Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q70: Frontiers of Topological Materials: Synthesis, Prediction, and CharacterizationFocus Recordings Available

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Chair: Jiaqiang Yan, Oak Ridge National Laboratory Room: Hyatt Regency Hotel Jackson Park B 
Wednesday, March 16, 2022 3:00PM  3:36PM Withdrawn 
Q70.00001: Synthesis of bulk topological materials Invited Speaker: Robert J Cava For me, fields are best to work in when new theory, experimental characterization and materials discovery happen simultaneously. That was the case in topological materials research, and its fair to assume that this coupling will happen in several unimaginable or barely imaginable areas of science during your research lifetime. (So “be true to yourself, and never give up” is still the best advice that survivors can give to young scientists in my opinion.) Current efforts in topological materials largely appear to center on the elucidation of what from my perspective appear to be complex issues in new physics, and thus are more difficult for materials chemists to find things to do that are both chemically and physically interesting. Although materials chemists can make thin layers of previously known materials specifically for physicists to study, “where is the chemistry in that” can sometimes be heard sotto voce in the chemistry community about that kind of work. Those things being said, the collaboration between theoretical and experimental physicists, crystal growers and materials chemists to invent, grow, and experimentally explore he properties of materials that have the potential to display new physics has proven to be very productive, and should best continue. Aside from my personal views of research at the chemistry/physics interface, my idea for this talk is to show how chemical and materials science views of materials discovery and optimization can be applied to materials hosting topological electronic states. Since some of you have not yet taken your personal shot at some of the materials of interest for the development of topological physics, there may be materials of interest to your work presented here. 
Wednesday, March 16, 2022 3:36PM  3:48PM 
Q70.00002: Innovative Electron Probe Methods for van der Waals Heterostructures Topological Materials Discovery David C Bell, Austin Akey, Joseph G Checkelsky, Aravind Devarakonda, Cigdem OzsoyKeskinbora New Topological Insulators (TI) quantum materials with interesting/useful properties has caused great excitement and promises to transform device design and computation. Remarkably, some of the quantum phenomena displayed by these materials now persists at room temperature, opening the way for usable devices. 
Wednesday, March 16, 2022 3:48PM  4:00PM 
Q70.00003: Nonlocal Measurement as a Probe of the Spin Hall Effect in Topological Insulators Jennifer E DeMell, Gregory M Stephen, Owen Vail, Aubrey T Hanbicki, Patrick J Taylor, Adam L Friedman Topological insulators (TIs) are promising candidates for alternative computing device designs. In particular, they have great potential for spintronic devices, where utilization of electron spin rather than charge would allow for lowerpower and higherperformance computing in nextgeneration architectures. Efficient conversion between spin and charge signals is crucial to spintronic technology. TIs provide highly efficient spintocharge conversion, as a result of their unique topological properties. One way to electrically quantify conversion efficiency is with the spin Hall effect (SHE). Here, we present SHE measurements of the topological insulator Bi_{2}Te_{2.5}Se_{0.5}. Because of the topological nature of this material, we can measure the SHE without the use of ferromagnetic injectors or detectors. Using the nonlocal resistance, we measure spin Hall angles up to 2.4 with spin lifetimes up to 9 ps. Furthermore, ferromagnetfree measurement allows for quick diagnostics of the spin properties without the need to fabricate multilevel devices. 
Wednesday, March 16, 2022 4:00PM  4:12PM 
Q70.00004: High mobilities and exotic anisotropic magnetoresistivity in the Ir3Ge7 structure family of compounds Aikaterini Flessa Savvidou, Brian W Casas, Xiaofeng Qian, Judy Clark, Michael Shatruk, Luis Balicas We synthesized via an indium flux method a single crystal Pd_{3}In_{7} compound that belongs to the cubic Ir_{3}Ge_{7} structure type and we explore its interesting topological behavior. This family of compounds has shown to be a promising candidate to explore the result of a complex Diraclike electronic structure close to the Fermi level. In the case of Pd_{3}In_{7}, the electronic structure displays multiple band crossings close or on the Fermi energy ε_{F}, leading to Dirac typeI and typeII nodes. The analysis of the quantum oscillations due to the de Haas van Alphen effect (dHvA effect) indicates light effective masses of the order of 0.15m_{e} and very high carrier mobilities, 3000 cm^{2}/V*s, consistent with what is expected from a Dirac material. Notably, the magnetoresistance shows a strong anisotropic behavior as a function of position, even though during the whole rotation the magnetic field is always perpendicular to the direction of the current, leading to a maximum Lorentz force. 
