Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V02: Topological Materials -- Mesoscopic and Novel ProbesFocus
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Sponsoring Units: DMP Chair: Valla Fatemi, Yale Univ Room: BCEC 107A |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V02.00001: Pressure Induced Fermi Surface in Sb2Se3 Uma Garg, Nathaniel Smith, William Christopher Rexhausen, Audrey Grockowiak, Alexey Suslov, Stanley W Tozer, Prasenjit Guptasarma Studies of a new class of Topological Insulators, believed to be a new quantum phase of matter with a 2-dimensional Fermi surface, have led to a search for other insulators or semi-metals in which topologically non-trivial properties can be tuned using a chemical, structural, or external thermodynamic parameter. Here, we report studies of Shubnikov-de Haas oscillations as a function of pressure and magnetic field orientation on single crystals of antimony selenide (Sb2Se3). Sb2Se3 is a band insulator with a 1 eV bandgap under ambient conditions; it is metallic above 3 GPa, and superconducting above 10 GPa. Our Sb2Se3 single crystals are orthorhombic, unlike rhombohedral Bi2Se3 and Sb2Te3. Following up on our previous collaborative studies of Raman spectroscopy and first-principles DFT, which revealed an electronic topological transition (ETT) with pressure, we performed non-contact conductivity measurements using a tunnel diode oscillator (TDO) circuit under high pressure in a diamond anvil cell. A Fermi Surface (FS) is found to appear at 6.4 GPa. We also find evidence for a Berry phase (β) of value π independent of magnetic field orientation, indicating possible non-trivial topologies. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V02.00002: Electronic Transport Properties of few-layer PdTe2 Guixin Cao, Ruoyu Chen, Dongying Wang, Marc Bockrath, Chun Ning Lau The interplay of superconductivity and topological states in layered transition-metal dichalcogenide materials have attracted much attention due to their possible promise to realize topological superconductors. PdTe2 is one of such compounds that exhibit coexistence between two-dimensional superconductivity and topological states. We report experimental investigations on the electrical transport and magnetic properties of mechanically exfoliated single crystal PdTe2 bulk and few layers. Latest data as function of layer thickness, temperature and magnetic field will be reported. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V02.00003: Observation of Quantum Oscillations in PdTe2 Single Crystals Ramakanta Chapai, David E Graf, John Ditusa, Rongying Jin Transition-metal dichalcogenide PdTe2 exhibits superconductivity and topologically non-trivial surface states. Here, we present a detailed study of the de-Haas van Alphen (dHvA) oscillations in single crystalline PdTe2. In analyzing the magnetic field dependence of the magnetization and magnetic torque, we identify two frequencies from the oscillations: Fα = 8 T and Fβ = 117 T. Using the Lifshitz-Kosevich equation to fit experimental data, the effective masses are obtained with m*α = 0.059m0 and m*β = 0.067m0 (m0 is the free electron mass). Further analysis of the dHvA oscillations reveals that the α band possesses a non-trivial Berry phase (~ 0.94π) while the β band consists of a smaller Berry phase (~ 0.32π). This indicates that the α band is likely responsible for the topological properties. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V02.00004: Surface Repair and Passivation of InAs Quantum Wells with ALD Sebastian Pauka, James Witt, Cioffi Nicole Murphy, Geoffrey C. Gardner, Sergei Gronin, Tian Wang, Candice Thomas, Michael Manfra, David Reilly, Maja C Cassidy The two-dimensional electron gas formed in InAs quantum wells and proximitized with epitaxially grown Aluminium has attracted interest as a possible host for Majorana zero modes. This is due to the strong spin-orbit coupling and large Landé g-factor in this material. However, the need to induce superconductivity in the quantum well requires it to be grown close to the surface (~12nm), making the 2DEG highly sensitive to any processing. In particular, the aluminium etch, typically a Transene-based wet etch, has limited measured mobility in InAs quantum wells. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V02.00005: Core-Shell Nanowires of 3D Topological Insulators Kevin Geishendorf, Tommi Paavo Tynell, Kornelius Nielsch, Andy Thomas Topological insulators (TI) are promising candidates for next generation electronic/spintronic devices. The gapless surface states (SS) in TI exhibit a very high mobility and strongly suppressed backscattering due to spin-momentum locking. However, to exploit those advantageous one has to decrease the finite bulk conductance present in most TI systems. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V02.00006: Measurement of g-factor in InAs and InAs.5Sb.5 Surface Quantum Wells Mehdi Hatefipour, Joseph Yuan, William Andrew Mayer, Kaushini Wickramasinghe, Wendy L. Sarney, Stefan P. Svensson, Javad Shabani The rising interest into topological superconductors has led to the exploration of hybrid superconductor-semiconductor structures. In these structures two dimensional electron gases are confined near surface and can make epitaxial contact to superconducting thin films. Large Zeeman splitting and spin orbit coupling are necessary ingredients to look for when choosing the semiconductor. Here we present findings of our experiments on two prime candidates with strong spin orbit interaction and high g-factor: InAs and InAs.5Sb.5. We measure weak anti-localization signal and integer quantum hall energy gaps as a function of carrier density in near surface quantum wells of both materials. We use fitting of weak anti-localization to determine strength of spin orbit interaction and the energy gaps of odd Integer quantum Hall states (v=3 and v=5) to extract g-factors. