Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E01: Electronic Structures of Weyl Semimetals and Topological Insulators 
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Sponsoring Units: DCMP Chair: Andrew Weber, Donostia International Physics Center Room: BCEC 106 
Tuesday, March 5, 2019 8:00AM  8:12AM 
E01.00001: Evolution of the Electronic Structure of MoTe2 under Pressure Yajian Hu, Yuk Tai Chan, Kwing To Lai, Kin On Ho, Xiaoyu Guo, King Yau Yip, Swee Kuan Goh, Yuji Aoki, Tatsuma D. Matsuda Transition metal dichalcogenides have recently been heavily studied owing to their intriguing physical properties such as extremely large magnetoresistance (MR) in WTe_{2} and MoTe_{2}. Further interests are attracted when they are predicted as candidates of typeII Weyl semimetals. Moreover, as both WTe_{2} and MoTe_{2} host superconductivity, this opens up the possibility of topological superconductivity. 
Tuesday, March 5, 2019 8:12AM  8:24AM 
E01.00002: Crystal structure and electronic structure of noncentrosymmetrical trigonal PtBi_{2} Wenxiang Jiang, Fengfeng Zhu, Ping Li, Haiyang Ma, Haohua Sun, Zhongqiang Yang, Canhua Liu, Dandan Guan, Jinfeng Jia, Weidong Luo, Dong Qian Electronic structure of single crystalline γPtBi2 is studied by angleresolved photoemission spectroscopy(ARPES). It is proposed by theoretical calculation that the stable structure of γPtBi2 should be noncentrosymmetric. ARPES measurement gives powerful evidences in this paper that different band structures between two types of cleaved surface are clearly observed. Bulk and surface bands are characterized through systematically photon dependent measurement. The bulk band dispersions agree well with the firstprinciple calculation except Rashba shaped surface states. The topography studied by STM also confirms the existence of two different cleaved surfaces. Besides, some efforts has been made to demonstrate the existence of triply degenerate point fermions. 
Tuesday, March 5, 2019 8:24AM  8:36AM 
E01.00003: SpinResolved Electronic Response to the Phase Transition in MoTe_{2} Andrew Weber, Philipp Rüßmann, Nan Xu, Stefan Muff, Mauro Fanciulli, Arnaud Magrez, Philippe Bugnon, Helmuth Berger, Nicholas C Plumb, Ming Shi, Stefan Bluegel, Phivos Mavropoulos, J. Hugo Dil The Weyl semimetal MoTe_{2} is studied by spin and angleresolved photoemission spectroscopy across the centrosymmetrybreaking structural transition temperature of the bulk. A threedimensional spintexture is observed in the bulk Fermi surface in the low temperature, noncentrosymmetric phase that is consistent with firstprinciples calculations. The spin texture and two types of surface Fermi arc are not completely suppressed above the bulk transition temperature. The lifetimes of quasiparticles forming the Fermi arcs depend on thermal history and lengthen considerably upon cooling toward the bulk structural transition. The results indicate that a new form of polar instability exists near the surface when the bulk is largely in a centrosymmetric phase. 
Tuesday, March 5, 2019 8:36AM  8:48AM 
E01.00004: Investigation of the magnetic Weyl semimetal candidate Co_{3}Sn_{2}S_{2} by ARPES. Ilya Belopolski, Tyler Cochran, Enke Liu, YuHsin Su, Jiaxin Yin, Guoqing Chang, Songtian Sonia Zhang, Zurab Guguchia, Claudia Felser, Zahid Hasan Topological phases in magnetic materials are a topic of current interest in the community. Recently, the kagomelattice ferromagnet Co_{3}Sn_{2}S_{2} was predicted to be a Weyl semimetal, while transport showed an exceptionally large anomalous Hall angle. Motivated by these exciting results, we use synchrotron ARPES to study single crystal Co_{3}Sn_{2}S_{2}. We observe a strong photon energy dependence consistent with outofplane k_{z} dispersion, even at moderate VUV photon energies. We compare our ARPES results with DFT and find a general match, with typical disagreement of ~ 0.1 eV. To address this disagreement, we perform muon/neutron scattering on Co_{3}Sn_{2}S_{2} to better understand the magnetic state experimentally. We comment on progress using our muon/neutron results to match DFT to ARPES and evaluating possible changes in the predicted Weyl phase and other topological indices. Our results suggest that the search for topological magnets might benefit from an iterative approach building on muon/neutron measurements of the magnetic state, DFT and ARPES. 
