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 F45: Electronic Structure of Topological Insulators and Interacting Topological SystemsLive
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Sponsoring Units: DCMP Chair: Victor Vakaryuk, Johns Hopkins University |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F45.00001: Topological Surface State Evolution in Chemical Etching of Bi2Se3 Ruohan Wang, Yusheng Hou, Hongtao Rong, Han Wu, Yucheng Guo, Yichen Zhang, Ruqian Wu, Jianwei Huang, Ming Yi Topological insulators are materials with insulating bulk while maintaining metallic surface states, which are protected by their topological properties against disorder. Bi2Se3 is a typical topological insulator characterized by its large bulk band gap and a robust Dirac cone topological surface state with the crossing point inside the bulk gap. Recently, it has been reported that Bi (111) bilayer can form spontaneously on top of Bi2Se3 films under surface etching, which in turn alters its electronic band structures. While the electronic structures of Bi2Se3 has been well understood both experimentally and theoretically over the past years, the transitional stages under which a pure Bi2Se3 evolves into Bi2-Bi2Se3 state still remain unclear. In this talk, the detailed band structure evolution of pristine Bi2Se3 sample under surface etching measured by ARPES will be presented, with an emphasis on the topological surface state. Density Functional Theory calculations will be discussed to provide insights into the topological nature of the intermediate stages during the etching process of this material. |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F45.00002: Ab initio study of surface states in Bi4Te3 Omar Ashour, Steven G Louie, Zhenglu Li The crystal structure of the layered material Bi4Te3, a member of the adaptive series of crystals (Bi2)m(Bi2Te3)n, forms a superlattice of alternating Bi2 and Bi2Te3 layers. Recent experimental results indicate the presence of unusual surface states in this material and our calculations show that Bi4Te3 possesses topological surface states. In this work, we perform ab initio density functional theory calculations of bulk and slab geometries to further investigate the surface states of Bi4Te3. We additionally study the effects of charge transfer at the surface using tight binding calculations. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F45.00003: Dirac electronic states of Bi2Se3 thin films on ferromagnetic Cr2Si2Te6 studied by high-resolution ARPES Takemi Kato, Katsuaki Sugawara, Naohiro Ito, Kunihiko Yamauchi, Takumi Sato, Tamio Oguchi, Takashi Takahashi, Yuki Shiomi, Eiji Saitoh, Takafumi Sato We have epitaxially fabricated Bi2Se3 thin films on van der Waals ferromagnet, Cr2Si2Te6 (CST), and investigated their electronic structure by high-resolution angle-resolved photoemission spectroscopy (ARPES) [1]. We observed a large energy gap at the Dirac point in 2 quintuple-layer (QL) Bi2Se3 on CST in contrast to the gapless Dirac-cone state in 6 QL Bi2Se3 on CST. Compared to 2 QL Bi2Se3 on Si substrate, we found that the Dirac point of 2 QL Bi2Se3 on CST is located at lower binding energy with enhanced gap magnitude. In this talk, we will show temperature dependence of band structure across TC of CST, and discuss the origin of modulation of Dirac electronic states in Bi2Se3/CST heterostructure in terms of the lattice strain effect, interfacial coupling, and magnetic proximity effect. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F45.00004: Absence of equilibrium edge currents in theoretical models of topological insulators Wei Chen The low-energy sector of 2D and 3D topological insulators (TIs) exhibits propagating edge states, which has speculated the existence of equilibrium edge currents or edge spin currents. We demonstrate that if the low-energy sector of TIs is regularized in a straightforward manner into a square or cubic lattice, then the current from the edge states is in fact canceled out exactly by that from the valence bands, rendering no edge current [1]. This result serves as a warning that for any equilibrium property of topological insulators, the contribution from the valence bands should not be overlooked. In these regularized lattice models, there is a finite edge current only if the Dirac point of the edge states is shifted away from the chemical potential, for instance, by doping, impurities, edge-confining potential, surface band bending, or gate voltage. The edge current in small quantum dots as a function of the gate voltage is quantized, and the edge current can flow out of the gated region up to the decay length of the edge state. