiments. |
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U71.00158: Enhancing Nanoparticle Diffusion on a Unidirectional Domain Wall Magnetic Ratchet Ralph Stoop, Arthur Straube, Pietro Tierno In this talk I will demonstrate the controlled motion and the enhancement of diffusion of magnetic nanoparticles that are manipulated and driven across a series of Bloch walls within an epitaxially grown ferrite garnet film. We use a rotating magnetic field to generate a traveling wave potential that unidirectionally transports the nanoparticles at a frequency tunable speed. Strikingly, we find an enhancement of diffusion along the propulsion direction and a frequency-dependent diffusion coefficient that can be precisely controlled by varying the system parameters. To explain the reported phenomena, we develop a theoretical approach that shows a fair agreement with the experimental data enabling an exact analytical expression for the enhanced diffusivity above the magnetically modulated periodic landscape. Our technique to control thermal fluctuations of driven magnetic nanoparticles represents a versatile and powerful way to programmably transport magnetic colloidal matter in a fluid, opening the doors to different fluidic applications based on exploiting magnetic domain wall ratchets. |
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U71.00159: Ice Rule and Emergent Frustration in Particle Ice Antonio Ortiz ambriz, Cristiano Nisoli, Cynthia Reichhardt, Charles Reichhardt, Pietro Tierno In this talk I will describe recent experimental results obtained by using artificial particle ice systems, namely interacting paramagnetic colloids gravitationally trapped within lithographic structures. With experiments, theory and simulations, I will demonstrate that in mixed coordination geometries, entropy-driven negative monopoles spontaneously appear at a density determined by the vertex-mixture ratio. Unlike its spin-based analogue, the colloidal system displays a “fragile ice” manifold, where local energetics oppose the ice rule, which is instead enforced through conservation of the global topological charge. The fragile colloidal ice, stabilized by topology, can be spontaneously broken by topological charge transfer. |
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U71.00160: Examining Domain Wall Skyrmions and Domain Wall Substructures in a Pt/Co/Ni/Ir Multilayer System Maxwell Li, Arjun Sapkota, Anish Rai, Ashok Pokhrel, Tim Mewes, Claudia K.A. Mewes, Di Xiao, Marc De Graef, Vincent Sokalski Topologically protected spin textures stabilized by the Dzyaloshinskii-Moriya interaction (DMI) have great potential for nonvolatile memory and neuromorphic computing. Towards this end, chiral domain walls (DW) and 2D skyrmions have been extensively characterized. Magnetic DW skyrmions are a markedly different spin texture that have been theoretically predicted. These DW substructures are 360° transitions of a chiral DW's internal magnetization and are analogous to vertical Bloch lines (VBL). Here, we performed a systematic study of a [Pt/(Co/Ni)M/Ir]N multilayer system using Lorentz TEM where M modulates the DMI strength and N primarily modulates the total thickness of the sample. We find that the formation of hybrid DWs in thicker films inhibit VBLs and DW skyrmions in contrast to the uniform magnetization expected through ultrathin films while DMI strength is found to primarily dictate the DW character. With these observations, we qualitatively formulated a magnetic phase diagram of the domain wall character with respect to DMI strength and film thickness. |
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U71.00161: Predicting and controlling permanent magnet functionalities from theory and computation Durga Paudyal The very first criterion for permanent magnetic material prediction is crystal structure which allows magnetic moments to align along the anisotropic crystal axis. Hexagonal and tetragonal structures do fall within this category. The non-equivalent crystal sites in a complex structure play a key role in determining the magnetic moments, uniaxial magnetic anisotropy, and chemical stability. Employing advanced density functional theory (DFT), which includes electron correlation and spin orbit coupling, we first analyze theoretically predicted intrinsic permanent magnetic properties (magneto-crystalline anisotropy, magnetic moment, and magnetic order-disorder transition temperature) of known model permanent magnetic materials such as Nd2Fe14B, NdFe12N, SmCo5, and Sm2Co17. Next, we present how our electronic structure calculations with site substitution mechanism allow us to reduce critical rare earths and transition elements without affecting intrinsic permanent magnetic properties. |
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U71.00162: Thermodynamics of possible quantum spin liquid state in metal-oxalate framework [(C2H5)3NH]2Cu2(C2O4)3 Charuni Dissanayake, K A M Hasan Siddiquee, RIFFAT MUNIR, Wesley Newsome, Fernando Uribe-Romo, Yasuyuki Nakajima [(C2H5)3NH]2Cu2(C2O4)3, is a three-dimensional metal-oxalate framework that forms a hyper-honeycomb lattice structure. In this lattice, Cu atoms form two distinct zigzag chains perpendicular to each other and offer alternating handedness in both left and right. As a result, this lattice contains two crystallographically distinct sub-lattices of Cu atoms [1, 2]. Jacko et al. suggest that one sub-lattice is strongly dimerized while the other forms isolated isotropic antiferromagnetic (AF) Heisenberg chains with Tomonaga-Luttinger spin liquid ground state [2]. Here we report thermodynamic properties of [(C2H5)3NH]2Cu2(C2O4)3 to characterize the spin liquid ground state. We find a sizable fermionic contribution in the specific heat at low temperatures, suggestive of the presence of a gapless ground state. We will also discuss the magnetic field dependence of the heat capacity. |
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U71.00163: Improved effective equation for the Rashba spin-orbit coupling in semiconductor nanowires Samuel D. Escribano, Alfredo Levy-Yeyati, Elsa Prada Semiconductor Rashba nanowires are quasi-1D materials that have large spin-orbit (SO) coupling arising from a broken crystal potential symmetry due to an external electric field. There exist parametrized multiband models that can describe accurately this effect. However, simplified single band models are highly desirable to study geometries of recent experimental interes but at a reduced computational cost. Commonly used conduction band approximations, valid for bulk materials, greatly underestimate the SO coupling in Zinc-blende crystal structures and overestimate it for Wurzite ones when applied to finite cross-section wires, where confinement effects turn out to play an important role. We demonstrate [1] that an effective equation for the linear Rashba SO coupling of the semiconductor conduction band can reproduce the behaviour of more sophisticated eight-band k.p model calculations. This is achieved by adjusting a single effective parameter that depends on the nanowire crystal structure and its chemical composition. We further compare our results with the Rashba coupling extracted from magnetoconductance measurements in several experiments on InAs and InSb nanowires, finding excellent agreement. |
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U71.00164: Direct determination of the zero-field splitting for Fe3+ ion in the oxalate mineral stepanovite Tao Xie, Andrey Podlesnyak We employed inelastic neutron scattering (INS), specific heat, and magnetization analysis to study the magnetism in a synthetic sample of a two-dimensional natural metal-organic framework material, stepanovite NaMgFe(C2O4)3(9H2O). No long-range magnetic order can be observed down to 0.5 K. The INS spectra show two dispersionless excitations at energy transfer, 0.03 and 0.05 meV, which are derived from the magnetic transitions between zero-field splitting (ZFS) of S = 5/2 ground state multiplets of Fe3+ ion. Further analysis of the INS results shows that the Fe3+ ion has an easy-axis anisotropy with axial ZFS parameter D = −0.0128(5) meV and rhombic parameter E = 0.0014(5) meV. |
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U71.00165: Time-resolved magneto-optical imaging assisted by deep-learning video frame interpolation Tomosato Hioki, Daiki Kimura, Jayakorn Vongkulbhisal, Subhajit Chaudhury, Michiaki Tatsubori, Eiji Saitoh
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U71.00166: Magnetic fragmentation within an arctic circle Lucas Reneuve In frustrated spin systems, the ground state manifold is often completely defined by local constrains inherited from the frustrated nature of spin interactions. These constraints give rise to exotic phases hosting for instance very peculiar dynamics: magnetic monopoles, loop-like excitations, etc. While these systems have been studied widely under open or periodic boundaries conditions, recent interest has been given to another kind of boundaries in 2D: Domain Wall Boundary Conditions. By fixing the spins on the borders of the system in a controlled way, the collective organisation unexpectedly propagates at long distance within the bulk of the system, which results in a phase separation. This is known as the Arctic Circle Phenomenon [1]. We show in this work that a Monte Carlo approach with the appropriate dynamics highlights this phenomenon in several models that are experimentally accessible with the use of meta magnets, like artificial spin ices [2]. More precisely, we demonstrate that we may observe a fragmented spin liquid [3] within a kagome-based Arctic Circle. |
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U71.00167: Superparamagnetic Fe@Au Core/shell nanoparticles and their feasibility for magnetic hyperthermia Bianca Paola Meneses Brassea, Mohamed F. Sanad, Dawn S. Blazer, Shirin Pourmiri, George C Hadjipanayis, 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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U71.00168: Various challenges in realizing spin-gapless semiconductivity in Ti2CoSi Evan O'Leary, Bishnu Dahal, Parashu Kharel, Pavel Lukashev Spin-gapless semiconductors are recently discovered class of materials that behave as an insulator for one spin channel and as a zero-gap semiconductor for the opposite spin. Here, we show from first-principle calculations that one such material Ti2CoSi predicted to exhibit spin-gapless semiconductivity has an energetically close non-spin-polarized phase. In particular, we show that the regular Heusler phase of this material is non-magnetic, while the inverted Heusler phase is nearly spin-gapless semiconducting, with a very small energy difference of about 0.1 eV per 16-atom cell, in favor of the regular Heusler structure. Moreover, we also show that a 100% spin polarization in inverted Heusler phase is detrimentally affected by the emergence of surface states in thin-film geometry. These results need to be taken into account for realistic implementations of this and similar materials in nano-device applications, which rely on highly spin-polarized current in thin-film geometry. |
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U71.00169: Ni-Cu Nanoparticles and Their Feasibility for Magnetic Hyperthermia Bianca Paola Meneses Brassea, Edgar A. Borrego, Dawn S. Blazer, Mohamed F. Sanad, Shirin Pourmiri, Denisse A. Gutierrez, Armando Varela-Ramirez, George C Hadjipanayis, Ahmed A El-Gendy Ni-Cu nanoparticles (NPs) synthesized by reducting Ni and Cu from metal precursors using a sol–gel route and annealing at 300 °C for 1, 2, 3, 6, 8, and 10 h for controlled self-regulating magnetic hyperthermia (MH) applications. Morphology and crystal structure revealed spherical NPs with cubic structure and average size of 50, 60, 53, 87, and 87 nm for as-made and annealed samples. Ferromagnetic behavior with Ms 13–20 emu/g at 300 K. ZFC-FC curves revealed superparamagnetic Nps with blocking temperature (TB) of 196–260 K. Heating rate 0.1-1.7 °C/min and specific absorption rate (SAR) of 6–80 W/g. Saturation at Curie temperature (Tc) 30–61 °C within the therapeutic temperature limit. In vitro cytotoxicity test of these Ni-Cu samples performed via exposing human breast cancer MDA-MB231 cells to a gradient of concentrations of the sample with 53 nm particles (annealed at 300 °C for 3 h) revealing biocompatibility for future in vitro/in vivo MH treatment of cancer. |
