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 R45: Topological Insulators: ExperimentLive
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Hee Taek Yi, Rutgers, The State University of New Jersey |
Thursday, March 18, 2021 8:00AM - 8:12AM Live |
R45.00001: Tuning the band structure of monolayer WTe2 using back-gating in STM Yulia Maximenko, Yueqing Chang, Mark Hirsbrunner, Taylor L Hughes, Lucas Wagner, Vidya Madhavan Two-dimensional (2D) transition metal dichalcogenides are exciting systems potentially realizing toplogically protected edge states, topological superconductivity, and strong electron correlation physics. Monolayer 1T'-WTe2 has been demonstrated to be a time-reversal-invariant 2D topological insulator that becomes a superconductor upon doping. Atomically-resolved scanning tunneling microscopy (STM) confirmed clear edge states on WTe2 monolayer islands. Here, we report an STM study of back-gated monolayer 1T'-WTe2. Along with topographical images, we present scanning tunneling spectroscopy of monolayer islands, performed while tuning the out-of-plane electric field and carrier concentration. The monolayer band structure and the edge states evolve in response to doping and back-gating. We use first principle calculations to explain the observed effects. |
Thursday, March 18, 2021 8:12AM - 8:24AM Live |
R45.00002: Terahertz conduction of SmB6 thin films and superconducting SmB6/YB6 heterostructures Jonathan Stensberg, Xingyue Han, Seunghun Lee, Johnpierre Paglione, Ichiro Takeuchi, Liang Wu Following a 2010 prediction that the anomalous low-temperature conduction in the Kondo insulator SmB6 is due to a topological surface state, making SmB6 the first topological Kondo insulator, a flurry of experimental efforts have produced promising but often inconsistent or contradictory characterizations. While a number of recent studies have attempted to harmonize these results, many experimental discrepancies remain unresolved. Here, we investigate via time domain terahertz spectroscopy the AC conduction of SmB6 thin films and heterostructures of SmB6 and the superconductor YB6. The conduction of SmB6 thin films is found to be accurately described by a two-channel model of surface and bulk states while the heterostucture conduction concords with the Mattis-Bardeen formalism of BCS superconductivity. These results support the existence of surface conducting states in SmB6 susceptible to the superconducting proximity effect. |
Thursday, March 18, 2021 8:24AM - 8:36AM Live |
R45.00003: Helical spin texture of Bi doped PbSb2Te4 topological insulator Yuya Hattori, Yuki Tokumoto, Keisuke Sagisaka, Keiichi Edagawa For the study of topological insulator (TI), scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) are powerful tools to characterize the surface electronic properties. In the case of Bi2Te3 TI, a unique quasiparticle interference (QPI) pattern observed by STM revealed severe deformation of a Dirac cone. In search of the non-deformed ideal Dirac cone, Pb-based TIs were discovered. Pb-based TIs belong to peculiar topological class (1;111) whereas traditional TIs such as Bi2Te3 belong to (1;000). PbSb2Te4 is one of the Pb-based TIs, whose Fermi energy lies in the valence band. Therefore, its surface states are difficult to be observed by ARPES measurements. |
Thursday, March 18, 2021 8:36AM - 8:48AM Live |
R45.00004: Gate field effects on the topological insulator BiSbTeSe2 interface Shuanglong Liu, Yang Xu, Yun-Peng Wang, Yong Chen, James Nathan Fry, Hai-Ping Cheng Inspired by experimental efforts, we study interfacial processes between two slabs of BiSbTeSe2 (BSTS) via first-principles calculations. Topological surface states are absent for the BSTS interface at its equilibrium separation, but our calculations show that they appear if the inter-slab distance is greater than 6 Å. More importantly, we find that topological interface states can be preserved by inserting two or more layers of hexagonal boron nitride between the two BSTS slabs. Using a first-principles based method that allows us to simulate a back gate, we observe that at low bias the extra charge induced by a gate voltage resides on the surface that is closest to the gate electrode, leaving the interface almost undoped. This explains the origin of the observed insensitivity of transport properties to back voltage at low bias. Our study resolves a few questions raised in experiments, which does not yet offer a clear correlation between microscopic physics and transport data. |