Tuesday, March 5, 2019 8:48AM  9:00AM 
E01.00005: Surface resonances of topological origin in bcc iron Oleg Yazyev, Daniel Gosálbez Martínez, Gabriel Autès Chiral band degeneracies are ubiquitous in the band structures of systems wtih broken inversion or timereversal symmetries. While in Weyl semimetals such degeneracies are isolated near the Fermi level, the broadly defined notion of topological metal implies the presence of disconnected Fermi surface sheets characterized by nonzero Chern numbers. Bcc iron is an archetypal example of ferromagnetic metal with two nontrivial Fermi surface electron pockets along the direction parallel to the magnetization [1]. In this work, we investigate the surfacestate signatures of the topological nature of these Fermi surface pockets. We find that the (110) surface presents arclike resonances attached to the nontrivial electron pockets. These Fermi arc resonances are due to two chiral degeneracies, a typeI elementary Weyl point and a typeII composite (Chern number ±2) Weyl point, located at slightly different energies. We further show that such surface resonances can be controlled by the orientation of magnetization, and can eventually be eliminated following a topological phase transition. 
Tuesday, March 5, 2019 9:00AM  9:12AM 
E01.00006: Sharp Orientationdependent Quantum Oscillations in HoPtBi Connor Roncaioli, Prathum Saraf, Yun Suk Eo, Hyunsoo Kim, Johnpierre Paglione Rareearth platinum and palladiumbismuthides have been host to rich phenomenon in the search for topological states and Weyl semimetals. YPtBi in particular is host to a spinsplit fermi surface which hosts a spin3/2 superconducting state. In this study we expand this investigation to HoPtBi, a magnetic analog to YPtBi with an AFM ground state and a paramagnetic state above 1.2K. We present orientationdependent measurements of quantum oscillations in HoPtBi and find a strong orientation dependence near the crystallographic [110] direction very similar to, but phenomenologically distinct from the behavior of YPtBi. 
Tuesday, March 5, 2019 9:12AM  9:24AM 
E01.00007: Observation of surface Dirac dispersion in transition metal dipnictides Gyanendra Dhakal, Md Mofazzel Hosen, WeiChi Chiu, Bahadur Singh, Klauss Dimitri, Baokai Wang, Firoza Kabir, Christopher Sims, Sabin Regmi, Hsin Lin, Dariusz Kaczorowski, Arun Bansil, Madhab Neupane The experimental discovery of Dirac and Weyl Fermions, quasiparticles existing in low energy excitation in condensed matter physics, has paved a new avenue of research interests in condensed matter physics. Recently, the Lorentzinvariance breaking Weyl semimetallic state has been reported in MoP_{2} and WP_{2}. Arsenic counterparts of these compounds, which also harbor high magnetoresistance, demand the detailed study to investigate the possible semimetallic state possessed by them. Here, we discuss our angleresolved photoemission spectroscopy (ARPES) and firstprinciples calculations results on the electronic structures of MoAs_{2} and WAs_{2}, which reveal the presence of a surface Dirac cone. Our systematic electronic structures analysis reveals the termination dependent electronic structure in these compounds. Our study offers the opportunity to study the various quantum phase transitions within this family. 
Tuesday, March 5, 2019 9:24AM  9:36AM 
E01.00008: ARPES measurements on Dirac nodalline semimetal candidate TiRhAs Hang Li, Dayu Yan, Congcong Le, Binbin Fu, Youguo Shi, Hong Ding, Tian Qian

Tuesday, March 5, 2019 9:36AM  9:48AM 
E01.00009: Observation of Yamaji Magic Angles in Bismuth Nanowires Tito Huber, Albina Nikolaeva, Leonid Konopko Experimental studies that probe the surface of bulk bismuth as a composite of topological insulator edges and hinges on the surface of bulk Bi are lacking. We present angledependent transverse magnetoresistance (TMR) oscillation measurements of small diameter ( 50 nm ) bismuth nanowires where electronic transport is dominated by the surface, rather than the bulk in the core of the nanowire, because of quantum confinement. We find that the TMR of the surface states in our nanowires exhibits peaks for a sequence of nanowire rotation angles that strongly suggest an interpretation in terms of Yamaji magic angles. Magic angles are observed in layered and other lowdimensional conductors with weak interplanar coupling that are amenable to be described by an open, corrugated, Fermi surface. In contrast to surface states, bulk bismuth does not display magic angles since the Fermi surface is closed. We will discuss our interpretation of surface states of bismuth and the main Fermi surface parameters that we observe: orientation of the Fermi surface, Fermi wavevector, and coupling strength. 
Tuesday, March 5, 2019 9:48AM  10:00AM 
E01.00010: Topological LineLike Bound States in the Continuum Manabu Takeichi, Shuichi Murakami Bound states in the continuum (BIC) have been studied mainly in optics. Recently, electronic BIC have been proposed. They appear as points in the momentum space and are protected topologically by the Chern number. In this study, we propose a new type of BIC protected by the winding number, which is one of the topological invariants. These BIC appear as lines in the momentum space, and are realized in a multilayer model consisting of honeycomblattice layers. We show band structure and spatial localization of the BIC in this model. The wavenumbers at which the BIC appear can be explained in terms of topology in the momentum space. 