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U71.00170: The conservation of the angular momentum in ultrafast spin dynamics Jacopo Simoni, Stefano Sanvito The total angular momentum of a close system is a conserved quantity, which should remain constant in time for any excitation experiment once the pumping signal has extinguished. Such conservation, however, is never satisfied in practice in any real-time first principles description of the demagnetization process. Furthermore, there is a growing experimental evidence that the same takes place in experiments. The missing angular momentum is usually associated to lattice vibrations, which are not measured experimentally and are never considered in real-time simulations. Here we critically analyse the issue and conclude that current state-of-the-art simulations violate angular momentum conservation already at the electronic level of description. This shortcoming originates from an oversimplified description of the spin-orbit coupling, which includes atomic contributions but neglects completely that of itinerant electrons. We corroborate our findings with time-dependent simulations using model tight-binding Hamiltonians, and show that indeed such conservation can be re-introduced by an appropriate choice of spin-orbit coupling. The consequences of our findings on recent experiments are also discussed. |
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U71.00171: Time-resolved measurements of electronically tunable magnetism in LaAlO3/SrTiO3 Erin Fierro, Kitae Eom, Chang-Beom Eom, Patrick R Irvin, Jeremy Levy Tunable magnetism at the the LaAlO3/SrTiO3 (LAO/STO) has been observed, but its mechanism remains unknown. Previous experimental results, such as an observed Kondo effect[1] and magnetic force microscopy (MFM) measurements[2], confirm electrically-tunable magnetism in LAO/STO at room temperature. While optical probing further characterizes this magnetic behavior as optically controllable[3], studies of the dynamics of this magnetization remain incomplete. To resolve this transition, we take advantage of magneto-optical Kerr effect (MOKE) microscopy. By by pump-and-probe optical measurements, the behavior of the system during transition can be characterized. Understanding this transition as it evolves will reveal the mechanism that controls the property and enrich our understanding of both the interface and this exotic magnetism. |
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U71.00172: Absence of moment fragmentation in the mixed B site pyrochlore oxide Nd2GaSbO7 Benito Gonzalez, Steven Gomez, Paul M. Sarte, Micaela Zelensky, Alannah M. Hallas, Edward Pace, Stuart Calder, Matthew Brandon Stone, Yixi Su, Erxi Feng, Duc Le, Paul Attfield, Stephen D. Wilson, Adam Aczel, Christopher Wiebe Nd-based pyrochlore compounds (Nd2B2O7) are of particular interest in the framework of moment fragmentation physics. Introduction of charge disorder on a non-magnetic B site in these systems is expected to reduce the symmetry about the Nd site, significantly suppressing moment fragmentation. Here we report on a polycrystalline sample of a Nd pyrochlore with a charge-disordered B-site, Nd2GaSbO7. We show that this compound orders into the “all-in, all-out” magnetic structure below TN = 1 K, one of the highest ordering temperatures reported for a Nd pyrochlore. The Ising-like character of the moments and the dipolar-octupolar nature of the ground state doublet are confirmed via bulk property measurements and crystal field analysis, respectively, both of which are necessary for moment fragmentation. Although inelastic neutron scattering results show a flat mode at 0.253(6) meV, the diffuse neutron scattering was not able to resolve any spin-ice correlations. These results may suggest the absence of moment fragmentation in this system. |
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U71.00173: Multiple stable Bloch points in confined helimagnetic nanostructures Martin Lang, Marijan Beg, Hans Fangohr It was predicted by Beg et al. [1] that a stable Bloch point (BP) exists at the interface of two nano-disks with Dzyaloshinskii-Moriya-interaction of opposite chirality in the absence of an external magnetic field. Two different configurations, head-to-head and tail-to-tail, were discovered and switching between them was demonstrated by using an external magnetic field. The two co-existing distinct stable configurations make BPs a possible candidate for future memory devices. Mandatory for any application is finding multiple BPs in a single sample. |
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U71.00174: Low dimensionality and magnetic frustration of Ni5.15Sn0.85(O2BO3)2 hulsite Cynthia Paola Medrano, Daniele C Freitas, Edson C. Pasamani, J. A. L. C. Resende, Mariella Alzamora, Eduardo Granado, Carlos William Galdino, Mucio A. Continentino, Elisa Baggio-Saitovitch, Dalber R Candela Ni5.15Sn0.85(O2BO3)2 hulsite has a complex magnetic transition at 180 K, one of the highest order temperatures among the oxyborates [1]. To characterize the low-dimensional properties of Ni5.15Sn0.85(O2BO3)2 hulsite, we combine bulk techniques as x-ray diffraction, XAS, magnetic and specific heat with local probe 119Sn Mössbauer spectroscopy. Hulsite compounds are the less studied in the family of oxyborates, their properties are determined by planes instead of one-dimensional subunits as ladders in ludwigites or ribbons in warwickites. The transition metal ions in hulsite form two planar substructures, one is a rectangular lattice, responsible for the magnetic transition, the other is a triangular lattice, which does not order down to 3 K. The experimental results suggest a spin-liquid behavior for this subsystem. The two planar substructures coexist as independent magnetic subsystems down to the lowest temperatures of our experiments [1]. |
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U71.00175: Current-Induced Crystallisation in Heusler Alloy Films William Frost, Kelvin Elphick, Marjan Samiepour, Atsufumi Hirohata Half-metallic Heusler alloys have been investigated intensively in a view of spintronic device applications as an ideal spin source. However, a major obstacle for the applications is the requirement of high annealing temperature for their crystallisation. We have recently reported the reduction in the crystallisation temperature by promoting layer-by-layer growth on a (110) surface. In this study, we achieved current-induced crystallisation of a Co2FeAl0.5Si0.5(110) Heusler alloy film by applying controlled current density, leading to the change in the corresponding resistivity. Due to the nature of a simple electrical current introduction, a nanoelectronics device does not require annealing processes but stores the operation cycle permanently, which minimises any atomic diffusion and interfacial mixing to degrade their performance. Hence, such current-induced crystallisation is expected to be used in a variety of nanoelectronics devices, including a neuromorphic node network, which can revolutionalise solid state memory. |
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U71.00176: Spin waves in ferro- and antiferromagnetic noncollinear magnets with Dzyaloshinskii-Moriya interaction Flaviano dos Santos, Manuel dos Santos Dias, Samir Lounis Broken inversion symmetry combined with the spin-orbit interaction generates a finite Dzyaloshinskii-Moriya interaction (DMI), which can induce noncollinear spin textures of chiral nature. In a ferromagnet, the DMI also causes the spin waves to be nonreciprocal, i.e., spin waves propagating with opposite wave vectors are characterized by different group velocities, energies, and lifetimes. We address the case of complex spin textures, such as ferro- and antiferromagnetic spin-spiral and skyrmion systems, where the manifestation of DMI-induced chiral asymmetries remains unexplored. We discuss such nonreciprocal effects and propose ways of accessing the magnitude and direction of the DMI vectors in the context of spin-polarized or spin-resolved inelastic scattering experiments. In particular, we show that even zero-net-magnetization systems, such as collinear antiferromagnets and cycloidal spin spirals, can have spin-wave modes that are individually nonreciprocal while the total spin-wave spectrum remains reciprocal. |
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U71.00177: Mapping out the electronic and magnetic transitions in mixed-valent La1-xSrxMnO3 thin films James Alan Payne, Dakota Brown, Thomas Pekarek, Maitri P 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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U71.00178: Demonstration of Spin Current Switch across Ferro-Antiferromagnetic Transition Yi-Hui Zhang, Ting-Wei Weng, Tsao-Chi Chuang, Danru Qu, Ssu Yen Huang FeRh has been attracted great attention due to its first-order magnetic phase transition between antiferromagnetic (AFM) and ferromagnetic (FM) states around room temperature. Moreover, the phase-transition temperature can be readily modulated by the magnetic field. In our work, we demonstrate a spin current switch through the phase transition in FeRh by utilizing electrical or thermal excitation [1]. While a large magnetoresistance ratio of 50% is obtained between the AFM and FM states, the spin current valve’s on/off ratio can be virtually infinite in the thermal transport. The on/off valve, triggered by modulating the temperature or magnetic field, shows a promising feature for the AFM spin current switching devices. |
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U71.00179: Probing the spin-glass freezing transition by spin current PO-HSUN WU, Yen-Chang Tu, Danru Qu, Hsia-Ling Liang, Shang-Fan Lee, Ssu Yen Huang Recently, the enhanced pure spin current through spin fluctuations in antiferromagnetic (AF) insulators during the magnetic phase transition has attracted great attention. We report the spin current enhancement in the short-range magnetic ordered spin glass (SG) Cu1−xMnx alloys in this work [1]. We used the thermally driven spin current from YIG to investigate the spin frustrations and spin fluctuations in Cu1−xMnx alloys with various compositions, which results in a transition of the alloys from the SG state to the AF state. We show that the strongest spin fluctuation occurs at a temperature considerably higher than the magnetic critical temperature. Consequently, the thermally driven spin current can probe the spin susceptibility and the complex spin-freezing process. Furthermore, we point out the importance of the effective number of valence electrons in tailoring the spin Hall angle, which specifies the charge-to-spin conversion efficiency, in Cu1−xMnx alloys. |
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U71.00180: Tunable Magnetic Anisotropy and Curie Temperature in Cr1+δTe2 Thin Films Yuita Fujisawa, Markel Pardo Almanza, Jennifer Garland, Yoshinori Okada Two-dimensional (2D) magnetic materials have recently attracted interest for potential use in spintronic applications. The magnetic transition metal dichalcogenide (TMD) Cr1+δTe2 is a promising candidate to host novel magnetic phases, but systematic control of the anisotropy and thermal stability remains a challenge. In this work, we demonstrate tunable magnetic anisotropy and Curie temperature (TC) in epitaxial Cr1+δTe2 films grown by molecular beam epitaxy (MBE). Post-deposition annealing temperature is used to smoothly alter δ, the fraction of Cr atoms self-intercalated between neighboring CrTe2 layers. Increasing δ results in monotonic enhancement of TC from 160 to 350 K and the rotation of magnetic anisotropy from out-of-plane to in-plane easy-axis configuration for fixed film thickness. This novel control of magnetism opens up pathways for realizing future spintronic devices. |
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U71.00181: Influence of nonuniform magnetization reorientation on spin-orbit torque measurements Ryan Greening, Xin Fan Measurement of spin-orbit torque in a ferromagnetic/nonmagnetic multilayer is typically based on the assumption that the entire ferromagnetic layer uniformly responds to the spin-orbit torque. This assumption breaks down when the thickness of the ferromagnetic layer is comparable to the exchange length, which is only a few nanometers for typical 3d transition ferromagnets. The nonuniform magnetization reorientation coupled with a nonuniform contribution of each magnetic sublayer to the magnetoresistance or the Kerr effect may impact the accuracy in the extrapolation of spin-orbit torque. In this presentation, we use a numerical model to investigate the impact nonuniform magnetization tilting has on spin-orbit torque measurements using three different experimental techniques: the second-harmonic method, the spin torque ferromagnetic resonance method, and the magneto-optic-Kerr-effect method. |
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U71.00182: Electron spin resonance of defects in the organic spin chains compounds (o-DMTTF)2X Loïc Soriano, Sylvain Bertaina, julian zeisner, Vladislav kataev, Marc Fourmigué, Hervé Vezin, Maylis Orio Defects in spin chains were a subject of great interest over the last decades.The spin-Peierls systems like the organic spin chains compounds (o-DMTTF)2X (X = Cl,Br,I) have an S = 0 ground state. However it is known [1] that a break in the translational symmetry induces S = 1/2 ground state made by hundreds of spins of the chain. A low temperature paramagnetic signal is often observed and commonly attributed to extrinsic impurities. |