Thursday, March 18, 2021 8:48AM - 9:00AM Live |
R45.00005: Modulation of surface states in Sb2Te3/Bi2Te3 topological insulator heterostructures Vanda Mota Pereira, Chi-Nan Wu, Liu Tjeng, Simone Altendorf The direct access of the topological surface states by electrical transport measurements is a necessary requirement for the implementation of the exceptional properties of topological insulators (TIs) in applications. In most TIs, however, the bulk is not insulating and the Dirac point is not exposed or not close to the Fermi level, masking the topological phenomena. Therefore, band structure engineering, e.g. by combining TI materials with complementary electronic properties, is in the focus of the research. Here we study the very promising approach of interfacing two TIs, namely Bi2Te3 and Sb2Te3. Heterostructures of Bi2Te3 thin films [1-3] with various thicknesses of the Sb2Te3 top layer are prepared by molecular beam epitaxy. Using in situ angle-resolved photoelectron spectroscopy, we are able to differentiate the modulation of the surface states from the shift of the chemical potential due to doping. Moreover, the interdiffusion at the interface of the TIs is studied and optimized by utilizing growth recipes involving different growth temperatures. |
Thursday, March 18, 2021 9:00AM - 9:12AM Live |
R45.00006: Comparative Study of MBE Grown Epitaxial Bi2Te3 On Various Standard Substrates Archit Bhardwaj, Dhavala Suri, Karthik Raman Three dimensional topological insulators (TIs) are materials in which the bulk insulating gap is bridged by highly conducting surface states that are topologically protected [1]. A systematic growth of these materials is a crucial step to investigate fundamental quantum properties in pristine films and for further hetero-structure designs in exploring proximity driven effects [2]. Here, we show high quality epitaxial growth of Bi2Te3 on a variety of substrates (sapphire, STO, GaAs and SiO2) and thereby compare the crucial parameters in terms of film quality such as mobility, carrier concentration etc. The films are analysed by in-situ RHEED, ex-situ XRD, Raman and rigorous electron transport measurements. The growth conditions are optimized to portray surface state dominant characteristics in each sample, observed via weak anti-localization effects; and hence catering to the demands of different substrates for a variety of applications. Magnetic field dependent transport measurements at low temperature exhibit interesting anisotropic effects in the in-plane field configuration, which will be discussed. |
Thursday, March 18, 2021 9:12AM - 9:24AM Live |
R45.00007: Observation of symmetry-protected zero modes in topolectrical circuits Huanhuan Yang, Zhixiong Li, Yuanyuan Liu, Yunshan Cao, Peng Yan Higher-order topological insulators are a new class of topological phases of matter, originally conceived for electrons in solids. It has been suggested that the ZN Berry phase (Berry phase quantized into 2π/N) is a useful tool to characterize the symmetry-protected topological states, whereas the experimental evidence is still elusive. Recently, topolectrical circuits have emerged as a simple yet very powerful platform for studying topological physics that are challenging to realize in condensed-matter systems. Here, we present an experimental observation of second-order corner states characterized by the Z3 Berry phase in topolectrical circuits. We demonstrate theoretically and experimentally that the localized second-order topological states are protected by a generalized chiral symmetry of tripartite lattices, and they are pinned to “zero energy.” By introducing extra capacitors within sublattices in the circuit, we are able to examine the robustness of the zero modes against both chiral-symmetry-conserving and breaking disturbances. Our work paves the way for testing exotic topological band theory by electrical-circuit experiments. |