Tuesday, March 5, 2019 10:00AM  10:12AM 
E01.00011: Scanning tunneling spectroscopy studies of the topological states in the Dirac metal Hf_{2}Te_{2}P Timothy Boyle, Antonio Rossi, Peter Carlson, Moira K Miller, Jingtai Zhao, Morgan Walker, Valentin Taufour, Inna Vishik, Eduardo H Da Silva Neto Recent angleresolved photoemission spectroscopy experiments and theoretical calculations indicate the existence of multiple Dirac states in the topological material Hf_{2}Te_{2}P [1]. In this study we use scanning tunneling spectroscopy (STS) to measure the electronic band structure of the material. Using STS as a direct probe of the realspace local density of states, we identify quasiparticle interference patterns that allow us to measure the topological surface states. The results will be discussed in the context of density functional theory calculations that predict multiple topological states below and above the Fermi energy. 
Tuesday, March 5, 2019 10:12AM  10:24AM 
E01.00012: A Consistent View of the Samarium Hexaboride Surface Terminations Hannes Herrmann, Peter Hlawenka, Konrad Siemensmeyer, Eugen Weschke, Natalya Shitsevalova, Slavomir Gabáni, Karol Flachbart, Oliver Rader, Martin Sterrer, Emile Rienks Since the establishment of topological insulators, a lot of interest has turned to finding systems that combine topology with strong electron correlations. This led Dzero et al. to propose that Kondo insulators, materials that open a band gap by mixing local and itinerant states of opposite parity, should fall into this category [1]. The effort spurred by this proposal has advanced the state of knowledge on SmB_{6}, the leading candidate for a topological Kondo insulator [2]. The question of its topology, however, remains unanswered. 
(Author Not Attending)

E01.00013: Disentangling orbital and spin characteristics of surfacederived states in Dirac nodal line semimetals XIAOXIAO WANG, Jiahua Chen, Mingtian Zheng, Shilong Wu, Kazuki Sumida, Tomoki Yoshikawa, Tatiana Menshchikova, Igor Rusinovip, Eike F Schwier, Koji Miyamoto, Munisa Nurmamat, Taichi Okuda, Kenya Shimada, Mario Novak, Evgueni Chulkov, Akio Kimura In this work, we explore surface states of nonsymmorphic semimetals with lifted band degeneracy at the symmetry points. HfSiS, a typical Dirac nodalline semimetal with the nonsymmorphic symmetry exhibits a Rashbatype spinsplit surface state. In this regard, we explore the Rashaba surface states which draw an analogy to the topological materials, where the spin and orbital entanglement takes place. We have performed spin and angleresolved photoemission spectroscopy experiment on HfSiS and ZrSiS single crystals with ppolarized and spolarized light. The observed variation in the intensity distribution upon changing the light polarization tells us that the surface states along the MXM line are mainly composed of dz^{2} orbitals, and change into d_{yz} along the GXG line. Combining the observed spin polarizations with the result of the slab calculation, we have concluded that the surface bands surrounding the X point exhibit a quite anisotropic spin and orbital texture. Our findings provide a new way of light manipulation by controlling the spin structure in materials which is important for future applications. 
Tuesday, March 5, 2019 10:36AM  10:48AM 
E01.00014: Controlling SpinPolarized Currents on the Surface of Topological Insulators Samuel Ciocys, Takahiro Morimoto, Kenneth Gotlieb, Zahid Hussain, James G. Analytis, Joel Moore, Alessandra Lanzara The appearance of topologically protected spinmomentum locked surface states with forbidden backward scattering on the surface of topological insulators gives rise to robust room temperature spin currents making them ideal candidates for the realization of spintronic devices. So far however, despite a decade of research in this field, very little is known on how to access and manipulate such currents in a manner that is accessible in chipbased devices. Here we reveal a technique to generate longlived spincurrents of arbitrary geometry with tunable magnitude and duration on the surface of Bi_{2}Se_{3} topological insulators. Timeresolved angleresolved photoemission spectroscopy, together with a quantitative model, uncovers a remarkable contrast with respect to doping thanks to the intrinsic correlation between the spinlocked surface state and an insulating bulk. This work demonstrates that localized spincurrents are accessible with long lifetimes, easily tuned in both magnitude and duration, merging photonics and spintronics based devices on the same material. 
Tuesday, March 5, 2019 10:48AM  11:00AM 
E01.00015: Interaction of coherent phonons with spinorbit coupled surface states Jonathan Sobota, Hadas Soifer, Patrick S Kirchmann, Zhixun Shen Spinpolarized electronic states form at the surface of materials due to the combination of spinorbit coupling and broken inversion symmetry. This phenomenon was first established for Shockley states at the surface of noble metals such as gold, and more recently, has been recognized as a central mechanism responsible for the formation of topologically nontrivial states. Given the fundamental significance of these states, as well as their potential role in spintronics applications, it is important to understand their interaction with collective excitations of the crystal lattice. 
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