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U71.00183: Investigation of structural and physical properties of trilayer nickelates - R4Ni3O10 (R = La, Pr and Nd). Dibyata Rout, Sanchayeta Ranajit Mudi, Marco Hoffmann, Sven Spachmann, Rudiger Klingeler, Surjeet Singh The Ruddlesden Popper nickelates with the general formula Rn+1NinO3n+1 (n = 1,2,3 and ∞) have seen a resurgence of interest due to the recent discovery of superconductivity in Nd0.8Sr0.2NiO2 thin films1. Moreover, ARPES studies on the n = 3 member(La4Ni3O10) has revealed a large hole Fermi surface that closely resembles that of optimally hole doped cuprates2. These nickelates, being structurally and electronically analogous to the HTSCs, provide an excellent platform to investigate the origin of superconductivity in HTSCs. Here we show the detailed investigation of the structure-property relationship in the trilayer nickelates - R4Ni3O10 (R = La, Pr and Nd) across the metal-to-metal transition3 observed at TMMT =135 K (La), 156 K(Pr) and 160 K(Nd). Distinct anomaly in the lattice parameters, magnetic susceptibility, transport and thermal expansion is seen at MMT, suggesting strong coupling between magnetic,electronic and structural degrees of freedom. The magnetic long range ordering in both R = Pr and Nd is highly suppressed despite a large value of θP, indicating the presence of strong frustration. |
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U71.00184: Dynamic structure factor of a spin chain with three-spin interactions in a transverse magnetic field Oz Bonfim, J. Florencio We investigate the spin dynamics of a quantum spin chain with three-spin interactions in a transverse magnetic field. The longitudinal dynamic structure factor is calculated in function of temperature and applied transverse magnetic fields. Calculations are performed with chains up to 14 spins with periodic boundary conditions. Both direct diagonalization and the method of recurrent relations are used. Although the calculations are done with finite chains the results can be extrapolated to the thermodynamic limit. The frequency dependence of the longitudinal dynamic structure factor at several values of temperature, magnetic field, and wave vector, is calculated and its behavior analyzed. |
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U71.00185: Classical mechanism for the anomalous enhancement of Hall resistivity during magnetization reversal Christopher Ard, Olivier Pinaud, Hua Chen Abstract: 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 perturbing the classical conductivity tensor randomly while modeling the hysteresis loop, we were able to show that an anomalous enhancement of the Hall resistivity can arise before the ferromagnet is fully switched by a perpendicular magnetic field. |
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U71.00186: Chiral Magnetic Texture and Spin Dynamics in Magnetic Superlattices Luis Flacke, Valentin Ahrens, Simon Mendisch, Lukas Körber, Attila Kákay, Elisabeth Meidinger, Misbah Yaqoob, Markus Becherer, Lukas Liensberger, Matthias Althammer, Hans Huebl, Stephan Geprägs, Rudolf Gross, Mathias Weiler Chiral magnetic textures, in particular magnetic skyrmions, are attractive for data storage and processing via magnetic “racetracks” and logic gates. These textures may also be used as neurotransmitters in artificial neural networks for non-conventional computing. For such applications, thin-film, all-metallic magnetic heterostructures with chiral texture stabilized by interfacial Dzyaloshinskii-Moriya interaction (iDMI) are ideal candidates. |
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U71.00187: Interaction contributions to the spin Hall effect in the Kane-Mele-Hubbard model Siheng Wang, Christopher Ard, Hua Chen Different from the charge Hall effect in which Coulomb interaction is necessary for establishing steady states, the spin Hall effect (SHE) has usually been understood as a non-interacting effect, where the steady-state is reached by spin-orbit-coupling-induced intrinsic or extrinsic spin relaxation. However, in nonmagnetic systems proximate to a magnetic instability, interaction may play a significant role in the SHE. Here we study the interaction contributions to the SHE by using the nonequilibrium Green function approach in a concrete model: the Kane-Mele-Hubbard model. The model involves nearest-neighbor spin-independent hopping and 2nd nearest-neighbor spin-dependent hopping of s electrons on a honeycomb lattice. The on-site Hubbard interaction is treated by an unrestricted Hartree-Fock decoupling self-consistently. By solving the non-equilibrium Green function of a finite system coupled to two leads, we calculate the spin accumulation on the lateral edges which is a direct experimental observable. We compare the cases with and without the Hubbard interaction, and study the connection between the SHE and local spin susceptibility at the edges. |
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U71.00188: Effects of Coupling between Single Molecular Magnet (SMM) and Ferromagnetic Electrode on Magnetic Tunnel Junction-Based Molecular Spintronic Devices Marzieh Savadkoohi, Bishnu Dahal, Andrew Grizzle, Christopher D’Angelo, Pawan Tyagi Magnetic Tunnel Junction-based Molecular spintronic devices (MTJMSDs) approach allows covalent bonding of Single Molecular Magnet (SMM) between two ferromagnetic electrodes (FMEs) of a MTJ along the exposed sides.This research studies variation of magnetic coupling between the SMM and two FMEs.We conducted Monte Carlo Simulations (MCS) by defining MTJMSD in an Ising model framework.We varied the SMM-FMEs Heisenberg exchange coupling nature and strengths to simulate a wide range of device configurations.In this study we investigated SMM forming (i)FM coupling with two FMEs (ii)anti-FM couplings and (iii) FM coupling with one FME and anti-FM coupling with another one.The SMM-FME coupling variation effect was studied on the magnetic moment, heat capacity, and magnetic susceptibility of the two FME and overall MTJMSD.We also studied the spatial and temporal behavior of MTJMSD as a function of SMM couplings.Our MCS study agrees with the experimental observations of time dependent changes on MTJMSD magnetic and transport properties.Ferromagnetic SMM-FMEs coupling resulted in maximum magnetization while antiparallel couplings led to magnetic moment close to zero.This study provides explanation for the experimentally observed current suppression phenomenon on MTJMSD at room temperature. |
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U71.00189: Effect of passivation layers on the magnetic properties of SmCo5 Peter Sharma, Ana Lima Sharma, David Lidsky, Michael P Siegal, Tzu-Ming Lu
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U71.00190: Characterizing Single Molecular Spin State Effects on Magnetic Tunnel Junction-Based Molecular Spintronics Devices Using Monte Carlo Simulations Andrew Grizzle, Bishnu Dahal, Marzieh Savadkoohi, Christopher D'Angelo, Pawan Tyagi Magnetic tunnel junction molecular spintronics devices (MTJMSDs) are metamaterials realized by simultaneously connecting Single Molecular Magnets (SMM) between two ferromagnetic (FM) electrodes of an optimized magnetic tunnel junction (MTJ)1. SMM-FM interactions produce novel optical, electronic, and magnetic properties. SMMs exhibit a wide range of spin states (Sm), which is experimentally challenging to quantify. Here, we report Monte Carlo Simulations (MCS) exploring SMM's Sm impact on the MTJMSD equilibrium state. This study used 3D Ising model of MTJMSD to conduct MCS. Following a Markov process, the device's temporal and spatial magnetic moments were analyzed as a function of Sm (0-4) and thermal energy (0.01-0.5). We found that anti-FM coupling occurred when a paramagnetic SMM made anti-FM and FM coupling to the first and the second FM electrodes, respectively. Moreover, we found that the SMM spin state's magnitude must be above 0.2 to create a significant impact on the MTJMSD's magnetic properties. Our MCS also showed that SMM's spin impacted the spatial correlation length scale. We also studied impact of SMM's spin state on the heat capacity and magnetic susceptibility properties of MTJMSDs. |
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U71.00191: Magnetic Properties and Losses of Iron/Cobalt-Based Ferrofluids
Kent Hess, W. Korzi, L. Krushinski, K. Langford, O. Thomas, M. Devadas, E. Hondrogiannis, V. Smolyaninova kent hess, Lynn Krushinski, Ellen M Hondrogiannis, Mary S Devadas, Will Korzi, Vera N Smolyaninova, Kameron Langford, O Thomas Ferrofluids have fascinating properties not only for basic research, but also because of |
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U71.00192: Monte Carlo Simulations Investigating the Effect of Intra-Molecular Coupling on the Magnetic Properties of Magnetic Tunnel Junction Based Molecular Spintronics Devices Pius Suh, Marzieh Savadkoohi, Andrew Grizzle, Bishnu Dahal, Christopher D’Angelo, Pawan Tyagi Paramagnetic molecules, with a net spin state, can tailor magnetic exchange coupling between two ferromagnetic (FM) electrodes in magnetic tunnel junction based molecular spintronics devices (MTJMSD). Magnetic coupling between paramagnetic molecules and two FM electrodes in MTJ-based devices is dependent on a net molecular spin state. However, there is a knowledge gap about the role of the intramolecular coupling on the magnetic properties of the MTJMSD. This research tested the hypothesis that variation in the strength and nature of intra-molecular coupling among multiple segments of a molecule can produce a new testbed to observe the novel phenomenon. Here, we investigated the effect of intramolecular coupling (Jm) on the MTJMSD magnetic properties using Monte Carlo Simulation (MCS). We varied Jm strength and studied its subsequent impact on the MTJMSD magnetic properties at different thermal energies. Device magnetization was recorded as a function of time for various simulation counts to achieve device stabilization and to capture temporal evolution. Our MCS results showed that low Jm yielded an impact localized around the junction area. This behavior creates a platform for more studies on the effect of intra-molecular coupling on the magnetic properties of the MTJMSD. |
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U71.00193: Chemical stability of magnetocaloric La(FexCoySi1-x-y)13 particles Vaibhav Sharma, khushar Javed, Anis Biswas, Shalabh Gupta, Radhika Barua, Vitalji Pecharsky, Magundappa Hadimani Magnetocaloric refrigeration is an emerging technology that shows the potential to replace traditional vapor-compression systems. Considering water is a common heat exchange fluid in magnetocaloric devices, this study focuses on the stability of the room temperature magnetocaloric effect in La(FexCoySi1-x-y)13 alloys. Material characterization was performed on both milled and ground La(Fe0.84Co0.07Si0.08)13 powders stored in water and air for up to 14 days. Experimental results show that the powders grounded after storing in water, and air retain sharp magnetovolume transitions with entropy change (ΔS) values of 10.3 J/Kg.K and 7.1 J/Kg.K respectively (μH= 3 T), while the milled powders exhibit low ΔS values. The milled powders stored in air show slightly broadened transitions, whereas those stored in water show significantly broadened transitions with enhanced magnetization that can be attributed to the ferrimagnetic Fe3O4. Overall, our results indicate that ground La(FexCoySi(1-x-y))13 powders show promising MCE effects after exposure to air and water, while properties of milled powder deteriorate rapidly. |
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U71.00194: Non-classical spin transfer effects in an antiferromagnet Alexander Mitrofanov, Sergei Urazhdin Studies of spin transfer (ST) effects enabling electronic control of the Neel order in antiferromagnet-based (AF) spintronic devices have so far focused on the mechanisms that can be understood within semiclassical approximation for magnetism. However, the ground state of AFs is not a N’eel state, but rather an entangled spin state involving large quantum magnetization fluctuations, which may be expected to result in ST effects not captured by the semi-classical approximation. We utilize tight-binding simulations in a 1D AF modeled as a chain of quantum Heisenberg spins. Among the effects elucidated by the simulations are efficient excitation of multiple fractionalized magnetic excitation (spinon) quanta by a single electron, which is not possible in ferromagnets due to angular momentum conservation, as well as quantum interference of spin wavefunctions, making it possible to induce magnetization dynamics with amplitudes exceeding the transferred magnetic moment. Our results suggest the possibility to utilize non-classical contributions to ST to achieve efficient spin conversion and electronic control of static and dynamical states in AFs. |
