Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R3: Theory and Experiment on Three-Dimensional Topological Insulators |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Xiao Li, University of Maryland Room: 262 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R3.00001: Large Unidirectional Magnetoresistance in a Magnetic Topological Insulator Kenji Yasuda, Atsushi Tsukazaki, Ryutaro Yoshimi, Kei Takahashi, Masashi Kawasaki, Yoshinori Tokura Interactions between conduction electrons and magnetization yield various kinds of magnetoresistance. Among them, current-direction dependent or unidirectional magnetoresistance (UMR) has recently been found as a nonlinear current-voltage characteristic for heterostructures composed of ferromagnet and normal metal. Here, we report on the UMR in magnetic/nonmagnetic topological insulator (TI) heterostructures, Cr$_{\mathrm{x}}$(Bi$_{\mathrm{1-y}}$Sb$_{\mathrm{y}})_{\mathrm{2-x}}$Te$_{\mathrm{3}}$/(Bi$_{\mathrm{1-y}}$Sb$_{\mathrm{y}})_{\mathrm{2}}$Te$_{\mathrm{3}}$ thin films, that is shown to be several orders of magnitude larger than those in other previously reported systems. From the angular, magnetic field and temperature dependence, the UMR is identified to originate from the asymmetry in scattering of surface Dirac electrons by magnons. In particular, the large magnitude of UMR is an outcome of spin-momentum locking and small Fermi wavenumber at the surface state of TI. In fact, with changing the Fermi energy, the UMR can be maximized around the Dirac point with the minimal Fermi wavenumber. [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R3.00002: Magneto-transport at the crossover of the three-dimensional topological insulator to the two-dimensional limit in proximity with a ferromagnetic insulator David Rakhmilevitch, Cui-Zu Chang, Weiwei Zhao, Moses H. W. Chan, Jagadeesh S. Moodera The spin-momentum locked electrons on the Dirac surface states of topological insulators (TIs) allow the observation of novel magneto-transport effects. Specifically, combining a TI with a ferromagnetic (FM) perturbing medium can lead to many exotic quantum phenomena. Here, we investigate hetero-structures of FM insulator on top of intrinsic TIs, with the TI film thickness at the crossover of a three-dimensional (3D) TI into a two-dimensional (2D) limit. Taking advantage of an effective electrostatic gating influence on the chemical potential, we systematically investigate the transport properties of such hetero-structures as a function of applied magnetic field and successfully isolate the surface-dominated magneto-transport effects. Our findings shed light on the different contributions of orbital and spin degree of freedoms in magnetized TIs and highlight the role of the Dirac surface states on magneto-transport. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R3.00003: Competing Adiabatic Thouless Pumps in Enlarged Parameter Spaces Pouyan Ghaemi, Pedro Leopoldo e Silva Lopes, Shinsei Ryu, Taylor L. Hughes The transfer of conserved charges through insulating matter via smooth deformations of the Hamiltonian is known as quantum adiabatic, or Thouless, pumping. Central to this phenomenon are Hamiltonians whose insulating gap is controlled by a multi-dimensional (usually two-dimensional) parameter space in which paths can be defined for adiabatic changes in the Hamiltonian, i.e., without closing the gap. Here, we extend the concept of Thouless pumps of band insulators by considering a larger, three-dimensional parameter space. We show that the connectivity of this parameter space is crucial for defining quantum pumps, demonstrating that, as opposed to the conventional two-dimensional case, pumped quantities depend not only on the initial and final points of Hamiltonian evolution but also on the class of the chosen path and preserved symmetries. We distinguish the scenarios of closed/open paths of Hamiltonian evolution, finding that different closed cycles can lead to the pumping of different quantum numbers, and that different open paths may point to distinct scenarios for surface physics. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R3.00004: Disorder-induced density of states on the surface of a spherical topological insulator Adam Durst We consider a topological insulator of spherical geometry and numerically investigate the influence of disorder on the density of surface states. To the clean Hamiltonian we add a surface disorder potential of the most general Hermitian form, $V = V^0(\theta,\phi) + {\bf V}(\theta,\phi) \cdot {\bf \sigma}$. We expand these four disorder functions in spherical harmonics and draw the expansion coefficients randomly from a 4D Gaussian distribution. For each disorder instantiation, we solve for the energy spectrum via exact diagonalization. Then we compute the disorder-averaged density of states by averaging over 200,000 different instantiations. Disorder broadens the Landau-level delta functions of the clean density of states into peaks that decay and merge together. Increasing disorder strength pushes states closer to zero energy, resulting in a low-energy density of states that becomes nonzero for sufficient disorder, typically approaching an energy-independent saturation value. But for purely spin-dependent disorder with ${\bf V}$ either entirely out-of-surface or entirely in-surface, we identify intriguing disorder-induced features in the vicinity of the Dirac point. These are explained in terms of the breaking (or not) of two chiral symmetries of the clean Hamiltonian. