Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session U64: Topological Materials: Majoranas and NonConventional Topological StatesFocus

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Sponsoring Units: DMP Chair: Gaurab Rimal, Rutgers University, New Brunswick Room: Mile High Ballroom 4E 
Thursday, March 5, 2020 2:30PM  3:06PM 
U64.00001: Signature of Dispersing 1D Majorana Channels in an Ironbased superconductors Invited Speaker: Zhenyu Wang Selected by Focus Topic Organizer (Seongshik Oh and Peter Armitage) 
Thursday, March 5, 2020 3:06PM  3:18PM 
U64.00002: Physical Properties of XTSb[(X= Eu, Sr), (T= Ag, Au)] single crystals Parul DEVI, LinLin Wang, Caiden Abel, Sergey L. Bud'ko, Paul C Canfield Single crystals of XTSb [(X= Eu, Sr), (T= Ag, Au)] were grown by the solution growth by using self flux [1]. These single crystals were investigated by powder Xray diffraction at room temperature and the structure was successfully refined to be the hexagonal (space group P63/mmc) crystal structure . Temperature dependent magnetic susceptibility measurements indicate antiferromagnetic ordering for magnetic compounds (e.g. T_{N} = 6 K for EuAgSb). Density functional theory calculations find that the band inversion giving a Dirac point is present in the nonmagnetic Au compounds, but not the Ag compounds. Thermodynamic and transport data on the nonmagnetic SrAgSb, SrAuSb and magnetic EuAgSb, EuAuSb will be presented and compared. 
Thursday, March 5, 2020 3:18PM  3:30PM 
U64.00003: Ab initio study of surface states in Bi_{4}Te_{3} Omar Ashour, Zhenglu Li, Steven Louie The crystal structure of the layered material Bi_{4}Te_{3}, a member of the adaptive series of crystals (Bi_{2})_{m}(Bi_{2}Te_{3})_{n}, forms a superlattice of alternating Bi_{2} and Bi_{2}Te_{3 }layers. Given the topological properties of its individual constituents, Bi_{4}Te_{3} is expected to be a topological insulator or semimetal. Recent experimental results indicate the presence of unusual surface states in this material. In this work, we perform ab initio density functional theory calculations of bulk and slab geometries to investigate the surface states of Bi_{4}Te_{3}. 
Thursday, March 5, 2020 3:30PM  3:42PM 
U64.00004: Bond Disproportionation in the Silver Bismuthate Ag_{2}BiO_{3} Mohamed Oudah, Minu Kim, Ksenia Rabinovich, Graham McNally, Berkay Kilic, Kathrin Küster, Robert Green, Kateryna Foyevtsova, Alexander Boris, George Albert Sawatzky, Andreas P Schnyder, Douglas Andrew Bonn, Bernhard Keimer, Hidenori Takagi The stoichiometric silver bismuthate Ag_{2}BiO_{3} is expected to contain bismuth in the nominal Bi^{+4} state, but the bismuth ions disproportionate into two distinct sites that render Ag_{2}BiO_{3} insulating [1]. Recent theoretical predictions of metalinsulator transition and Weyl semimetal state in Ag_{2}BiO_{3} have revived the interest in this material [2]. However, such novel properties are only expected in the absence of disproportionation of bismuth, where Ag_{2}BiO_{3} is in the Pnna phase. Here, we examine nature of disproportionation in Ag_{2}BiO_{3} via Xray absorption and photoemission spectroscopies. We present an updated band structure for Ag_{2}BiO_{3 }in the Pnn2 (disproportionated) phase, where we have a band gap of 1 eV in agreement with our optical spectroscopy measurement. Furthermore, we present Raman spectroscopy results and highlight the extent of similarities to other disproportionated bismuthates despite the distinct crystal structure Ag_{2}BiO_{3}. 
Thursday, March 5, 2020 3:42PM  3:54PM 
U64.00005: Analytic calculation of generalized Brillouin zone in nonHermitian bands Zhesen Yang, Kai Zhang, Chen Fang, Jiangping Hu In this talk, we introduce a systematic method to calculate the generalized Brillouin Zone (GBZ) analytically in one dimensional nonHermitian systems. In general, a mband nonHermitian Hamiltonian is constituted by m distinct subGBZs, each of which is a piecewise analytic closed loop. All the analytic properties of the GBZ can be characterized by an algebraic equation, which is dubbed as auxiliary GBZ. As an application of our theory, we show a new kind of topological phase under open boundary condition, which is characterized by the nonzero energy winding number for each band. 
Thursday, March 5, 2020 3:54PM  4:06PM 
U64.00006: Materials database development for electromagnetic responses Yan Sun, Yang Zhang, Qiunan Xu, Jonathan Noky, Jakub Zelezny, Klaus Koepernik, Tomas Jungwirth, Jeroen Van den Brink, Claudia Felser The interplay between electromagnetic response theory and symmetry is crucial to understand the transport properties in quantum materials. It is critical to fully understand these physical properties and find materials that host strong electromagnetic response, which, have an extensive impact on the development of data storage, information processing, and energy conversion, etc. Experimentally, however, such largescale screening is very impractical, as a quantitative determination of the electromagnetic responses by electrical and optical measurements requires integrating each material separately into a complex multicomponent mesoscopic transport device. Theoretically and computationally, the situation is in principle much more straightforward. Via high throughput numerical simulations, we developed the database for intrinsic spin Hall effect in nonmagnetic compounds, shift current in inversion symmetry Weyl semimetals, anomalous Hall effect and anomalous Nernst effect in magnetic Heusler compounds based on the known materials. Our database is helpful for the full understanding of the electronic properties of materials and selecting the correcting materials for further experimental studies. 