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F45.00005: Temperature-dependent electronic structure in a higher order topological insulator candidate EuIn2As2 Sabin Regmi, Md Mofazzel Hosen, Barun Ghosh, Bahadur Singh, Gyanendra Dhakal, Christopher Sims, Baokai Wang, Firoza Kabir, Klauss Dimitri, Yangyang Liu, Amit Agarwal, Hsin Lin, Dariusz Kaczorowski, Arun Bansil, Madhab Neupane Higher order topological insulator (HOTI) is a novel quantum topological phase with gapless states along the hinges of a crystal. Despite theoretical predictions in several potential materials, enough experimental studies on crystalline HOTI materials is still lacking. The interplay of magnetism and topology has been shown to give rise to various magnetic topological states, including axion insulator and HOTI states. In this talk, we will present a systematic study on the electronic structure of EuIn2As2 and its evolution across the antiferromagnetic transition below 16 K by utilizing high-resolution angle-resolved photoemission spectroscopy combined with parallel first-principles computation. The antiferromagnetic EuIn2As2 has been predicted to host both the axion and the HOTI states. We directly observe the linearly dispersing hole-like bands crossing the Fermi level and the change in their dispersion across the magnetic phase transition. Our study points to EuIn2As2 as being a promising material to explore interplay between topology and magnetism. |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F45.00006: Temperature-Induced Topological Phase Transition in Quasi-One-Dimensional Material Bi4I4 Jianwei Huang, Sheng Li, Ji Seop Oh, Han Wu, Xiaoyuan Liu, Yucheng Guo, Yichen Zhang, Makoto Hashimoto, Donghui Lu, Jonathan Denlinger, Robert J Birgeneau, Fan Zhang, Bing Lv, Ming Yi Quasi-one-dimensional materials provide a fascinating platform for studying diverse topological phases as well as related topological phase transitions. Bi4I4 is a quasi-one-dimension material with two different stacking sequences of the same building block along the c-axis, which results in two different structures – alpha-Bi4I4 and beta-Bi4I4. The two different phases are predicted to possess different topological properties including higher order hinge modes and can be tuned by temperature. Due to its quasi-one-dimensional nature, it can be cleaved along different surfaces hence be examined for strong versus weak topological insulator properties. In this talk, temperature dependent ARPES experimental results on different surfaces of Bi4I4 across the structural transition will be presented. Topological nature on different surfaces will be discussed for the alpha- and beta-Bi4I4 to elucidate the topological phase transition in this material system. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F45.00007: 2D Fermi surface and topological states in the CDW compound TaTe4 Pedro Henrique Gonçalves, Maximilian Thees, Rosa Luca Bouwmeester, Emma David, Emmanouil Frantzeskakis, Franck Fortuna, Patrick Le Fèvre, Rogério Magalhães-Paniago, Paula Giraldo-Gallo, Andrés Santander-Syro Transition metal chalcogenides have attracted considerable attention of the scientific community during the last few years, exhibiting remarkable effects such as topological non-trivial states and induced superconductivity. TaTe4 is a quasi-1D tetrachalcogenide that presents a CDW instability caused by a periodic lattice distortion, forming a commensurately modulated structure stable in a wide temperature range. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F45.00008: Spin-polarized tunable photocurrents Matias Berdakin, Esteban A. Rodriguez-Mena, Luis E. F. Foa Torres Circular dichroism, a distinctively different response to left and right-handed circularly polarized light, is an example of a phenomenon involving light-matter interaction that has been heavily exploited to control valley polarization in two-dimensional materials. In most studies, light-matter interaction enters perturbatively and does not modify the electronic properties. But beyond this weak-coupling regime, Floquet-engineering has shown that we can use light to change the band-structure of a material and even its topology, generating a Hall response. |
Tuesday, March 16, 2021 1:06PM - 1:18PM Not Participating |
F45.00009: Probing the gap of single layer WTe2 by tunnel capacitance spectroscopy Evan Zalys-Geller, Sergio de la Barrera, Xirui Wang, Kenji Yasuda, Pablo Jarillo-Herrero, Raymond Ashoori Single layer WTe2 displays a topological insulator state in addition to unexpected superconductivity and possible correlated effects at low temperatures. While early theoretical efforts predicted a trend towards gap formation due to spin-orbit coupling, surprising new experimental results suggest a potential many-body origin for the insulating gap observed in transport and spectroscopic measurements. While transport measurements only provide limited information about the density of states, tunnel capacitance spectroscopy provides detailed information about both thermodynamic and single particle properties of all electronic states, including those in the insulating gap. To further elucidate the origins of this gap, we probe these thermodynamic properties and spectroscopic signatures of the gap of WTe2 embedded in a vertical tunneling geometry with capacitive sensing. |