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U71.00195: The Effect of Single Molecular Magnet Positions Between Ferromagnetic Electrodes of Variable Thickness on the Magnetic Properties of the Molecular Spintronics Devices. Uzma Amir, Andrew Grizzle, Bishnu Dahal, Christopher D’Angelo, Vincent Lamberti, Marzieh Savadkoohi, Pawan Tyagi The magnetic tunnel junction (MTJ) based molecular spintronics device (MTJMSD) approach offers myriad opportunities to investigate various combinations of magnetic molecules and ferromagnetic (FM) electrodes to realize novel forms of magnetic metamaterials. MTJMSD is formed by placing magnetic molecular channels along the exposed sides of a MTJ, and hence molecules appear in the form of a ring around the tunnel barrier. However, there is a knowledge gap about the role of the thickness of the FM electrodes on the magnetic properties of the MTJMSD. This paper provides insights about effect of placing the molecular layer between two FM electrodes of different thicknesses while varying exchange coupling between molecules and the FMs at different thermal energy. We have studied the effect of FM electrode thickness using continuous spin Monte Carlo Simulation (MSC). The effect of FM electrode thickness was strongly dependent of the molecule coupling with the two FM electrodes. Thinner FM electrodes achieved the equilibrium state quicker as compared to thicker FM. The spatial correlation of the magnetic molecular spin with FM electrodes spins was dependent on the FM electrode thickness. Thermal energy impacted the molecular coupling influence on the FM electrode of different thickness. |
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U71.00196: Charge-spin conversion effects in topological semimetal Bing Zhao, Saroj Dash An outstanding feature of topological quantum materials is their unique spin topology in the electronic band structures with an expected novel charge to spin conversion effects. In the Weyl semimetal candidate WTe2, we observed both conventional (1) and unconventional (2) charge to spin conversion effects at room temperature. In addition to the conventional spin Hall and Rashba Edelstein effects, we also measured an unconventional charge to spin conversion component in WTe2. Such a large spin polarization can be possible in WTe2 due to a reduced crystal symmetry combined with its large spin Berry curvature, spin orbit interaction with a novel spin texture of the Fermi states (2). These findings provide an efficient route for generating spin polarization in low symmetry topological materials and their heterostructures. |
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U71.00197: Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene Bogdan Karpiak, Saroj Dash Engineering 2D material heterostructures by combining the best of different materials in one ultimate unit can offer a plethora of opportunities in condensed matter physics. Here, in the van der Waals heterostructures of the ferromagnetic insulator Cr2Ge2Te6 and graphene, our observations indicate an out-of-plane proximity-induced ferromagnetic exchange interaction in graphene. The perpendicular magnetic anisotropy of Cr2Ge2Te6 results in significant modification of the spin transport and precession in graphene, which can be ascribed to the proximity-induced exchange interaction. Our results open up opportunities for the realization of proximity-induced magnetic interactions and spin filters in 2D material heterostructures and can form the basic building blocks for future spintronic and topological quantum devices. |
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U71.00198: Nonlinear Optical Imaging of Current Induced Spin Switching of Antiferromagnetic NiO: Spin Torque or Magnetoelasticity? Joongwon Lee, Yongjian Tang, Antonio B Mei, Darrell Schlom, Daniel C Ralph, Farhan Rana Electrical switching of the Neel order in antiferromagnetic (AF) materials via spin orbit torque (SOT) has drawn considerable interest [1]. Recent reports have suggested that magnetoelastic (ME) effects could be responsible for the measured spin Hall magnetoresistance (SHMR) changes that are used to detect switching [2]. Table-top techniques that can directly image all magnetic domains in AF materials are needed to better understand the physics associated with spin switching. We show that optical second harmonic generation (SHG) can be used to image and identify all spin and twin domains in thin AF NiO. Using this technique, we image spin domains, and their current-induced switching, in epitaxially-grown NiO/Pt devices. Our results show that AF switching is spatially non-uniform. We observe different regions that individually exhibit AF switching in agreement with SOT or ME predictions. We also observe regions that do not exhibit any switching. We also demonstrate that SHMR changes can be induced by optically heating the devices in patterns similar to Joule heating induced by an applied current thereby demonstrating the importance of ME effects. [1] Phys. Rev. Lett. 120, 207204 (2018). [2] Phys. Rev. Lett. 123, 227203 (2019). |
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U71.00199: Study of the Spin Glass Transition Using Coherent Magnetic X-ray Scattering Sudip Pandey, Jing-Jin Song, Sheena Kusum Kishor Patel, Rupak Bhattacharya, Yi Yang, M. Brian Maple, Eric Fullerton, Claudio Mazzoli, Sujoy Roy, Chandra M Varma, Sunil K Sinha Spin Glass represents a new state of matter which has been intensely studied experimentally and theoretically since the 1970’s. The principal methods to study the spin-glass transition, besides some elaborate and elegant theoretical constructions, have been numerical computer simulations and neutron spin echo measurements. However, the existence of a true second-order phase transition from the paramagnetic to the spin glass state accompanied by critical fluctuations has been difficult to establish experimentally with neutron scattering owing to the long-time scales involved. We show that the dynamical correlations of the spin-glass transition are embedded in measurements of the four-spin correlations at very long times. This information is directly available in the temporal correlations of the intensity, which encode the spin-orientation memory, obtained by the technique of resonant magnetic x-ray photon correlation spectroscopy. We have implemented this method to observe and accurately characterize the critical slowing down of the spin orientation fluctuations in the classic metallic spin glass alloy Cu(Mn) over time scales of 1 to 10 secs. |
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U71.00200: Competing Effects of Inter-Ferromagnetic Electrode Coupling and Paramagnetic Molecule Induced Exchange Coupling in Magnetic Tunnel Junction-Based Molecular Spintronics Devices Hayden Brown, Andrew Grizzle, Christopher D'Angelo, Bishnu Dahal, Vincent Lamberti, Marzieh Savadkoohi, Pawan Tyagi In magnetic tunnel junction based molecular spintronics device (MTJMSD), two ferromagnetic electrodes (FMEs) are connected by an insulator film, and molecular channels along the exposed sides of the FMEs. Here, we report a Monte Carlo simulation (MCS) study showing the impact of inter-FME coupling via the insulator on the MTJMSD’s magnetic properties. We varied the direct inter-FMEs coupling strength and nature (i.e., JLR) for different molecule-induced exchange coupling types. Antiferromagnetic JLR enhanced the effect of molecule induced antiferromagnetic coupling effect. Whereas ferromagnetic JLR directly competed with the opposite nature of molecule induced antiferromagnetic molecular coupling. We observed that positive JLR with a magnitude of ≈ 0.2 reversed the five times stronger molecule induced antiferromagnetic coupling. When JLR = 0, the device was able to assume both antiferromagnetic and ferromagnetic states solely based on the molecular coupling effect. MCS studies showed that when JLR increased beyond a critical level, the paramagnetic molecules' spin orientations transitioned to a highly disordered state. In the disordered state, the paramagnetic molecules did not produce any long-range effect on MTJMSD. |
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U71.00201: The magneto-thermal properties of Ni-deficient Mn0.5+xFe0.5Ni1-xSi0.95Al0.05 intermetallic System Ranjit Chandra Das, Arjun Pathak, Prayushi Bhorania, Mahmud Khan The thermal response of a magnetic material to an external magnetic field is often described as the magnetocaloric effect (MCE). The magnetic entropy change of a material is one of the parameters that quantifies MCE. The intermetallic compound Mn0.5Fe0.5NiSi0.95Al0.05 exhibits a first order magnetostructural phase transition near 315 K. In the vicinity of the phase transition, a large magnetic entropy change of -15 J/kg K for a field change of 20 kOe is observed. This property along with the fact that the material consist of inexpensive, nontoxic, and non-rare earth elements, is considered a viable candidate for use in the magnetic refrigeration technology. A major issue that need to be solved in this material is a large thermal hysteresis that accompanies the first order phase transition. Therefore, it is interesting to explore possible ways to suppress the thermal hysteresis in Mn0.5Fe0.5NiSi0.95Al0.05 and related compounds. Here, we will present an experimental study on the effects of substituting Mn with Ni on the magnetic and magnetocaloric properties of a series of Mn0.5+xFe0.5Ni1-xSi0.95Al0.05 intermetallic compounds. A detailed discussion on the structural, magnetic and magnetocaloric properties of the materials will be presented. |
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U71.00202: Antiferromagnetic coupling in the epitaxial growth of Fe on the CrN (001) surface Rodrigo Ponce Perez, Khan Alam, Noboru Takeuchi, Arthur Smith By spin-polarized DFT calculations we investigated the structural, electronic and magnetic properties of the epitaxial growth of Fe on the CrN (001) surface. We employed the Surface Formation Energy (SFE) formalism to investigated the thermodynamic stability of the different surface. According with the calculations four structures results to be stables: The ideal CrN surface terminated and three different surfaces with Fe (The A12-Fe, A-3Fe and A-CrN models). The magnetic properties of the most stable models are investigated, the ideal CrN surface terminated shows an antiferromagnetic (AFM) behavior with metallic characteristics. In all cases we found a ferromagnetic (FM) behavior in the zones with contains only Fe atoms. About the interaction between the Fe and Cr atoms, an antiferromagnetic coupling is observed in all cases. The average magnetization of the Fe atoms on top of the structure is 2.49 µB, while the average magnetization of the Cr atoms is of the order of 2.5 µB. |
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U71.00203: Anisotropic heat conduction in the spin-spiral state of the cubic helimagnet ZnCr2Se4 Joshua L Cohn, Artem Akopyan, Dharmendra Shukla, Narayan Prasai, Dmytro S. Inosov, Yevhen Onykiienko, Yuliia Tymoshenko, Mathias Doerr, Sergei Zherlitsyn, David J Voneshen, Martin Boehm, Vladimir Tsurkan, Viorel Felea, Alois Loidl The complex magnetic phase diagrama of ZnCr2Se4 includes a quantum critical pointb separating spin-spiral (1.5 ≤ B ≤ 6.5 T) and field-polarized (B > 6.5 T) phases. We present thermal conductivity measurements at T ≤ TN = 21 K in the spin-spiral phase which exhibit anisotropy at T < 2 K, for heat flow along and transverse to the spin-helix propagation direction, that is nonmonotonic in field. Calculated lattice and magnon thermal conductivities that employ a three-dimensional magnon dispersion inferred from neutron scattering studiesc,d favor a magnonic interpretation of the data. |
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U71.00204: Pressure-induced decoupling of the magnetostructural phase transition in MnNiSi-Fe2Ge alloys Vaibhav Sharma, Dustin Clifford, Deepak Kamble, Raju V. Ramanujan, Radhika Barua Polycrystalline (MnNiSi)1-x(Fe2Ge)x (0.33<x<0.35) alloys were prepared by the arc-melting technique, and influence of pressure of the magnetostructural response was investigated. All samples demonstrated a coupled first-order magnetostructural transition from a low temperature ferromagnetic (FM)TiNiSi-type orthorhombic phase to a high temperature paramagnetic (PM) Ni2In-type hexagonal phase. The magnetostructural transition temperatures (Tt) was tuned from 365 K– 200 K via chemical pressure employed by varying x in the range of 0.33–0.36. In the x=0.33 sample, hydrostatic pressure shifts Tt to lower temperatures at a rate of ~75 K/GPa, with the coupled nature of magnetostructural transition unchanged. In the x=0.34, 0.35, and 0.36 samples, application of pressures exceeding ~7.5 kbar, results in decoupling of the magnetic transition (FM-PM) and structural transition (orthogonal-hexagonal). The coupling mechanism underlying the magnetostructural response of the (MnNiSi)(1-x) (Fe2Ge)(x) system will be discussed in the context of temperature- and pressure-dependent changes in the crystal structure. Overall, these features emphasize strong coupling between the magnetic spins and the lattice in MnNiSi-based alloys. |