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R3.00005: Semi-classical orbits in spin-orbit coupled three-dimensional SU(2) Landau levels Saavanth Velury, Yi Li Time-reversal invariant generalizations of Landau levels from two to three dimensions gave rise to continuum descriptions of topological insulators in three dimensions. In this talk, we study the corresponding generalization of familiar cyclotron motion of charged particles under a magnetic field to three-dimensional (3D) trajectories with spin-angular momentum locking in 3D Landau levels with a 3D rotationally invariant SU(2) gauge. Because of effective Larmor precession with respect to the spin of the particle, we find that orbits display various spin-orbit coupled motions under different initial conditions. The analogy with a quantum top will also be presented. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R3.00006: Symmetry Rules Shaping Spin-Orbital Textures in Surface States Chiu-Yun Lin, Kenneth Gotlieb, Zhenglu Li, Chris Jozwiak, Ji Hoo Ryoo, Cheol-Hwan Park, Zahid Hussain, Steven G. Louie, Alessandra Lanzara A complete understanding of a surface state subject to strong spin-orbit coupling requires mapping all of its key degrees of freedom. We study topological insulators using spin- and angle-resolved photoemission to elucidate the rules that couple an orbital texture to a spin texture. From this, we demonstrate where in a material's band structure one should expect an orbital-dependent spin texture, and where a surface state can have a single, orbital-independent spin texture. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R3.00007: Theoretical study of SrRu2O6 and related compounds Satoshi Okamoto, Masayuki Ochi, Ryotaro Arita, Jiaqiang Yan, Nandini Trivedi We theoretically investigate the electronic property of a hexagonal compound SrRu$_2$O$_6$ and isostructural CaOs$_2$O$_6$ [1]. Here, we focus on the topological property of these compounds under various strain conditions. Based on an analysis of parity eigenvalues, we anticipate that a three-dimensional strong topological insulating state should be realized when band inversion is induced at the A point in the hexagonal Brillouin zone. We found that such a transition is indeed possible in these compounds under certain strain conditions. In particular, for CaOs$_2$O$_6$, the transition could be induced more easily than SrRu$_2$O$_6$ owing to the stronger spin-orbit coupling and smaller lattice constants. We also investigate the magnetic property of SrRu$_2$O$_6$ using density functional theory. Detailed comparison with experimental reports [2,3] will be presented. [1] M. Ochi {\it et al.}, Phys. Rev. B {\bf 93}, 195149 (2016). [2] W. Tian {\it et al.}, Phys. Rev. B {\bf 92}, 100404(R) (2015). [3] C. I. Hiley {\it et al.}, Phys. Rev. B {\bf 92}, 104413 (2015). [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R3.00008: Direct observation of Landau level resonance and mass generation in three dimensional topological Dirac semimetal thin films Xiang Yuan, Peihong Cheng, Hugen Yan, Zhiqiang Li, Faxian Xiu Three-dimensional topological Dirac semimetals have hitherto stimulated unprecedented research interests as a new class of quantum materials. Breaking certain types of symmetries has been proposed to enable the manipulation of Dirac fermions; and that was soon realized by external modulations such as magnetic fields. However, an intrinsic manipulation of Dirac states, which is more efficient and desirable, remains a significant challenge. Here, we report a systematic study of quasi-particle dynamics and band evolution in Cd3As2 thin films with controlled Chromium (Cr) doping by both magneto-infrared spectroscopy and electrical transport. For the first time, we observe sqrt-B relation of inter-Landau-level resonance, an important signature of ultra-relativistic Dirac state inaccessible in previous optical experiments. A crossover from quantum to quasi-classical behavior makes it possible to directly probe the mass of Dirac fermions. Importantly, Cr doping allows for a Dirac mass acquisition and topological phase transition. Corroborating with the density-functional theory calculations, we show that the mass generation can be explained by the explicit C4 rotation symmetry breaking and the resultant Dirac gap engineering through Cr substitution for Cd atoms. The manipulation of the system symmetry and Dirac mass in Cd3As2 thin films provides a tuning knob to explore the exotic states stemming from the parent phase of Dirac semimetals. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R3.00009: Conductance Spectroscopy of Nb-doped Bi$_2$Se$_3$ C. Kurter, A. D. K. Finck, Y. Qui, E. Huemiller, A. Weis, J. Medvedeva, P. Ghaemi, Y. S. Hor, D. J. Van Harlingen Doped topological insulators provide a promising platform to study 3D topological superconductivity with unconventional pairing symmetry. We present Andreev reflection spectroscopy on Nb-doped Bi$_2$Se$_3$, a candidate 3D topological superconductor. Our samples consist of thin, exfoliated pieces contacted by normal metal leads with varying contact transparency. Broad zero bias conductance peaks of low contact resistance samples reveal clear signatures of Andreev reflection as well as pronounced conductance dips at the superconducting energy gap that cannot be described by the conventional BTK theory. At the lowest temperatures, additional Andreev reflection features appear at low energy signifying the existence of two distinct gaps. There is a strong anisotropy of the upper critical magnetic field between in-plane and out-of-plane directions, suggesting that the thin flakes are in the quasi-2D limit. We discuss our results in the context of p-wave pairing in doped topological insulators. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R3.00010: Topological staggered field-electric effect with bipartite magnets Stefan Rex, Flavio S. Nogueira, Asle Sudbo We theoretically study the interface physics of a bipartite magnetic insulator deposited on a topological insulator (TI), focusing on the topological magnetoelectric (TME) effect that occurs in the presence of a magnetization orthogonal to the TI surface. We show that the TME term can take the opposite sign for the two components of the bipartite magnet within a certain parameter region. In that case, an electric field will - unlike in the usual TME effect - mainly generate a staggered field rather than a net magnetic polarization at the interface. Our model comprises ferrimagnets and ferromagnets with multiple magnetic components per unit cell. Antiferromagnets may be considered as well if a net magnetization is achieved by magnetic doping of the TI. Our fully analytic results are obtained by field-theoretic calculations that account for quantum fluctuations on the surfaces of the TI and the magnetic material. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R3.00011: Bi$_{\mathrm{1}}$Te$_{\mathrm{1}}$: A New Dual Topological Insulator Lukasz Plucinski, M. Eschbach, M. Lanius, C. Niu, E. Mlynczak, P. Gospodaric, J. Kellner, P. Schueffelgen, M. Gehlmann, S. Doering, E. Neumann, M. Luysberg, B. Hollaender, G. Mussler, M. Morgenstern, D. Gruetzmacher, G. Bihlmayer, S. Bluegel, C. M. Schneider We present, a combined theoretical and experimental study on the prediction and verification of the dual topological insulating character of the stoichiometric natural superlattice phase Bi$_{\mathrm{1}}$Te$_{\mathrm{1}}$ $=$ [Bi$_{\mathrm{2}}$]$_{\mathrm{1}}$[Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$]$_{\mathrm{2\thinspace }}$[1]. We identify Bi$_{\mathrm{1}}$Te$_{\mathrm{1}}$ by density functional theory to exhibit a non-trivial time-reversal symmetry-driven character of Z$_{\mathrm{2}} \quad =$ (0; 001) and additionally a mirror-symmetry induced mirror Chern number of v$_{\mathrm{M}} \quad =$ -2, which indicates that Bi$_{\mathrm{1}}$Te$_{\mathrm{1}}$ is both a weak topological insulator (WTI) and a topological crystalline insulator (TCI). The coexistence of the two phenomena preordain distinct crystal planes to host topological surface states that are protected by the respective symmetries. We confirm the stacking sequence of our MBE-grown Bi$_{\mathrm{1}}$Te$_{\mathrm{1}}$ thin films by X-ray diffraction and transmission electron microscopy (STEM), and find clear indications of the TCI and WTI character in the surface spin electronic structure by spin- and angle-resolved photoemission spectroscopy. [1] M. Eschbach et al., arXiv:1604.08886 (2016). [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R3.00012: Observation of a macroscopic topological insulator phase in an assembly of coupled topological insulator nanocrystals Diptiman Sen, Abhishek Banerjee, Oindrila Deb, Kunjalata Majhi, R Ganesan, P. S. Anil Kumar We study an assembly of tunnel coupled topological insulator (TI) nanocrystals. We demonstrate experimentally that a macroscopic topological insulator phase can emerge in this system. Electrical