Tuesday, March 16, 2021 1:18PM - 1:30PM Live |
F45.00010: Observation of Dirac Band Splitting in a Peierls Semimetal (TaSe4)2I Hemian Yi, Lujin Min, Zengle Huang, Rui Wu, Ruoxi Zhang, Yifan Zhao, Ling-Jie Zhou, Moses H W Chan, Weiwei Xie, Weida Wu, Zhiqiang Mao, Zhijun Wang, Cui-Zu Chang (TaSe4)2I shows a characteristic metal-insulator phase transition by decreasing temperature. Above the charge density wave (CDW) temperature Tc, (TaSe4)2I has been predicted to be a Weyl semimetal phase. Below Tc, it becomes an axion insulator phase. Here, we performed the angle-resolved photoemission spectroscopy (ARPES) measurements on the (110) surface of (TaSe4)2I and observed two sets of Dirac-cone-shaped bands. Our first-principles calculations show that each Dirac band is composed of two overlapped Weyl bands. Moreover, we found that each Dirac band exhibits tens of meV energy splitting. By the combination of our theoretical calculations and core level measurements, we demonstrated that the Dirac band splitting is a result of the loss of the iodine anion on the cleaved (110) surface. Our ARPES results further show that the iodine loss-induced Dirac band splitting can be altered by temperature. Our findings shed light on the interplay between band topology and CDW order in a Peierls semimetal and will motivate more studies on these strongly correlated topological condensed matter systems. |
Tuesday, March 16, 2021 1:30PM - 1:42PM Live |
F45.00011: Saddle-point Van Hove singularity in the topological surface states of Pt2HgSe3 Barun Ghosh, Sougata Mardanya, Bahadur Singh, XIAOTING ZHOU, Baokai Wang, Tay-Rong Chang, Chenliang Su, Hsin Lin, Amit Agarwal, Arun Bansil Saddle-point Van Hove singularities in the topological surface states are interesting because they can provide a new pathway for accessing exotic correlated phenomena in topological materials. Here, based on first-principles calculations combined with a kp model Hamiltonian analysis, we show that the layered platinum mineral jacutingaite (Pt2HgSe3) harbors saddlelike topological surface states with associated Van Hove singularities [1]. Pt2HgSe3 is shown to host two distinct types of nodal lines without spin-orbit coupling (SOC), which are protected by combined inversion (I) and time-reversal (T ) symmetries. Switching on the SOC gaps out the nodal lines and drives the system into a topological state with nonzero weak topological invariant Z2 = (0; 001) and mirror Chern number nM = −2. Surface states on the naturally cleaved (001) surface are found to be nontrivial with a unique saddle-like energy dispersion with type II Van Hove singularities. Our results indicate that Pt2HgSe3 is an ideal candidate material for exploring the properties of topological insulators with saddle-like surface states. |
Tuesday, March 16, 2021 1:42PM - 1:54PM Live |
F45.00012: Fermi Surface of Frustrated Kagome Metal CoSn Kaya Wei, Jorge Galeano Cabral, Oladehin Olatunde, Eliana Karr, David E Graf, Ryan Baumbach, Theo Siegrist Very recently, topological flat bands in frustrated kagome metal CoSn were observed using angle-resolved photoemission spectroscopy and band structure calculations. [1] Using the molten flux method, we have successfully synthesized large single crystals of CoSn. After detailed structural characterizations, we performed magnetoresistance and torque magnetometry measurements in magnetic fields up to 35 T. Clear quantum oscillations were observed and analyzed in order to map the Fermi surface. In this talk we will discuss detailed results of the Fermi surface topology measurements and prospects for tuning the Fermi level. |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F45.00013: Observation of a topological drumhead surface state in a topological semimetal Ryo Mori, Kefeng Wang, Takahiro Morimoto, Jonathan Denlinger, Johnpierre Paglione, Alessandra Lanzara Topological non-trivial states of matter manifest unique electronic structures, including 3D Dirac line nodes and topological surface states. One notable topological surface states, drumhead surface states, have received significant attention because of its unique flat dispersion. Despite a large number of works, such a flat signature of drumhead states remains elusive. We will present the experimental evidence of nearly-flat drumhead surface states in a topological semimetal BaAl4 using angle-resolved photoemission spectroscopy and discuss these results in terms of correlations. |
Tuesday, March 16, 2021 2:06PM - 2:18PM On Demand |
F45.00014: Observation of optical absorption correlated with surface state of topological insulator Jiwon Jeon, Eunjip Choi We performed broadband optical transmission measurements of Bi2Se3 and In-doped (Bi1−xInx )2Se3 thin |
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