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U71.00205: Calculated Magnetic Properties of Metal-doped Boron Carbon Carbon Nitrogen Nanoribbon Jeffrey Rufinus In the past years, a new type of graphene-based one-dimensional material nanoribbon has been of interest due to the theoretical predictions that this type of material shows a half-metallic property. We present the results of computational studies of (Mn, Cr)-doped Boron Carbon Carbon Nitrogen nanoribbons, the objective of which is to determine whether the presence of these dopants will give rise to ferrimagnetism. We have found that the density and the atomic distance among the dopants affect the magnetic ordering of this type of material. These results provide a meaningful theoretical prediction of metal-doped nanoribbon as a basic candidate of spin electronic devices. |
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U71.00206: Impact of Non-Idealities on Computational Networks built from Low Energy-Barrier Magnet based Stochastic Neurons Samiran Ganguly, Md Golam Morshed, Avik Ghosh Emerging nano-materials technology, in particular low-energy barrier magnet based devices, promises to enable large scale energy-efficient neuromorphic and probabilistic computing hardware for “modern” applications such as optimization, machine learning, Bayesian decision networks, and noisy intermediate scale quantum (NISQ) devices. Simulation based analyses and initial hardware demonstrations have been highly encouraging. Therefore it is prudent to understand the impact of non-idealities that inevitably plague such nascent technologies. We focus the impact of non-idealities of such low-barrier magnets on circuit operations in terms of accuracy and reliability with energy-delay tradeoffs. It is hoped that this analysis helps in understanding the challenges ahead and help develop novel mitigation strategies. |
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U71.00207: Suppression of the ferromagnetic transition due to Y substitution in La2/3Sr1/3MnO3 thin films and Superlattices* Thomas Pekarek, Will Ruiz, Caitlin Kengle, James Alan Payne, Dakota Brown, Maitri P 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 of the key magnetic features 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 we observe 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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U71.00208: The Influence of Grey and White Matter Volume on the Induced Electric Field of the Quadruple Butterfly Coil for Transcranial Magnetic Stimulation Joseph Boldrey, Oluwaponmile Afuwape, Priyam Rastogi, Sarah A Bentil, David C Jiles
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U71.00209: CLIMATE PHYSICS
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U71.00210: Effect Of Spatially Correlated Disorder On Vegetation Pattern Formation In Arid Drylands. Vibhuti Bhushan Jha, Sanid Chirakkal The dynamics of pattern formation in arid drylands can be explained by scale dependent feedback models. |
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U71.00211: Atmospheric Conditions of several Storms in Richmond, VA, from 2018 to 2020 Francis Mensah, Christopher Thompson, Ianthe Pratt In this basic research, we observe velocities, temperatures, relative humidity, visibility and precipitations distributions for several storms, from 2018 to 2020 in Richmond, VA. Data was collected from both Virginia Union University (VUU) and Richmond International Airport (RIA) weather stations. We hypothesize that a storm will be more severe at RIA compared to VUU due to the landscape of each area. Analyses were made and conclusions were drawn. Satellite data was also used to further clarify analyses. |
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U71.00212: GENERAL PHYSICS
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U71.00213: Wave centric interpretation of quantum mechanics Peter Ceperley
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U71.00214: Calculating the CMB Temperature C Hood
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U71.00215: Can Frozen Hydrogen Snowballs Account for Galactic Dark Matter? Alan Kadin It is believed that perhaps 80% of the total mass in most galaxies is distributed in a halo that is larger than the galaxy itself, but is not associated with stars or other known physical objects. Most candidates for dark matter are novel fundamental particles, rather than ordinary atoms. It is suggested here that a more prosaic explanation should be reconsidered: that dark matter in these very cold extragalactic halos consists mostly of frozen hydrogen and trapped helium, in the form of comet-like giant snowballs. If their temperature is close to that of the cosmic black-body radiation (2.7 K), these hydrogen snowballs should be stable for long periods of time, and may be replenished by collisions. Similar suggestions were made decades ago [1], but not serious considered by the astrophysics community. Possible methods to detect these objects indirectly are discussed. |
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U71.00216: Teleportation Systems Towards a Quantum Internet Maria Spiropulu Quantum teleportation is essential for many quantum information technologies including long-distance quantum networks. Using fiber-coupled devices, including state-of-the-art low-noise superconducting nanowire single photon detectors and off-the-shelf optics, we achieve quantum teleportation of time-bin qubits at the telecommunication wavelength of 1536.5 nm. We measure teleportation fidelities of >=90% that are consistent with an analytical model of our system, which includes realistic imperfections. To demonstrate the compatibility of our setup with deployed quantum networks, we teleport qubits over 22 km of single-mode fiber while transmitting qubits over an additional 22 km of fiber. Our systems, which are compatible with emerging solid-state quantum devices, provide a realistic foundation for a high-fidelity quantum internet with practical devices. |
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U71.00217: Forty-one types of physical quantities in arbitrary dimensions Venkatraman Gopalan It is shown that there are 41 types of multivectors representing physical quantities in non-relativistic physics in arbitrary dimensions within the formalism of Clifford Algebra. The classification is based on the action of three symmetry operations on a general multivector: spatial inversion, time-reversal, and a third that is introduced here, namely, wedge reversion. It is shown that the traits of “axiality” and “chirality” are not good basis for extending the classification of multivectors into arbitrary dimensions, and that introducing wedge reversion would allow for such a classification. Since physical properties are typically expressed as tensors, and tensors can be expressed as multivectors, this classification also indirectly classifies tensors. Examples of these multivector types from non-relativistic physics are presented. |
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U71.00218: Performance analysis of a refrigeration engine based on Coulomb coupled systems Anamika Barman, Shailendra Kumar Varshney, Gourab Dutta, Aniket Singha We investigate a cryogenic non-local refrigeration set-up based on Coulomb coupled systems, that circumvents the demand for asymmetric system-to-reservoir coupling, demanded by the recently proposed non-local refrigerators. Investigating the performance and operating regime using quantum-master-equation (QME) approach, we point out that the maximum cooling power for the proposed set-up is limited to about 70% of the optimal design. In addition, we point out that to achieve a target reservoir temperature, lower compared to the average temperature of the current path, the applied voltage must be greater than a given threshold voltage, which is dependent on the reservoir temperature. Proceeding further, we demonstrate that the maximum cooling power, as well as the coefficient of performance deteriorates as one approaches a lower target reservoir temperature. The novelty of the set-up discussed here is the integration of fabrication simplicity along with descent cooling power and may pave the way towards the realization of efficient non-local cryogenic refrigeration systems. |
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U71.00219: Using Dean Flow in a spiral-shaped microfluidic circuit for particle sorting Andreas Mourelatos Microfluidics is the use of small nanoliter channels in order to run experiments quickly and affordably, as compared to other methods. The goal is sorting particles by size using Dean flow in a spiral-shaped microfluidic device. Dean flow is an inertial effect brought about by fluid flow in curved channels, focusing particles into streams by size. Dean flow is achieved by keeping the Reynolds number of the flow low. The most efficient device for a given set of particle sizes is maximized by adjusting the dimensions of a given microfluidic circuit, such as width of channels and curvature of the spiral. |
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U71.00220: Atmosphere DeCarbonIZATION(A-D) Proprietary ReDox-ReactionS’(RRS) Between CO2/CH4
and Earth’s-Crust Dominant RockS’/MineralS(FeldsparS) Yields Useful/Valuable SiC Edward Carl-Ludwig Siegel Atmosphere DeCarbonIZATION (CO2/CH4) via proprietary RRS Carnot-cycleS(CCS) between CO2/CH4 and earth’s-crust(ECDRMS) orthoclase/microcline(KAlSi3O8)-plagioclase-feldsparS:albite (NaAlSi3O8)-binary-join-anorthite(CaAl2Si3O8)igneous/metamorphic mineralS/rockS (graniteS/gneiseS)/sedimentary clayS(kaolin/illite) yielding useful/valuable SiC/“CarBOrundum” VS. CO2-ONLY flora-transpiration but leaving worse CH4 for global warming mitigation/reversal! VS. H2-fuel-cells(HFCS)[Ford/GM/Nikola/Tesla/…any/all!!!] emission of even worse greenhouse-gas steam/H2O-vapor/gas dooming HFCS to limited quantity/mobility-length/mobility-density/…because of severe deleterious effect H2O-vapor deleterious greenhouse-gas effect VS. H2O-vapor capture/condensation (sorely needed in world-wide droughts) eventually increasing auto/weightS/masseS to retard auto-mobility/velocity/acceleration/trip-length/range/time/temporal-duration aka Hindenburg-effect(H-E). |
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U71.00221: Siegel G…P FIRST “Google” Search-Engine and Siegel(AI) Big Data(BD)/Machine-Learning(ML)-FREE Newcomb/Bose-Einstein Condensation(N/BEC)-“Machine” Acceleration Edward Carl-Ludwig Siegel Siegel[U.M./MSU/Okemos(69/70)] FIRST Page-plagiarized “Google” search-engine via “noise-induced phase-transitions”(NITS) power-spectrum(PS) variationS{VS. mere stochastic-resonance(SR)}deriving from Matsubara-Siegel[J.Non-Xline Solids 40,453(80);Ferroelectrics (81);Applied-SC(92)] G…P, Belew[Finding Out About(00)] “Russell”[Knowledge/Analogy/Induction(89)] summarized. G…P[(77/80)]/“Rumelhardt” “back-propagation”/Umklapp-PIPUB generic localization-criterion via NITS(VS. SR) proves hyperbolic/pink-“noise” PS most-efficient long-distances probe in Vianu[Fdns./Data-Bases(95)] DB networks, and Siegel accelerated-ANN/AI BD/ML/DL-FREE Newcomb(1881)/Bose(24)-Einstein(25) condensation(N/BEC)-“machine” via on-nodes switching-function fermionic to bosonic morphism, models:Turing-(36)-plagiarized (t,r)-Ising(11)-SOL/“energy landscape” (1822)-integral-transforms to (w,k)-Hubbard:“bands NOT bonds”!!! |
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U71.00222: Unitary Mass Representation in the Generalized Newton's Laws Zhi an Luan This paper gives the topological quantum mass representation of New Physics, which is based on a closed twist complex Fu-Xi torus in unitary space-time. It includes 5 mass domains: |
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U71.00223: On light Speed and Electron Speed in Unitary Space-Time Zhi an Luan Using the new transformation group of mass and velocity in the Generalized Newton's Laws (GNL), I have precisely determined a surprisingly reliable and true new theoretical physics scheme: |
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U71.00224: The concept of velocity in the history of Brownian motion - From physics to mathematics and back Arthur Genthon Interest in Brownian motion is shared by different com- |
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U71.00225: GENERAL PHYSICS
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(Author Not Attending)