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V02.00007: Current-induced nuclear spin polarization effects in Bi(111) film flakes with strong spin-orbit interaction Zijian Jiang, Victoria Soghomonian, Jean Heremans The influence on quantum transport of nuclear spin polarization, induced by hyperfine interactions and the Edelstein effect, was investigated in individual micrometer-size 40 nm thick Bi(111) film flakes. The flakes were obtained by exfoliation and PDMS stamping from epitaxial Bi(111)-on-mica films. The growth method will be discussed. AFM and SEM micrographs of the Bi(111) film clearly show micrometer-size triangular structured islands with 0.4 nm step height (Bi(111) bilayer height). At low temperatures a high current density is applied to generate nonequilibrium carrier spin polarization by the Edelstein effect, which then induces nuclear polarization by hyperfine interactions and dynamic nuclear polarization. The low-temperature quantum transport measurements are carried out both before and after the current application. The quantum phase coherence time and the spin-orbit scattering time are obtained by fitting of weak-antilocalization magnetotransport data. In our Bi(111), the phase coherence time and the spin-orbit scattering time show a dependence on the nuclear spin polarization obtained by hyperfine interactions with the spin-polarized carriers, in turn obtained by the Edelstein effect. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V02.00008: Topological Hall Effect in Dual-gated Magnetic Topological Insulator Heterostructures Run Xiao, Di Xiao, Jue Jiang, Morteza Kayyalha, Jae Ho Shin, Fei Wang, Ling Zhang, Jianxiao Zhang, Chaoxing Liu, Moses H W Chan, Cui-Zu Chang, Nitin Samarth Magnetic chiral spin textures in real space serve as excellent model systems for fundamental studies of Berry curvature physics. The interaction of itinerant charge carriers with chiral spin textures induces an excess Hall voltage known as a ‘topological Hall (TH) effect,’ providing an indirect signature of non-trivial spin textures in transport measurements. Here, we report the observation of a possible TH effect in a heterostructure that sandwiches a topological insulator (TI) layer in between two magnetic TI layers. By varying the chemical potential using top and bottom gates, we map out the behavior of the TH effect and show that it is greatly enhanced when the chemical potential difference between the two surfaces is increased. This observation suggests that the excess Hall voltage is a result of a finite Dzyaloshinskii-Moriya interaction induced by the magnetization asymmetry in two magnetic layers. Apart from providing new insights into the TH effect, our study paves a new route for demonstrating proof-of-concept topological spintronic devices that rely on the interplay between momentum- and real- space spin textures. |
Thursday, March 7, 2019 4:06PM - 4:42PM |
V02.00009: Surface State Transport in 3D Topological Insulators Invited Speaker: Nadya Mason In this talk, I will discuss transport measurements of the topological surface state of the 3D TI Bi2Se3. By carefully configuring devices and controlling doping levels, we are able to demonstrate the unique properties of surface transport. In particular, we show that the supercurrent flows primarily through surface states in TI-superconductor junctions, that there is ballistic surface transport in nanowires exhibiting Aharonov-Bohm effects, and that finite momentum shifts of Cooper pairs is evident in superconducting junctions studied via Fraunhofer spectroscopy. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V02.00010: Accessing the intrinsic spin transport in a topological insulator with a four-probe scanning tunneling microscope Wonhee Ko, Giang Nguyen, Hoil Kim, Jun Sung Kim, Xiaoguang Zhang, An-Ping Li The electrical transport through topologically protected surface states in topological insulators is expected to exhibit superior mobility from prohibited backscattering and spin-polarized current from spin-momentum locking. However, access to the intrinsic transport properties of surface states remains an experimental challenge, due to the extrinsic effects such as device geometry and environmental contaminations. Here, we directly access the intrinsic surface conductance of topological insulators by using a four-probe scanning tunneling microscope to tune the crossover of bulk-to-surface conductance. By controlling the probe-spacing and temperature, we realize 100 % surface conductance on the bulk single crystal of Bi2Te2Se. It allows us to measure more than an order of magnitude higher surface carrier mobility than the bulk, and a spin polarization approaching theoretically predicted value. A scattering-free spin transport is revealed at micrometer scale through topological surface states. In this manner, we achieve a direct and quantitative measurement of the intrinsic spin-polarized transport associated with topological surface states. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V02.00011: Acoustic Polaron on the Surface of Topological Insulators Jiantao Kong, Alexander Shvonski, Krzysztof Kempa We report a plasmon-polaron mode of a 2D electron gas occupying the surface states of a 3D |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V02.00012: Energy Dependence of the Photogalvanic Effect in a Bi2Se3 Nanoflake Device Seyyedesadaf Pournia, Giriraj Jnawali, Howard E Jackson, Leigh Smith, Ryan Need, Stephen Wilson Bi2Se3 is a prototypical topological insulator exhibiting gapped bulk states with topologically protected conducting surface states. Here we study the linear photogalvanic effect (LPGE) in a Bi2Se3 nanoflake device as a function of energy from 0.3 to 1.8 eV. At 800 nm (1.5 eV) with the laser polarized parallel to the current, we measure a positive or negative response when the laser excitation is close to one of the contacts. Fixing the laser at the peak response, we measuring the energy dependence of the LPGE as we scan from 0.3 eV to 1.8 eV. Peaks are seen at 0.35 eV, and other higher lying optical transitions. We modulate the 800 nm excitation laser between left and right circularly polarized light observing, when current flows, positive and negative peaks at the edge of the nanosheet in line scans, consistent with a spin-Hall effect. |
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