Thursday, March 5, 2020 4:06PM  4:18PM 
U64.00007: Reentrant Defect Modes in a PTSymmetric Circuit Alexander Stegmaier, Tobias Helbig, Tobias Hofmann, Ronny Thomale Systems obeying PTsymmetry are a special case in nonHermitian physics where real eigenvalue spectra can still emerge. They usually exhibit a phase diagram with different regimes of symmetry conservation or spontaneous symmetry breaking in their eigenstates. We examine a localized zeroenergy defect mode within a PTsymmetric hopping model that disappears and reemerges at different PT phase transitions and present an exhaustive explanation for this phenomenon. Our theoretical findings are confirmed by eigenstate measurements for different gain/loss profiles in an electrical circuit implementation. 
Thursday, March 5, 2020 4:18PM  4:54PM 
U64.00008: Distinct multiple fermionic states in a single topological metal Invited Speaker: Madhab Neupane Among the quantum materials that have recently gained interest are the topological insulators, wherein symmetryprotected surface states cross in reciprocal space, and the Dirac nodalline semimetals, where bulk bands touch along a line in momentum space. However, the existence of multiple fermion phases in a single material has not been verified yet. Using angleresolved photoemission spectroscopy (ARPES) and firstprinciples electronic structure calculations, here we discuss a systematic study of the metallic ternary material discovering properties, which are unique in a single topological quantum material. We experimentally observe weak topological insulator surface states and our calculations suggest the existence of additional strong topological insulator surface states. Our firstprinciples calculations reveal a onedimensional Dirac crossing—the surface Diracnode arc—along a highsymmetry direction, which is confirmed by our ARPES and timeresolved ARPES measurements. Furthermore, we will present our recent results on the experimental observation of new topological quantum materials. These are topological superconductors and magnetic topological materials which were discovered through ARPES and timeresolved ARPES measurements with further support from firstprinciples calculations. 
Thursday, March 5, 2020 4:54PM  5:06PM 
U64.00009: Anomalous quantum oscillations in a spin3/2 topological semimetal: I. Experiment Hyunsoo Kim, Junhyun Lee, Halyna Hodovanets, Kefeng Wang, Jay Sau, Johnpierre Paglione Gapless spin3/2 quasiparticles lead to an unprecedented class of highspin topological superconductivity which hosts a Majorana fluid on the surface. The spin3/2 Fermi surface can be realized in a crystal lattice with high symmetry. The RPtBi (R=rare earth) halfHeuslers are a family of promising candidates, in which strong spinorbit interaction inverts the Bi porbital derived bands and Bi sorbital derived bands. In this particular case, the low energy quasiparticles are adequately described by the fourband Luttinger–Kohn model. In this talk, we report compelling evidence for a spin3/2 Fermi surface in YPtBi via studies of the angledependent Shubnikovde Haas (SdH) effect uniquely explained by the anisotropic effect of Zeeman interaction on spin3/2 quasiparticles, confirming the longawaited highspin nature of topological semimetal RPtBi compounds. 
Thursday, March 5, 2020 5:06PM  5:18PM 
U64.00010: Anomalous quantum oscillations in a spin3/2 topological semimetal: II. Theory Junhyun Lee, Hyunsoo Kim, Halyna Hodovanets, Kefeng Wang, Jay Sau, Johnpierre Paglione Gapless spin3/2 quasiparticles lead to an unprecedented class of highspin topological superconductivity which hosts a Majorana fluid on the surface. The spin3/2 Fermi surface can be realized in a crystal lattice with high symmetry. The RPtBi (R=rare earth) halfHeuslers are a family of promising candidates, in which strong spinorbit interaction inverts the Bi porbital derived bands and Bi sorbital derived bands. In this particular case, the low energy quasiparticles are adequately described by the fourband Luttinger–Kohn model. In this talk, we report compelling evidence for a spin3/2 Fermi surface in YPtBi via studies of the angledependent Shubnikovde Haas (SdH) effect uniquely explained by the anisotropic effect of Zeeman interaction on spin3/2 quasiparticles, confirming the longawaited highspin nature of topological semimetal RPtBi compounds. 

U64.00011: Correspondence between winding numbers and skin modes in nonhermitian systems Kai Zhang, Zhesen Yang, Chen Fang We establish exact relations between the winding of “energy” (eigenvalue of Hamiltonian) on the complex plane as momentum traverses the Brillouin zone with periodic boundary condition, and the presence of “skin modes” with open boundary condition in nonhermitian systems. This correspondence is exactly related to by our new understanding of generalized Brillouin zone, which is the curve defined on the complex plane and always surrounding the same number of zeros and poles of characteristic equation of the system. We show that the nonzero winding with respect to any complex reference energy leads to the presence of skin modes, and vice versa. We also show that both the nonzero winding and the presence of skin modes share the common physical origin that is the nonvanishing current through the system. 
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