transport measurements on thin films of Bi$_2$Se$_3$ nanocrystals reveal the presence of decoupled top and bottom topological surface states above a certain film thickness. The surface state penetration depth is found to be unusually large, $\sim$ 30nm at 2K, and decreases with increasing temperature. For samples with low film thickness, we observe deviations of the surface state Berry phase from $\pi$ due to hybridization of opposite surface states. This weakens the effective spin-orbit coupling field to as low as $\sim$ 30T at 2K. Remarkably, the topological insulating behavior becomes more pronounced with increasing temperature. Our work exhibits a model TI that is distinct from bulk/single crystal TIs and also displays phenomena that are expected, but normally not accessible in the latter systems. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R3.00013: Ultrafast transient-photocarrier relaxation through the topological surface state of Bi$_{\mathrm{1.5}}$Sb$_{\mathrm{0.5}}$Te$_{\mathrm{1.7}}$Se$_{\mathrm{1.3}}$ Younggwan Choi, ChanJune Zhung, Soon Hee Park, Joonbum Park, Jun Sung Kim, Seongheun Kim, Jaehun Park, Jongseok Lee Using optical-pump terahertz-probe spectroscopy, we investigated an ultrafast photocarrier relaxation behavior in a Bi$_{\mathrm{1.5}}$Sb$_{\mathrm{0.5}}$Te$_{\mathrm{1.7}}$Se$_{\mathrm{1.3}}$ (BSTS) single crystal which is one of the most bulk-insulating topological insulators. Compared to n-type bulk-metallic Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$, we found that BSTS endows distinct behaviors in its photocarrier dynamics; (i) the relaxation time turns out to be several times longer, and (ii) the photoconductance exhibits a nonlinear increase as a function of the pumping power. We discuss these intriguing experimental observations based on a bulk-to-surface carrier injection assisted by the built-in electric field near the surface and electron-phonon scattering. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R3.00014: Circular photon drag effect in a Bi$_{2}$Se$_{3}$ film probed by terahertz emission spectroscopy Sun Young Hamh, Soon Hee Park, Sahng-Kyoon Jerng, Jae Ho Jeon, Seung-Hyun Chun, Jong Seok Lee In these days, an optical pumping of topological insulators has been extensively investigated as a route to control the spin-polarized charge current for the spintronic applications. In this work, we address this issue of the spin-polarized photocurrent generation by using terahertz (THz) emission technique. We monitored the THz electric fields emitted from a Bi$_{2}$Se$_{3}$ film with varying a polarization of incident light and sample azimuth, and observed photon-helicity-dependent THz emission responses which exhibit a clear three-fold periodicity in its sample azimuth dependence. Based on a symmetry analysis related to photocurrent generation processes, we demonstrate that the observed circular anisotropy in the photocurrent originates from the circular photon drag effect, namely, linear and angular momentum transfer from photons to photocarriers. [Preview Abstract] |
Thursday, March 16, 2017 10:48AM - 11:00AM |
R3.00015: Delocalized metallic state on insulating, disordered BiSbTeSe2 thin films -- a test of Z$_{\mathrm{2}}$ protection. RK Gopal, Sourabh Singh, Jit Sarkar, Reshma Patro, Subhadip Roy, Chiranjib Mitra We present thickness and temperature dependent magneto transport properties of bulk insulating and granular BiSbTeSe2 thin films, grown by pulsed laser deposition technique. The temperature dependent resistivity (R-T) of these films is found to be insulating (d$\rho $/dT \textless 0) and resistivity changes thrice the magnitude measured at room temperature as temperature is varied from 300K to 1.8K. On application of small perpendicular magnetic field in the low temperature regime, the R-T takes an upward shift from the zero field R-T - a trademark signature of a metallic state on an insulating bulk film. The grain boundaries in these films, as seen by scanning electron microscopy, present an additional disorder and hence confinement/trapping centers to the surface Dirac states in comparison to the films grown by molecular beam epitaxy and single crystals, which have atomically flat surface. Therefore these films present real test for the topological protection of surface Dirac states and their immunity against localization which is known as Z2 protection. From the magnetoresistance (MR) measurements at low temperatures a sharp and relatively large rise in MR is found a signature of weak -- antilocalization (WAL) -a signature of topologically protected surface states. The WAL analysis of the MR data reveals a phase breaking length of the order of grain size suggesting that grain [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. |
© 2020 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700