Thursday, March 18, 2021 9:24AM - 9:36AM Live |
R45.00008: Observation of Flat Frequency Bands at Open Edges and Antiphase Boundary Seams in Topological Mechanical Metamaterials Kai Qian, Linghua Zhu, Keun Hyuk Ahn, Camelia Prodan In this talk, we report the observation of the flat frequency bands of the topological origin at open edges and antiphase boundary seams in mechanical metamaterials [1], as predicted by the recent theoretical studies on a two-dimensional chiral Hamiltonian [2]. It is experimentally and computationally demonstrated that topological flat bands can occur at open edges of planar systems and antiphase boundary seams of ring or tubular systems. We also show that the flatness of the edge bands and the size of the localized states can be controlled by the distance between open edges, and compare with the theory. This study suggests that similar flat bands could occur in other metamaterials, such as photonic crystals and electronic metamaterials. |
Thursday, March 18, 2021 9:36AM - 9:48AM Live |
R45.00009: Pb-doped p-type Bi2Se3 thin films via interfacial engineering Jisoo Moon, Zengle Huang, Weida Wu, Seongshik Oh Due to high density of native defects, the topological insulator (TI), Bi2Se3, is naturally n-type. Although Bi2Se3 can be converted into p-type by substituting 2+ ions for Bi, only light elements such as Ca have been so far effective as the compensation dopant. Considering that strong spin-orbit coupling (SOC) is essential for the topological surface states, a light element is undesirable as a dopant, because it weakens the strength of SOC. In this sense, Pb, the heaviest 2+ ion located right next to Bi in the periodic table, is the most ideal p-type dopant for Bi2Se3. However, Pb-doping has not achieved p-type Bi2Se3 both in thin films and bulk crystals. Here, by utilizing an interface engineering, we achieved the first Pb-doped p-type Bi2Se3 thin films. Furthermore, at heavy Pb-doping, the mobility is substantially higher than that of Ca-doped samples, indicating that Pb is a less disruptive dopant than Ca. With this SOC-preserving counter-doping, it is now possible to fabricate Bi2Se3 with tunable Fermi levels without compromising their topological properties. [1] |
Thursday, March 18, 2021 9:48AM - 10:00AM Live |
R45.00010: Z-dependent spin-momentum locking in monolayer 1T’-WTe2 Yulia Maximenko, Yueqing Chang, Guannan Chen, Mark Hirsbrunner, Waclaw Swiech, Taylor L Hughes, Lucas Wagner, Vidya Madhavan Monolayer 1T’-WTe2 is a quantum spin Hall insulator with a well-defined bulk gap and helical edge states. It has been predicted to undergo a topological phase transition upon breaking the inversion symmetry with gating [1]. Recent scanning tunneling microscopy (STM) experiments by Maximenko et. al. have found a surprising linear dependence of the gap on gating voltage. We present computational results of the electronic structure of monolayer 1T’-WTe2 with the effect of gating, using a tight-binding model derived from the Wannierised Kohn-Sham orbitals computed from density functional theory. We find that the top and bottom surfaces of the monolayer 1T’-WTe2 exhibit opposite spin-momentum locking properties. This effect causes the STM measured gap to show a linear response upon gating. |
Thursday, March 18, 2021 10:00AM - 10:12AM Live |
R45.00011: Electronic structure of a weak topological insulator RhBi2 Kyungchan Lee, Gunnar F Lange, Lin-Lin Wang, Brinda Kuthanazhi, Thais Victa Trevisan, Na Hyun Jo, Benjamin Schrunk, Peter Orth, Robert-Jan Slager, Paul C Canfield, Adam Kaminski We report a study of electronic structure of triclinic RhBi2 using laser based angle resolved photoemission spectroscopy (ARPES), DFT calculations, and effective model. We observe two surface Dirac points demonstrating that RhBi2 displays topological surface states (TSS) arising from WTI phase at (100) surface. Our results reveal TSS with saddle points that are located in the vicinity of a Dirac point resulting in a van Hove singularity close to the Fermi energy. Due to the combination of exotic features, this material offers great potential as a material platform for novel quantum effects. |