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U71.00226: Chemistry in Quantum Cavities: Exact Results in Thermal Equilibrium and Modified Dissociation1 Dominik Sidler, Michael Ruggenthaler, Heiko Appel, Angel Rubio In recent years tremendous progress in the field of light-matter interactions has unveiled that strong coupling to an optical cavity can modify chemistry substantially. However, many fundamental questions of chemistry in cavities remain open today. This is also due to a lack of exact results that can be used to validate and benchmark approximate approaches. We provide, to our knowledge, the first exact numerical results for the Pauli-Fierz Hamiltonian of a three-body systems in 3D, coupled to one effective cavity mode. This allows us to investigate the reliability of the ubiquitous Jaynes-Cummings model not only for electronic but also for the case of ro-vibrational transitions of He, H2+ and HD+. We show the emergence of new bound polaritonic states beyond the dissociation energy limit of H2+ and we demonstrate the modification of chemical properties under thermal equilibrium conditions. |
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U71.00227: Postulate I Joel Maker Modern fundamental physics theories such as the Standard Model (SM) contain many assumptions. So where do all these assumptions come from? This is not real understanding. It is curve fitting. So why bother? This theory in contrast has only onesimple postulate: Postulate1. So there is reason to be excited. That is the only postulate since the 1 in the postulate of 1 generates through symbol definitions the 1U1=1+1 list-define algebra natural number underpinning of the rational numbers. These allow us to define the real number 1 from a Cauchy sequence of these rational numbers (Cantor) using iteration zN+1=zNzN+C (1a) and dC=0 (eq.1b). So as C->0, and N->infinity eq.1a turns uniquely into z=zz+C (eq.1) thereby defining real#1 in the postulate of 1 as it must since 1=1X1+0. Alternatively solvethe same eq.1a,eq.1b for C and z(eigenvalues). So plug eq.1 into eq.1b getting Special Relativity(SR) and a unbroken degeneracy Cliffordalgebra. Equation 1a explicitly defines the Mandelbrot set CM (since zN+1finite) with fractal (¼)MMandlebulbs and (1040)NXcosmology. CM turns SR into GR and breaks that 2D degeneracy into a 4D Clifford algebra of Mandlebulbleptons and associated triplets and singlets (i.e., the SM Bosons). Summary: just postulat the real#1 and get both real#math and physics. |
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U71.00228: A Refutation of Special Relativity Eric Samuel This paper presents rigorous arguments in favor of the Newtonian principles of time invariance (TI) and mass invariance (MI), in contention with the special relativity (SR) principles of relativistic time dilation and relativistic mass. Firstly, those ingenious classical experiments in the phenomenological areas of (i) μ- and pi-meson lifetimes (ii) the Compton effect, (iii) positron annihilation, (iv) electron motion in an electric field, (v) electron motion in a magnetic field, and (vi) the transverse Doppler effect, currently upheld as incontrovertibly supporting SR, have been remarkably reinterpreted within the context only of the Newtonian TI and MI principles, and without invoking SR principles. Secondly, several fundamental weaknesses of SR are delineated by careful analyses. Both the experimental and theoretical sets of arguments above lead to the inevitable conclusion that the Newtonian TI and MI principles alone are sufficient to satisfactorily explain known experiments. Crucial implications of excluding SR principles from the framework of fundamental laws, and restoring the universality of the Newtonian principles, will also be discussed. |
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U71.00229: On the Role of Einstein–Cartan Gravity in Fundamental Particle Physics Carl Diether Two of the major open questions in particle physics are: (1) Why do the elementary fermionic particles that are so far observed have such low mass-energy compared to the Planck energy scale? (2) What mechanical energy may be counterbalancing the divergent electrostatic and strong force energies of point-like charged fermions in the vicinity of the Planck scale? In this paper, using a hitherto unrecognised mechanism derived from the non-linear amelioration of the Dirac equation known as the Hehl–Datta equation within the Einstein–Cartan–Sciama–Kibble (ECSK) extension of general relativity, we present detailed numerical estimates suggesting that the mechanical energy arising from the gravitationally coupled self-interaction in the ECSK theory can address both of these questions in tandem. |
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U71.00230: A chain whip in action: surprising dynamics Peter Palffy-Muhoray, Tianyi Guo, Xiaoyu Zheng Chains, consisting of jointed rigid segments, can exhibit fascinating and unexpected dynamic phenomena; one example is the chain fountain [1]. Whips, formed from continuously deformable soft materials, also show interesting dynamical phenomena, such as supersonic tip velocity [2]. In this talk, we identify the processes responsible for the unusual response of these two mechanical systems, and demonstrate surprising dynamics when these are combined in a chain whip. |
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U71.00231: Dark Matter Revealed
Dynamic Gravitation Reveals How Extra Gravity Halos (aka Dark Matter) are Projected from Galactic Cores John Huenefeld The term dark matter presupposes a material cause of the extra gravity observed in galaxies. What is actually observed is an Extra Gravity Halo (EGH). The mysterious source of this extra gravity has now been resolved. |
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U71.00232: Decoherence-Free Entropic Gravity: Model and Experimental Tests Alex Schimmoller, Hartmut Abele, Denys Bondar Erik Verlinde's theory of entropic gravity, postulating that gravity is not a fundamental force but rather emerges thermodynamically, has garnered much attention as a possible resolution to the quantum gravity problem. Some have ruled this theory out on grounds that entropic forces are by nature noisy and entropic gravity would therefore display far more decoherence than is observed in ultra-cold neutron experiments. We address this criticism by modeling linear gravity acting on small objects as an open quantum system. In the strong coupling limit, the entropic master equation recovers conservative gravity. We show that the proposed master equation is fully compatible with the qBounce experiment for ultra-cold neutrons. Furthermore, the entropic master equation predicts energy increase and decoherence on long time scales and for large masses, phenomena which tabletop experiments could test. In addition, comparing entropic gravity's energy increase to that of the Diosi-Penrose model for gravity induced decoherence indicates that the two theories are incompatible. These findings support the theory of entropic gravity, motivating future experimental and theoretical research. |
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U71.00233: Direct relativistic extension of the Schrodinger equation Luis Grave de Peralta, Bill Poirier, Luis A. Poveda Recent results obtained by solving the following relativistic equation for a particle with mass m and spin-0 [1-5]: |
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U71.00234: Direct relativistic extension of the Madelung-de-Broglie-Bohm theories Arquimedes Ruiz-Columbie, Luis Grave de Peralta Non-relativistic Madelung-de-Broglie-Bohm theories result from reformulations of Quantum Mechanics based on the Schrodinger equation. Starting from an intriguing Schrödinger-like equation, which describes a particle with mass and spin-0 and with the correct relativistic relation between its linear momentum and kinetic energy [1-5], the basic equations of the non-relativistic quantum mechanics with trajectories and quantum hydrodynamics are extended to the relativistic domain. Some simple but instructive free particle examples are discussed. This approach differs from other approaches in the simplicity of the deduction of the basic relativistic equations of the extended theories, and in the easier intuitive interpretation of both the basic relativistic equations and the relativistic results obtained using the extended theories. |
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U71.00235: Numerical computing of induction motor model through Levenberg-Marquardt method Hira Ilyas, Iftikhar Ahmad The aim of study is to develop a progressive stochastic numerical solver by means of neural networks through Levenberg-Marquardt backpropagation to examine the dynamics of the higher order nonlinear boundary value problem arising in induction motor model. The fifth order ordinary differential equation dataset is constructed by using Hermite numerical solver and determined the target parameters for continuous mapping of neural networks. The training, testing and validation processes are employed in neural network tool through backpropagation of Levenberg-Marquardt method to estimate the numerical solution of nonlinear induction motor model by constructing different scenarios through varying involved continuous functions on the specific real valued interval. Validation and verification of neural network model is endorsed to calculate the solution of nonlinear induction motor model on the cost of achieved accuracy by histograms error, mean squared error and regression studies. |
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U71.00236: Directional scattering reinforced by acoustic bianisotropy and related acousto-mechanical effects Ivan Toftul, Konstantin Bliokh, Mihail Petrov First order bi-anisotropic effects in linear acoustics are connected with a coupling mechanism between monopole and dipole modes. This phenomena is known as Willis coupling and appeared in literature in 1985 [1]. We note that only recently it had started to receive attention. Also various acousto-mechanical engineering devices were highlighted in the literature, demonstrating precise control of subwavelength particles [2]. |
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U71.00237: Introduction to a Unified Heuristic Quaternal Physics Claude Massot Relativity and Quantum theories remain quite incompatible and forces are not unified. Anti and Dark Matter or Magnetic monopoles are not understood, Quantum computing and supraconductivity require near 0°K. Fermi, in just 4 years did prove nuclear fission, but, so far, all controlled nuclear fusion experimental reactors have failed at producing a first kwh. Physics, despite all its triumphs, is suffering, from its isolation from healthy competition by its total confinement in a hypertrophied Standard Model and its weakening by an opaque, stifling peer review system. Far from these major concerns, my own starting venture toward a New Physics, stemmed from a serendipitous analogy between diphasic and dual wave/particle motions which struck me, in my early scientific career and led to challenge the relativistic base of Physics, with a New Hypothesis of the Complex Nature of Matter. André Lichnérowicz did present it at the French Academy of Sciences in 1994. I have extended it into a quaternion based, new Physics, unifying relativistic with quantum results as well as electromagnetism with strong force and gravitation, defined as a residual purely electric force, modeling photons, electrons and protons with an updated Rutherford/Bohr Model and the neutron as a sub-hydrogen atom. |
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U71.00238: GRB 180720B: A Glitching Giant RAHIM MORADI, LIANG LI, J Ruffini, JORGE ARMANDO RUEDA HERNANDEZ, CARLO LUCIANO BIANCO, NAREK SAHAKYAN, YU WANG GRB 180720B, observed by Fermi-GBM on 20 July 2018 at 14:21:39.65 UT with an isotropic energy of Eiso = 5:92x1053 erg, is classified as a Binary-driven Hypernova of type I (BdHN I). The gravitational collapse of the COcore leads to a supernova (SN) explosion and to a collapsing iron core producing a new NS (νNS). The hypercritical accretion of the SN ejecta onto the νNS leads to a long-lasting X-ray afterglow with a luminosity LX / t-1.48±0.32. We propose that this short-term radiation with energy of ΔEg,rad = 3x1050 erg, occurring during the characteristic time of Δtrec~ 103 s is due to the glitch events caused by the energy of the injected relativistic electrons occurring in the magnetosphere of the νNS during its slowing down. |
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U71.00239: The conical morphology, jetted GeV emission, and X-ray afterglows of long GRBs J Ruffini, RAHIM MORADI, JORGE ARMANDO RUEDA HERNANDEZ, LIANG LI, NAREK SAHAKYAN, YEN-CHEN CHEN, YU WANG, YERLAN AIMURATOV, LAURA MARCELA BECERRA, CARLO LUCIANO BIANCO, CHRISTIAN CHERUBINI, SIMONETTA FILIPPI, MILE KARLICA, Grant James Mathews, MARCO MUCCINO, GIOVANNI PISANI, DARIA PRIMORAC, SHESHENG XUE Context. We review evidence that all short and long GRBs have binary progenitors. Among them, the progenitor of BdHNe consists of a carbon-oxygen core (COcore) and a binary neutron star (NS) companion. For binary periods as short as 5 min, the special energetic subclass BdHN I originates from the COcore collapse. In some cases only, further accretion onto the BH leads to GeV emission with an isotropic luminosity LGeV ∝ t−1.19±0.04. 3) The new NS (νNS)created by the SN accretes SN material giving origin to the X-ray afterglow with LX ∝ t−1.48±0.32, always present in all BdHN I. |