Wednesday, March 16, 2022 4:12PM  4:24PM 
Q70.00005: 'Growth and Characterization of Pure and Doped Topological Material CoSi' Emerson Hemley, Atsutoshi Ikeda, Johnpierre Paglione In CoSi, nontrivial topology and chirality give rise to intriguing physics, such as hosting Weyl fermions, and making it a potential candidate for displaying the quantized circular photogalvanic effect (CPGE). The CPGE is predicted to be quantized in terms of fundamental constants in Weylsemimetals whose topological nodes lie at different energies, but has not been experimentally observed. But to experimentally realize this phenomena, the Fermi energy of CoSi must be tuned precisely. To this end, we report the growth and characterization of pure and electron doped CoSi. Ni and P substituted CoSi single crystals are synthesized via flux method and characterized by xray diffraction and energy dispersive xray spectroscopy (EDX). The Fermi surface and carrier mobility are assessed through quantum oscillations and Hall effect. 
Wednesday, March 16, 2022 4:24PM  5:00PM 
Q70.00006: Exotic weak topological state in RhBi2 Invited Speaker: Thais Victa Trevisan In contrast to the ubiquity of strong topological insulators, material realizations of weak topological insulators (TIs) remain largely elusive due to the inherent challenge of detecting their nontrivial surface states. The tailored synthesis of new materials is a promising path to reduce the experimental gap between strong and weak TIs, and can also lead to the discovery of novel quantum phenomena. Combining material synthesis, ARPES measurements, and analytical modeling, we report the discovery of a weak topological insulating state in triclinic RhBi_{2}. In this talk, we show that the low crystal symmetry 1 of this material allows for additional exotic features in the nontrivial surface state dispersion. In particular, two saddle points develop in the proximity of the surface Dirac cone, leading to a van Hove singularity in the surface density of states that is expected to dramatically enhance the effect of electronic interactions and potentially drive the systems towards manybody instabilities. As an example, we discuss how surface superconductivity is favored in the weak TI surface state of RhBi_{2} as the chemical potential is tuned across the van Hove singularity. The proximity of saddle and Dirac points to the Fermi level makes RhBi_{2} is a promising platform to investigate the interplay between electronic correlations and topological surface states. 
Wednesday, March 16, 2022 5:00PM  5:12PM 
Q70.00007: Fermi surface studies of typeII Dirac semimetal candidate NiTe_{2} using de Haasvan Alphen oscillations Thinh Nguyen, Luminita Harnagea, Duncan Miertschin, Bal K Pokharel, Dragana Popovic, David E Graf, Keshav Shrestha We have investigated the Fermi surface of the typeII Dirac semimetal candidate NiTe_{2} using torque magnetometry. The torque signal measured under applied fields of 35 T and temperatures down to 0.32 K shows clear de Haasvan Alphen (dHvA) oscillations. The oscillations are welldefined and consist of two major frequencies F_{1} ~ 100 T and F_{2} ~ 400 T. To investigate the properties of the Fermi surface, we have carried out measurements of angular and temperature dependence of the dHvA oscillations. Both frequencies vary while increasing the angle between the sample surface and the magnetic field. Also, the amplitude of the oscillations decreases at higher temperatures. We have analyzed the temperaturedependent dHvA data using the LifshitzKosevich theory and calculated several physical parameters characterizing the Fermi surface. 