Thursday, March 18, 2021 10:12AM - 10:24AM Live |
R45.00012: Signatures of Higher Order Topology in S-Bi-S Junctions Alexandre Bernard, Alik Kasumov, Richard Deblock, Yang Peng, Yuval Oreg, Felix von Oppen, Helene Bouchiat, Sophie Gueron Perfect 3D pure bismuth is a very intriguing material, but its electronic states were considered topologically trivial until recent works suggesting that it may host 1D helical states on some hinges. Indeed, bismuth fits in the new class of material called "second order topological insulator" (SOTI). |
Thursday, March 18, 2021 10:24AM - 10:36AM Live |
R45.00013: Influence of post-deposition annealing on the transport properties of sputtered Bi2Se3 thin films Yub Raj Sapkota, Dipanjan Mazumdar In the past decade, Bi2Se3 has been one of the most investigated TI materials. The physical properties of Bi2Se3 are dictated by selenium vacancies irrespective of the growth method. Controlling the number of vacancies is a challenging problem, but it can be influenced by factors such as substrate and growth temperature. In this work, we demonstrate that post-deposition annealing temperature is also effective in controlling the carrier concentration of Bi2Se3 thin films. Ultra-thin Bi2Se3 films were fabricated on quartz substrates using magnetron sputtering at room temperature, and their resistivity, bulk carrier concentration, and bulk mobility are measured as a function of post-deposition annealing temperature under vacuum conditions ranging from 180 – 350 °C. We find that carrier concentration can vary by an order of magnitude, and we obtained values as low as ~1x1019 cm-3 between 200-250 °C which compares very well with some of the best literature reports on films made by MBE. Overall, our work demonstrates that the transport properties of Bi2Se3 films are highly tunable through post-annealing temperature, which may be of interest in applied areas such as nanoelectronics and spintronics. |
Thursday, March 18, 2021 10:36AM - 10:48AM Live |
R45.00014: Gate-tunable spin galvanic effect in topological insulator–graphene heterostructures Dmitrii Khokhriakov, Saroj Dash Unique electronic spin textures in topological states of matter are promising for emerging spintronic technologies (Nano Letters 15, 12, 7976 (2015), Phys. Rev. B 97, 125414 (2018)). Here we integrate topological insulator (TI) in van der Waals heterostructures with graphene to engineer proximity-induced spin-orbit coupling (Science Advances, 4, 9, eaat9349 (2018)) and charge-spin conversion (Nature Communication 11, 3657 (2020)) phenomena. In these heterostructures, we experimentally demonstrate a gate-tunable Rashba-Edelstein effect at room temperature, allowing for efficient conversion of a non-equilibrium spin polarization into a transverse charge current (Nature Communication 11, 3657 (2020)). Importantly, using a gate voltage, we reveal a strong electric field tunability of both amplitude and sign of the spin-galvanic signal. These findings provide an efficient route for realizing all-electrical and gate-tunable spin signals using TIs and graphene in heterostructures. |
Thursday, March 18, 2021 10:48AM - 11:00AM Not Participating |
R45.00015: Thermal and electrical transport behavior of topological insulator ZrTe5 Junbo Zhu, Changmin Lee, Takehito Suzuki, Shiang Fang, Nuh Gedik, Joseph Checkelsky We report a study of electric, thermoelectric, thermodynamic measurements and angle resolved photoemission spectroscopy (ARPES) of single crystals of topological insulator candidate ZrTe5 grown by both chemical vapor transport and flux method. The transport response is characteristic of a small gap semiconductor with band parameters consistent with those observed by ARPES. The thermoelectric response shows a significant enhancement in magnetic field and unconventional behavior in the quantum limit. We discuss the possible mechanisms underlying these observations in the context of the band properties deduced from our probes of fermiology. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700