Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L10: Two Dimensional Topological Insulators: Experiments |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Sean Oh, Rutgers University Room: 007A |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L10.00001: Emergence and coupling of topological surface states in tunable TI-non TI heterostructures Nikesh Koirala, Matthew Brahlek, Jianpeng Liu, Maryam Salehi, Tahir Yusufaly, David Vanderbilt, Seongshik Oh The most distinctive feature of topological insulators (TI) is the topologically protected surface states (TSS) that reside at the interface between TI and trivial insulators (non-TI). These TSS have been difficult to probe with transport measurements so far due to deleterious bulk conduction. Using atomically engineered TI -- non TI heterostructures, we have studied the emergence and coupling of TSS at TI-non TI interfaces by tuning the thickness and transparency of the non-TI layer. Theoretical analysis based on first principle calculations as well as tunneling model are fully consistent with the observed experimental results and altogether provide a coherent picture of evolution of TSS at TI - non TI interface in such tunable heterostrucutres. Being near ideal systems for tuning TSS and allowing them to be probed via transport measurement such heterostructures open will new avenues for future research and applications. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L10.00002: Effect of in-plane magnetic field and strain to quantization in 2D topological insulator: application to InAs/GaSb Quantum Wells Lun-Hui Hu, Dong-Hui Xu, Jinhua Sun, Yi Zhou, Fu-Chun Zhang Motivated by the recent discovery of quantized spin Hall effect in InAs/GaSb quantum wells [1,2], we theoretically study the effects of in-plane magnetic field and strain effect to the quantization of charge conductance by using Landauer-Butikker formalism. Our theory predicts a robustness of the conductance quantization against the magnetic field up to a very high field of 20 tesla. We use a disordered hopping term to model the strain and show that the strain may help the quantization of the conductance. Relevance to the experiments will be discussed. \\[4pt] [1] Donghui [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L10.00003: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L10.00004: Tuning the Fermi level through the Dirac point of giant Rashba semiconductor BiTeI Derrick VanGennep, D.L. Maslov, J.J. Hamlin, S. Maiti, D. Graf, S.W. Tozer, C. Martin, H. Berger We report measurements of Shubnikov-de Haas oscillations in the giant Rashba semiconductor BiTeI under pressure. We observe one high frequency oscillation at all pressures and one low frequency oscillation that emerges between $\sim$0.3 - 0.7 GPa indicating the appearance of a second small Fermi surface. BiTeI has a conduction band bottom that is split into two sub-bands due to the strong Rashba coupling, resulting in a ``Dirac point.'' Our results suggest that the chemical potential starts below the Dirac point in the conduction band at ambient pressure and moves upward, crossing it as pressure is increased. We present a simple model that captures this effect and can be used to understand the pressure dependence of our sample parameters. The parameters extracted via our model support the notion that pressure brings the system closer to the predicted topological quantum phase transition. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L10.00005: Magnetic field-induced breakdown of helical conduction in an InAs/GaSb bilayer Dmitry Pikulin, Timo Hyart, Shuo Mi, Jakub Tworzydlo, Michael Wimmer, Carlo Beenakker We calculate the conductance of a two-dimensional bilayer with inverted electron-hole bands, to study the sensitivity of the quantum spin Hall insulator (with helical edge conduction) to the combination of the perpendicular magnetic field in presence of disorder. The characteristic breakdown field for helical edge conduction splits into two fields with increasing disorder, a field $B_c$ for the transition into a quantum Hall insulator (supporting chiral edge conduction) and a smaller field $B_c'$ for the transition to bulk conduction in a quasi-metallic regime. The spatial separation of the inverted bands, typical for broken-gap InAs/GaSb quantum wells, is essential for the magnetic-field induced bulk conduction -- there is no such regime in HgTe quantum wells. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L10.00006: HgTe/CdTe heterostructure under perturbations preserving time reversal symmetry: a density functional theory study Paulo Piquini, Jonas Anversa, Tome Schmidt, Adalberto Fazzio The Dirac-like spin states at the interfaces of HgTe/CdTe heterostructures are predicted to be robust against perturbations preserving time-reversal symmetry. However, these perturbations will certainly affect these interface states. In this work we use the density functional theory to study the behavior of these interface states under external pressure and electric fields. Differently from the three-dimensional topological insulators, the HgTe/CdTe interface states present fully in-plane Rashba-like spin texture. Further, biaxial external pressures and electric fields perpendicular to the interfaces are seen to change the energetics and dispersion of the protected states, modifying the energy ordering of the crossing of the polarized interface states inside the band structure, and altering their Fermi velocities while not changing the topological quantum phase. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L10.00007: Search for emergent superlattice dispersion in a topological insulator heterostructure Ilya Belopolski, Nikesh Koirala, Suyang Xu, Madhab Neupane, Guang Bian, Nasser Alidoust, Seongshik Oh, Zahid Hasan Crystals are typically offered to us by nature and we must search among them to find ones with useful properties. Here, we consider a more aggressive approach to materials engineering where we build a nanometer-scale periodic array of different crystal lattices. Such a lattice of lattices may allow us to directly engineer desired electronic properties in an emergent superlattice band structure. To our knowledge, no such superlattice dispersion has yet been observed. However, the discovery of topological insulators offers a natural route to engineering a superlattice band structure. Moreover, a topological insulator superlattice has immediate relevance as a way to engineer a Weyl semimetal. Other superlattices which give rise to other unusual phases may also exist. Here, we use photoemission spectroscopy to study a one-dimensional superlattice of alternating layers of a topological insulator, Bi$_2$Se$_3$, and a conventional insulator, In$_x$Bi$_{2-x}$Se$_3$. This system has a phase transition to a topological phase, which we search for by changing the thickness of the topological and trivial layers, as well as the In doping $x$ in the trivial layer. Despite evidence in favor of a superlattice dispersion, we cannot yet conclude that we have achieved a superlattice band structure. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L10.00008: Quantum Confined Sb: An Elemental Topological Insulator Shayne Cairns, Jeremy Massengale, Zhonge-He Liu, Joel Keay, Chomani Gaspe, Kaushini Wickramasinghe, Tetsuya Mishima, Michael Santos, Sheena Murphy Sb is a bulk semi-metal which is predicted to undergo a series of quantum phase transitions from a topological semi-metal to a 3D topological insulator (TI) to a 2D TI to a trivial insulator as a function of decreasing film thickness. We report magneto-transport studies on Sb(111) epilayers with thicknesses ranging from 0.7 to 3.2 nm grown via molecular beam epitaxy on nearly lattice-matched GaSb(111) substrates. For thicknesses greater than 1nm the films are conducting with a non-zero intercept at zero film thickness, indicating residual surface conduction. Below 1nm, there is an abrupt transition to insulating behavior consistent with predictions of a topological to trivial insulator. We have studied the magneto-resistance (MR) up to 18T in both perpendicular and tilted magnetic fields for a range of temperatures. The angular MR indicates 2D transport. For (B>4T) the MR is increasingly linear as the film thickness is reduced while at lower fields the transport is well described by weak antilocalization (WAL). A straightforward model combing bulk behavior and WAL assists in explaining this thickness evolution. Experiments on quantum interference in quantum wires are ongoing. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L10.00009: Role of Coulomb Interaction in the Bulk Gap of inverted InAs/GaSb bilayers Lingjie Du, Rui-Rui Du, Gerard Sullivan Inverted InAs/GaSb bilayers have been shown to support the quantum spin Hall effect, characterized by an insulating 2D bulk and a Kramer's pair of counter propagating 1D helical edge states. Since the Fermi energy of electrons and that of holes can be individually turned by gates, the degree of band inversion can be readily controlled in experiments. Here we perform the inplane field magneto-measurement of InAs/GaSb samples, in the two limits of band inversion. In the deeply inverted regime where electron and hole density exceed 10e11/cm2, we found that the bulk gap closes under several Tesla field, consistent with previous results in the same regime (M. J. Yang et al, Phys. Rev. Lett. 78, 4613). On the other hand, in the shallowly inverted regime close to inverted-normal band transition we find that the bulk gap remains open to very high fields (up to 35T). These results suggest that the nature of the bulk gap in InAs/GaSb in the shallowly inverted regime is not well understood. We will discuss the possible role of Coulomb interaction in this regime, where dilute electron-hole gases are unstable against the formation of bilayer exciton. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L10.00010: Observation of giant supercurrent states in a superconductor-InAs/GaSb-superconductor junction Xiaoyan Shi, Wenlong Yu, Zhigang Jiang, B. Andrei Bernevig, W. Pan, S.D. Hawkins, J.F. Klem We report observations of the proximity effect induced giant supercurrent states in an InAs/GaSb bilayer system that is sandwiched between two superconducting tantalum electrodes to form a superconductor-InAs/GaSb-superconductor junction. Electron transport results show that the supercurrent states can be preserved in a surprisingly large temperature-magnetic field (T-H) parameter space. In addition, the evolution of differential resistance in T and H reveals an interesting superconducting gap structure. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L10.00011: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L10.00012: Edge-mode superconducting transport in InAs/GaSb heterostructures Fanming Qu, Vlad Pribiag, Arjan Beukman, Maja Cassidy, Leo Kouwenhoven, Christophe Charpentier, Werner Wegscheider Type-II InAs/GaSb heterostructures have recently attracted interest as a two-dimensional topological insulator that can be tuned between the trivial and topological phases by means of electrostatic gating. In proximity to a superconductor, 2D topological insulators are predicted to host Majorana fermions, a consequence of the helical nature of the edge-modes. Here we report superconductivity mediated by the edge-modes of InAs/GaSb quantum wells. Using superconducting quantum interference, we demonstrate tuning between edge-dominated and bulk-dominated superconducting transport regimes as a function of electrostatic gating. These experiments establish InAs/GaSb as a robust platform for further investigations of Majorana physics. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L10.00013: Ultra Low Temperature Conductance of Helical Edge States in InAs/GaSb 2D Topological Insulator Tingxin Li, Xiaoyang Mu, Xiaoxue Liu, Pengjie Wang, Hailong Fu, Xi Lin, Kate Schreiber, Gabor Csathy, Lingjie Du, Gerard Sullivan, Rui-Rui Du Inverted InAs/GaSb quantum wells have been shown to be a 2D topological insulator hosting helical edge states. For mesoscopic samples, quantized conductance plateaus of 2e$^{2}$/h have been observed. On the other hand, the longitudinal resistance in long samples increased linearly with device length, indicating certain scattering processes occurred in the helical edge. Moreover, edge states of InAs/GaSb system have a small Fermi velocity \textit{V\textunderscore F}, suggesting that interaction effects may play an important role in their electronic transport properties. We report work in progress for conductance measurements of InAs/GaSb helical edge states in ultra low temperatures. Experiments are performed in two millikelvin dilution refrigerators instrumented for fractional quantum Hall effect studies, one of them having attained 6mK electron temperature. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L10.00014: Quantum Hall Effect on Surface States of Topological Insulator (Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$)$_{2}$Te$_{3}$ Thin Films Ryutaro Yoshimi, Atsushi Tsukazaki, Yusuke Kozuka, Joseph Falson, Kei Takahashi, Joseph Checkelsky, Naoto Nagaosa, Masashi Kawasaki, Yoshinori Tokura The three-dimensional (3D) topological insulator (TI) is a novel state of matter as characterized by two-dimensional metallic Dirac states on its surface. Quantum transport in Dirac systems has been attracting much attention for the half-integer quantum Hall effect (QHE), as typically observed in graphene. Unlike the case of graphene, the Dirac states of TIs have no degeneracy including spin degree of freedom. Instead, both top and bottom surfaces host Dirac states with opposite spin-momentum locked modes. Such a helicity degree of freedom in real space is expected to yield intriguing quantum phenomena in 3D TIs. Bi-based chalcogenides such as Bi$_{2}$Se$_{3}$, Bi$_{2}$Te$_{3}$, Sb$_{2}$Te$_{3}$ and their compounds are candidates where the Dirac features can be detected via quantum transport phenomena in thin films form. Here, we report the realization of the QHE on the surface Dirac states in (Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$)$_{2}$Te$_{3}$ films ($x=$0.84 and 0.88). With electrostatic gate-tuning of Fermi level under magnetic fields, QH states with filling factor $\nu =\pm $1 are resolved with quantized Hall resistance of $R_{\mathrm{yx}}=\pm h$/$e^{2}$ and zero $R_{\mathrm{xx}}$, owing to the chiral edge modes at top/bottom surface Dirac states. The significant technical advance in 3D TI films may pave a way toward TI-based electronics. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L10.00015: Experimental Analysis of Weak Anti-localization in Topological Insulator Thin Films Jisoo Moon, Namrata Bansal, Matthew Brahlek, Nikesh Koirala, Seongshik Oh The weak anti-localization (WAL) effect, seen as a sharp cusp in resistance vs magnetic field at small fields, is quantified by the Hikami-Larkin-Nagaoka (HLN) formalism that yields information about the effective number of 2D conducting channels in terms of the parameter A. In thin-film Bi$_{2}$Se$_{3}$, A has a typical value of 1, even if the ideal value is 2 that occurs if top and bottom surfaces are decoupled. We show that this is due to bulk being metallic. On depleting the bulk carriers, the value of A increases to 2, though only if the film is thick enough. In the ultra-thin regime, \textless 6 nm, a gap is formed at the Dirac point; A remains 1 if the Fermi level is away from Dirac point and into the conduction band, and only drops to 0 when Fermi level is tuned into the Dirac gap, though this occurs only for thin films with high mobility. In case of highly disordered films with poor carrier mobilities, the value of A can change from 1 to 0 as the film thickness is reduced, even if the Fermi level is away from Dirac gap. We provide a coherent picture of how A evolves depending on disorder, bulk properties and film thickness. [Preview Abstract] |
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