Wednesday, March 16, 2022 5:12PM  5:24PM 
Q70.00008: Thermoelectric and thermomagnetic transport in triplepoint topological metal Molybdenum Phosphide (MoP) Abhishek Saini, Chenguang Fu, Safa Khodabakhsh, Ashley E Paz y Puente, Claudia Felser, Sarah J Watzman MoP is a topological metal which had been shown to host a triple point fermion in its band structure with a Weyl point in the bulk bands [1]. This complex band structure is a strong motivation for studying electrical and thermal transport. Singlecrystalline MoP previously demonstrated an extremely high electrical conductivity and the potential for hydrodynamic charge flow [2]. In this work, both the Seebeck effect and Nernst effect are investigated for the first time in polycrystalline MoP samples. Additionally, thermal conductivity, electrical resistivity, heat capacity, and the Hall effect are determined as functions of grain size, temperature, and magnetic field. Compared to singlecrystalline MoP [2], both thermal and electrical conductivity are found to be 12 orders of magnitude smaller in polycrystalline samples. From WiedemannFranz law analysis, electronic and phonon thermal conductivity are determined, and the former is found to be dominating at higher temperatures. This is contrary to the singlecrystalline MoP, due to more scattering of phonons. Other transport properties show typical metallic behavior with relatively small Seebeck and Nernst effects due to a large charge carrier density. 
Wednesday, March 16, 2022 5:24PM  5:36PM 
Q70.00009: Fermi surface studies of typeII Dirac semimetal ZrTe_{2 }using torque magnetometry Keshav Shrestha, Niraj Aryal, Luminita Harnagea, Thinh Nguyen, Duncan A Miertschin, Bal Pokharel, Dragana Popovic, David E Graf The transition metal dichalcogenides (AX_{2}, A = Mo, W, Ta, Zr, Hf, etc., and X = S, Se, or Te) are interesting as they provide platforms for exploring rich and tunable physical properties such as charge density wave, superconductivity, nontrivial band topology, etc. Here, we have explored the Fermi surface of ZrTe_{2 }using torque magnetometry with applied fields up to 35 T and temperatures down to 0.32 K. Our torque data show de Haasvan Alphen (dHvA) oscillations with two distinct frequencies at 88 T and 530 T. The angular and temperature dependence of the oscillations was performed to understand the Fermi surface properties. Also, the density functional theory calculations were carried out to explain our experimental results. We found that the angular dependence of the observed frequencies agrees with our firstprinciples calculations. 
Wednesday, March 16, 2022 5:36PM  5:48PM 
Q70.00010: Large gap highorder topological insulators in superatomic graphene Yinong Zhou, Feng Liu, Ruqian Wu Highorder topological insulators (HOTIs) have been investigated in several twodimensional (2D) lattices. The inter and intrahexagon hopping in a Kekulé lattice opens a nontrivial gap protected by the lattice symmetry, leading to the zerodimensional corner states. However, the realization of the 2D HOTI is still challenging because of the limit of material candidates and the weak signal of the corner states. Here, we introduce the onsite Coulomb repulsion (U) in the Kekulé lattice to enlarge the topological gap. We found that the corner states become more localized, and the intensity of the corner mode is significantly enhanced. We further proposed a series of superatomic graphene lattices superimposed on a Kekulé lattice for the realization of large gap HOTIs with different U/t ratios. Our results provide a promising strategy to generate strong topological corner states. 
Wednesday, March 16, 2022 5:48PM  6:00PM 
Q70.00011: Metalinsulator transition in Fedoped typeII Weyl semimetal WTe_{2} Rabindra Basnet, Krishna Pandey, Gokul Acharya, Md Rafique Un Nabi, Aaron M Wegner, Cory B Stephenson, Samuel Bishop, Jin Hu The metalinsulator transition (MIT) has been a subject of intensive study in condensed matter physics for decades, providing opportunities to study fundamental physics as well as develop novel switching devices based on multiple resistance states. Doping has been known as an effective tunable parameter to manipulate the MITs. Here we report the Fe doping in WTe_{2}. We characterized the structure, transport, and thermodynamic properties of Fedoped WTe_{2} single crystals, and found signatures of Kondo localization and MIT. Therefore, this material system offers a fascinating platform to explore emergent quantum phenomenon introduced by magnetic doping in a Weyl semimetal. 
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