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U71.00240: The inner engine of the high-energy emission of long gamma-ray bursts J Ruffini, JORGE ARMANDO RUEDA HERNANDEZ, ROY PATRICK KERR It has been recently shown that the observed GeV emission can be explained by an electrodynamical process occurring in the “inner engine” of a BdHN: a rotating BH of mass M and angular momentum per unit mass a, embedded in very-low-density ionized plasma and a test, ordered magnetic field, asymptotically aligned with the BH rotation axis and of strength B0. The electric field induced by the magnetic field and the BH rotation, modeled by the Papapetrou-Wald (1974)solution of the Einstein-Maxwell equations, accelerates charged particles of the surrounding ionized plasma in the vicinity of the BH. We show that indeed the electrons accelerate to ultrarelativistic energies radiating high-energy photons. In particular: 1) along the BH rotation axis the electrons can gain up to 1018 eV, implying that GRBs may contribute to the observed ultrahigh-energy cosmic rays; 2) the GeV emission is emitted in a “cone” with approximate semi-aperture angle of 60°, centered on the BH rotation axis; 3) higher energies can be emitted only near to the BH rotation axis at very small angles. For instance, for inner engine fiducial parameters M= 4 M⊙,a / M=0.3, and B0= 1011 G, a power of the order of 1050 erg s−1 is radiated off in the GeV energy domain. |
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U71.00241: Inferences of GRB 190114C for the Crab pulsar and the supernova remnant J Ruffini, RAHIM MORADI, JORGE ARMANDO RUEDA HERNANDEZ, CARLO LUCIANO BIANCO, CHRISTIAN CHERUBINI, SIMONETTA FILIPPI, LIANG LI, NAREK SAHAKYAN, YU WANG The understanding of binary-driven hypernovae of type I (BdHNe I) has identified the central role of the explosion of the supernova (“SN-rise”) as well as of the role of the hypercritical accretion of the SN ejecta onto the binary companion neutron star (NS) and onto the newborn NS (νNS) in determining the GRB dynamics. We model the νNS through the equilibrium sequence of Maclaurin spheroids. By requiring that the νNS period extrapolated on 1000 yr coincides with the one of PSR B0531 + 21 (the Crab pulsar), we determine the initial spin of the νNS to be 0.9 ms, and follow the subsequent rotational and gravitational evolution of the eccentricity. The observed changes in the braking index are proposed to be correlated to pulsar glitches, whose intensities are predicted to be strongly correlated with the pulsar spin. We propose that the progenitor of the Crab nebula and of the Crab pulsar is a GRB very similar to GRB 190114C. |
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U71.00242: Exploring diffraction with a pilot-wave model Giuseppe Pucci, Antoine Bellaigue, Anand Uttam Oza The seminal experiments of Yves Couder and Emmanuel Fort demonstrated that a droplet walking on the surface of a fluid bath may exhibit behavior thought to be peculiar to the quantum realm. One of their experiments suggested that single-particle diffraction and interference may be obtained when a walker crosses a single- or a double-aperture between submerged barriers (Couder, Y. & Fort, E. Phys. Rev. Lett. 97, 154101, 2006). Later experiments with finer control of experimental parameters yielded different results, thus reopening the question of the extent of the analogy between walkers and quantum particles (Andersen, A. et al. Phys. Rev. E 92, 013006, 2015; Pucci, G. et al. J. Fluid Mech. 835, 1136-1156, 2018; Rode, M. et al. Phys. Rev. Fluids 4, 104801, 2019). Here we use the pilot-wave model developed by Oza et al. (J. Fluid Mech. 737, 552-570, 2013) to explore the diffraction of a two-dimensional, wave-piloted particle by one-dimensional barriers. While our results are generally different from the Fraunhofer diffraction patterns in optics, the statistical distribution of deflection angles generally exhibits multiple peaks, the number of which depends on the obstacle geometry. |
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U71.00243: The Ideas of Particle Physics : four decades past and the next James Dodd
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U71.00244: Point Particle Dynamics from Geometric Paths Thomas Barnebey A rudimentary model universe is formulated from gravitational and electromagnetic fields. Quantum mechanics and the subatomic interactions described through quantum mechanics are not included in the model. The behavior of the system is determined by an invariant action which includes contributions characterizing paths through the fields. No particles are assumed á priori. The existence of point particles, together with their structures as delta function densities, arises from the equations of motion of the system, and particle masses appear as integration constants of the path equations. The derived masses act as sources of the gravitational field, as well as measures of inertia. A modified Nordström/Reissner metric describes the gravitational field of each particle. The particles exhibit characteristics qualitatively similar to the properties of observed fundamental particles. |
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U71.00245: Why is the speed of light what it is? David E Pressler Albert Michelson – Edward Morley (circa 1887) tried to establish the fact that an invisible ubiquitous medium called “luminiferous ether” exists. However; when their unsuccessful efforts were determined and hypothesized it became known as the most famous failed experiment in the history of science. The interferometer device that was used consisted of two mirrors which allowed a light source to be split in two orthogonal light beams by a half-silvered mirror such that the beam of light in the direction of motion would arrive a bit slower than the beam arriving perpendicular to the hypothetical ether-wind. When analyzed, the light should have shown up as a distinctive pattern of interference. This turned out to be a null result – there was absolutely no interference pattern. Pressler’s new paradigm shift, perhaps the most important in the history science, is that both mirrors move synchronously towards the center of the interferometer. Particle physicists attest to the supporting empirical evidence – the faster particles are accelerated the smaller they become. The solid space medium is a perfect elastic solid. The M-M theory is a marvelous success. |
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U71.00246: Self-Organization In Stellar Evolution: Nucleosynthesis and its Size Dependence Georgi Georgiev, Travis Butler An open question is how complex systems self-organize to produce emergent structures and properties, a |
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U71.00247: A new explanation for the color variety of Photons and the continuous coordination between wavelength, amplitude and frequency Gh. Saleh, M.J. Faraji, Reza Alizadeh, Mehdi Abdi Shahshahani, Adel Karimi Ansari Physicists have always used the existing coordination between the phenomena of the universe to discover the relationships and advance the Science. |
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U71.00248: A new Theory of the Interaction of the fields of Massive Particles Richard Kriske The fields of massive bodies undergo Lorentz Contraction, when they move, or the Doppler Effect when they are massless. When a massive particle, such as a Proton nears the speed of light, the Proton flattens due to Lorentz Contraction. Einstein claimed that, the Lorentz Contraction of the Electron was proof that the Electron was held together by Gravity, as the Lorentz Contraction is not in Maxwell's Equations, but is due to the General Theory of Relativity. Special Theory of Relativity, also has the Doppler Effect, that was originally championed by Ernst Mach. Although Einstein took the Doppler Effect as being fundamental to Relativity, he did not, at least in any work that I am fimiliar with claim that the Electromagnetic Field underwent the Lorentz Contraction, as that would mean that Photons are held together by Gravity as well. So direct hits of particles on target are not necessary. Other fields may travel with the particle. This glancing effect is already seen in the production of positrons from surfaces. Also one could deduce that the reason the W particle is massive and may be flattened to a pancake. This is an exciting Theoretical breakthrough, in that it may be possible to accelerate W particles and through glancing generate hidded fields and perhaps the Higgs field. |
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U71.00249: Many Physics Formulas May Need Updating With The Addtion of Rotation And Vibration Kinetic Energy Factors Discovered Necessary In The Last Century As Possible Conditions Of All Matter As Well As Only Previously Known Linear Kinetic Energies. Future Physics Formulas May Need
Addition Of Rotation and Vib Stewart Brekke About 1960 it was found that all matter such as molecules, nuclei, stars and planets, besides moving linearly, may also rotate and vibrate. Many older physics formulas did not include these essential factors.and may need updating as well as future ones. |
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U71.00250: New Experimental Phenomena That Thought Waves Remotely Changed The Photo-Voltages At Same Rate Dayong Cao In our experiments, the light of the lamp radiated on four solar cells to produce four photo-voltages such as V1, V2, V3, V4. |
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U71.00251: Women Supporting Women in the Sciences: Implementation of professional development workshops aimed at empowering women and girls in Tanzania Jill Wenderott, Joyce Elisadiki Women in science, technology, engineering, and mathematics (STEM) fields are underrepresented across the world, making up about 29% of the STEM workforce [1]. Improving this representation potentially requires a myriad of approaches, including spurring elementary- and secondary-level girls' interests in STEM and promoting the retention of women studying STEM at the university level. With these approaches in mind, Women Supporting Women in the Sciences (WS2) began as a collaborative effort between Northwestern University and several universities in Tanzania (TZ) in late 2018. The overarching mission of WS2 is to leverage past experiences and shared resources to work together, learn from each other, and support women in STEM globally. In early 2019, WS2 created curricula for professional development workshops focused on (1) career development and (2) organizing as women in STEM. These two workshops were designed for secondary- and university-level students, and upon finalization, TZ facilitators were trained on the workshop content via virtual meetings. This talk will discuss the two workshops created by WS2, as well as outcomes to date from their implementation in TZ in late 2020 and long-term goals of the WS2 program. |
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U71.00252: International Society of Muslim Women in Science Sultana Nahar The International Society of Muslim Women in Science (ISMWS) was founded in |
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U71.00253: High Resolution Imaging through Structured Illumination in Lens-less Incoherent Microscopy Aqiba Hafeez, Iqra Bashir, Ahsan Mehmood Khan, Anwar Hussain Lens-less microscopy using sinusoidal structured illumination to attain high resolution and large field of view is the main target of this project. The schematic includes an LED,followed by a Spatial Light Modulator,a USAF resolution chart,and CMOS sensor respectively.Structured Illumination is carried out by using an incoherent light,LED,as illumination source.The illumination light is modulated sinusoidally by using a Spatial Light Modulator.Sinusoidal illumination pattern having cosine waves with three different phase shifts is generated in MATLAB and then assigned to SLM to downmodulate higher spatial frequencies.The sample information is recorded on sensor without using any objective lens.To retrieve the sample information,from captured raw images corresponding to each phase shift,backward propagation model is applied using MATLAB.Phase and amplitude information of sample is obtained from the final reconstructed image.The project aims to design a lens-less microscope with high resolution,portability,large field of view and depth of field,compared with conventional microscopes.This technique has many common applications in biomedical engineering for cellular studies.In future,lens-less microscopy might replace optical microscopy due to its simplicity and cost-effectiveness. |
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U71.00254: The network structure of scientific revolutions Harang Ju, Dale Zhou, Ann Sizemore Blevins, David Lydon-Staley, Judith Kaplan, Julio Roberto Tuma, Danielle Bassett Philosophers of science have long postulated how collective scientific knowledge grows. Empirical validation has been challenging due to limitations in collecting and systematizing large historical records. Here, we capitalize on the largest online encyclopedia to formulate knowledge as growing networks of articles and their hyperlinked inter-relations. We demonstrate that concept networks grow not by expanding from their core but rather by creating and filling knowledge gaps, a process which produces discoveries that are more frequently awarded Nobel prizes than others. Moreover, we operationalize paradigms as network modules to reveal a temporal signature in structural stability across scientific subjects. In a network formulation of scientific discovery, data- driven conditions underlying breakthroughs depend just as much on identifying uncharted gaps as on advancing solutions within scientific communities. |
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U71.00255: Collaring the Standard Model Knute Thorsgard Despite progressing well, when collars don't meet, it becomes necessary to start over. Relativity and Quantum Electrodynamics, the collars of the Standard Model of Theoretical Physics, don't meet. "Can't begin so can't finish" combined with "all those perspectives are equally valid" leaves the collars lopsided. |
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U71.00256: Variability of particulate matter in Kathmandu and Pokhara Valley using Purple Air Sensor and an Overview of Origin of Pollutants Jeevan Regmi, Khem Narayan Poudyal, Amod Pokhrel, Katrina Wilson, Rudra Prasad Aryal The concentration of fine and coarse mode particulate matters at the surface level over two major cities, Pokhara and Pulchowk of Nepal, were observed from January to September of 2020 by using particulate matter sensors. The hourly and daily averaged size segregated particulate matters of different size distributions are obtained for analysis. We have also compared the column-averaged aerosol optical depth (AOD) obtained from AERONET site. The average concentration of PM 2.5 was higher during the winter season, 99.64 μg/m3 and pre-monsoon season, 55.94 μg /m3 in Pulchowk and it was 58.96 μg/m3 and 38.50 μg/m3 in Pokhara. On February 1, the concentration of PM 2.5 raised to 201 μg /m3 in Pulchowk and 108 μg /m3 in Pokhara in the morning, whereas on April 11, it was 255 μg /m3 in Pulchowk and 238 μg /m3 in Pokhara in the morning. These data show that particulate matter concentration might have been significantly affected by traffic activities, and even cooking activities in the evening and morning along with the temperature. It is also observed that the data concentration is degrading particulate during precipitation, which was estimated by comparing data with the relative humidity observed by the sensor and precipitation amount over Pokhara. |
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U71.00257: Laboratory studies of Optical aProperties of Biomass Burning Aerosols from Sub-Sharan Africa Biomass fuels and impact on climate Solomon Bililign There are many fuels used for domestic purposes in east Africa, producing a significant atmospheric burden of the resulting aerosols, which includes biomass burning particles. However, the aerosol physicochemical properties are poorly understood. An accurate measurement of optical properties of aerosols is critical for quantifying the effect of aerosols on climate and air quality. Uncertainties persist and measurement results vary significantly. Biomass burning (BB) aerosols have been extensively studied through both field and laboratory environments for North American fuels to understand the changes in optical and chemical properties as a function of aging. There is a clear research need for a wider sampling of fuels from different regions of the world for laboratory studies. We reports work in our laboratory that represents the first laboratory study the optical and chemical properties of wood fuel samples used commonly for domestic use in east Africa. |
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U71.00258: Fundamental Interactions of Nature and Classical Unification of Electromagnetic and Gravitational Forces Alfred Mishi We have looked at the four fundamental interactions, the interaction between imaginary energies. We also have presented a Classical theory of unification of gravitational force and the electromagnetic force based on generalization of Newton’s law of gravitation to include a dynamic term inferred from the Lorentz force of electromagnetic interaction. This dynamic term alone in the gravitational force is enough to develop the entire dynamic theory of gravitation parallel to that of electrodynamics. It has been shown that the inverse square law of the static and the dynamic forces is the result of the conservation of mass (Gauss’s Law) and the total momentum (Wang’s Law). The Wang’s Law been a new discovery. The new theory also predicts that the gravitational force is transmitted through propagation of gravitational waves at the speed of light. |
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U71.00259: A non-local thermometer based on Coulomb coupled systems Sagnik Banerjee, Aniket Singha We propose a design for non-local cryogenic electrical thermometer based on Coulomb-coupled systems. The proposed thermometer relies on electrostatic interaction between capacitively coupled quantum dots, resulting in a overall change in conductance due to change in the remote reservoir temperature. Analyzing the performance and regime of operation, we conclude that the the proposed design ensures a superior temperature sensitivity and robustness compared to a simple thermometer consisting of two Coulomb coupled quantum dots. At the end we investigate the regime of operation and comment on the ground state configuration for optimal operation of the proposed thermometer. The design proposed in this paper can be employed to construct highly efficient non-local cryogenic thermometers. |
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U71.00260: Sublimination of van-der-waals bounds by matching the molecular vibration frequency equivalent of a given solid’s molecular latent heat of vaporization. Marc Banks This research is preliminary and consist largely of deductive reasoning. While empirical work was conducted it, was in the early stages and the data that was collected is limited. The snow is not an easy prospect to deal with when it piles up. This is a challenge when you have a disability and, or are elderly. The physics is straightforward, snow is held together by van der waals bonds. To overcome the bonds the molecules must overcome the latent heat of fusion. This equation of pressure and temperature, along with utilizing as little energy as possible, has led me to the following hypotheses. As energy is increase, so will the molecule’s vibrations. By analyzing the vibrations at the various points of the scale of the latent heat of fusion for that substance, in this case snow. It is hypothetically possible to catalog the frequencies of those vibrations. Then deliver the desired frequencies to that substance again, in this case snow. It would not be necessary for the snow to gradually melt through the changing of the seasons, but the required frequencies say for example of vaporization to be deliver to the snow, by some adequate means, say for example a laser beam. This has the potential of inducing sublimination to any substance. |
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U71.00261: Real-Time Tracking and Quantification of Transposible Element Activity Davneet Kaur, Gloria Lee, Nicholas Sherer, Elliot Urriola, Hneil Kim, Chi Xue, Michael Martini, Nigel Goldenfeld, Thomas E Kuhlman Transposable elements (TEs), or jumping genes, are DNA sequences that can change their position in a genome using a cut-and-paste or copy-and-paste mechanism. They are fundamental building blocks of all genomes, accounting for large fractions of genomic masses, and may have played a major role in the emergence of biological structure, diversity and function. Even so, many open questions remain regarding their differential abundance among organisms, the functions of their proteins, rates of activity and transposition and their effects on their hosts. Traditional techniques for measuring TE activity rely on endpoint or periodic population samplings that require activity rates to be interpreted through models of population growth that may not be correct. We overcome these limitations by making real time observations of protein expression and transposition events as they occur in living cells through high resolution fluorescence visualization and quantification techniques. Based on our measurements, we shed light on the differential abundance of TEs and their rates of activity. |
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U71.00262: Effects of of Energy Transfer and Spin-Dependent Processes on Photoluminescence in Rubrene/Alq3 Thin-Films Yoong Phang Rubrene (5,6,11,12 tetraphenylnaphthacene) molecules uniquely exhibit strong singlet fission and triplet fusion processes. Such properties have been impactful in achieving high performance organic light emitting diodes (OLED) and solar cells (OSC). Researchers have discovered that blending rubrene in Alq3 (tris-(8-hydroxyquinolato) aluminum) achieves a benchmark photoluminescence quantum efficiency (PLQE) of 100%. However, the mechanisms contributing to its high PLQE as an acceptor in energy transfer processes have not been addressed. In this project, amorphous rubrene-doped Alq3 films were fabricated in guest concentrations from 1 to 50 wt%, and the emission mechanisms of these donor-acceptor systems were studied with three distinct spectroscopic methods. In particular, the behavior of spin-dependent processes and relative singlet/triplet populations were studied by power-dependent magneto-photoluminescence, while the energy transfer efficiency and dynamics were understood by time-resolved photoluminescence and transient photo-induced absorption. The results of this study provide a fundamental description of the large PLQE measured in these thin-films, which can potentiate improvements in the power-conversion quantum efficiency of OSCs and have further applications in OLEDs. |
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U71.00263: Synthesis and Characterization of Fe-Fe3O4 “Core-Shell” Nanoparticles in carbon matrix Gayane Chilingaryan, Narek Sisakyan, Armine Ginoyan, Eduard Sharoyan, Harutyun Gyulasaryan, Aram Manukyan, Luis Fernando Valencia, Jennifer Gray, Kevin Castillo, Armen Kocharian Carbon coated Fe nanoparticles have been synthesized using solid-phase pyrolysis of iron phthalocyanine (FeC32H16N8) at high temperature (1000°C). The product of pyrolysis additionally annealed at 250°C under the oxygen media allows to produce Fe3O4 shell architecture over Fe nanoparticles. The weight percentage of Fe-Fe3O4 core-shell nanoparticles in carbon matrix is about 13 wt.%. Changing the pyrolysis conditions, it is possible to vary sizes of nanoparticles from 5 to 100 nm. The quantitative composition of the "core-shell" was controlled by changing the concentration of oxygen. Complex structural investigations of these materials are obtained using HRTEM, STEM, X-ray diffraction (XRD) and Raman spectrometers. |
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U71.00264: Dermal fibroblasts and breast cancer cells differentially alter their local stiffness landscape Alicja Jagiello Bulk measurements of ECM stiffness are commonly used in mechanobiology. However, peri-cellular stiffness can be quite heterogenous and divergent from the bulk properties. Here, we use optical tweezers active microrheology (AMR) to quantify how dermal fibroblasts (DFs) and human breast cancer cells MDA-MB-231 (MDAs) embedded in 1.0 and 1.5 mg/ml type 1 collagen (T1C) hydrogels establish dissimilar patterns of peri-cellular stiffness. We found that DFs increase local stiffness of 1.0 mg/ml T1C hydrogels, but surprisingly do not change the stiffness of 1.5 mg/ml T1C hydrogels. In contrast, MDAs largely do not alter stiffness of T1C hydrogels, as compared to cell-free controls. Results suggest that MDAs adapt to the bulk ECM stiffness, while DFs regulate local stiffness to levels they intrinsically “favor”. Further, cells were subjected to treatments that were previously shown to regulate migration, proliferation and contractility of DFs and MDAs. Following treatment, cells established different levels of stiffness magnitude and anisotropy, which were dependent on the cell line, T1C concentration and treatment. In summary, our findings demonstrate that AMR reveals otherwise masked mechanical properties such as spatial gradients and anisotropy. |
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