Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A03: Interactions and Dynamics in Topological Systems |
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Sponsoring Units: DCMP Chair: Madhab Neupane, University of Central Florida Room: BCEC 107B |
Monday, March 4, 2019 8:00AM - 8:12AM |
A03.00001: Impurity-engineered Dirac nodes in three-dimensional topological insulators Anna Pertsova, Alexander V. Balatsky
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Monday, March 4, 2019 8:12AM - 8:24AM |
A03.00002: Distinct multiple fermionic states in a single topological metal. Madhab Neupane, Md Mofazzel Hosen, Klauss Dimitri, Ashis Kumar Nandy, Alex Aperis, Raman Sankar, Gyanendra Dhakal, Pablo Maldonado, Firoza Kabir, Christopher Sims, Fangcheng Chou, Dariusz Kaczorowski, Tomasz Durakiewicz, Peter Oppeneer Among the quantum materials that have recently gained interest are the topological insulators, wherein symmetry-protected surface states cross in reciprocal space, and the Dirac nodal-line semimetals, where bulk bands touch along a line in k-space. However, the existence of multiple fermion phases in a single material has not been verified yet. Using angle resolved photoemission spectroscopy (ARPES) and first principles electronic structure calculations, we systematically study the metallic material Hf2Te2P and discover properties, which are unique in a single topological quantum material. We experimentally observe weak topological insulator surface states and our calculations suggest additional strong topological insulator surface states. Our first-principles calculations reveal a one-dimensional Dirac crossing—the surface Dirac-node arc—along a high-symmetry direction which is confirmed by our ARPES measurements. This novel state originates from the surface bands of a weak topological insulator and is therefore distinct from the well-known Fermi arcs in semimetals. |
Monday, March 4, 2019 8:24AM - 8:36AM |
A03.00003: Spin valve-like magnetoresistance of a topological insulator in proximity to a perpendicular magnet Junseok Oh, Vincent Humbert, Joseph Sklenar, Timothy Philip, Mark Hirsbrunner, Bora Basa, Matthew Gilbert, Nadya Mason Topological insulators (TIs) have a variety of unique transport properties, one of which is symmetry-protected surface states. Efforts have been made to control the surface states by symmetry breaking via proximity magnetization, which is typically achieved by placing a ferromagnetic or antiferromagnetic insulator in direct contact with the TI. We report a spin valve-like magnetoresistance switching phenomena when the TI Bi2Se3 is in contact with a Co/Pt multilayer, which has a perpendicular magnetic anisotropy. The magnetoresistance is mostly isotropic, as evidenced by the resistance switching when either in-plane or out-of-plane magnetic fields are applied. This effect occurs at low temperatures, and the switching fields are incompatible with the behavior of Co/Pt. It appears the phenomenon is related to a magnetized TI surface and/or bulk states. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A03.00004: Observation of Two Magnetically Inequivalent Regions in SmB6 at Low Temperatures Jeff Sonier, Kolawole Akintola, Shayan Gheidi, Sarah R Dunsiger, Andre Cote, Shanta Saha, Johnpierre Paglione, Wesley T Fuhrman, Collin Broholm The temperature dependence of the μSR relaxation rate in SmB6 exposed to a high transverse magnetic field (TF) was recently shown to exhibit thermally-activated behavior for 4 K < T < 20 K, consistent with the freezing out of a bulk low-energy (~ 1 meV) spin exciton [K. Akintola et al., npj Quantum Materials 3:36 (2018)]. However, a 1 meV magnetic excitation has never been observed in neutron scattering measurements, all of which have been performed on the same floating-zone grown double-isotope 154Sm11B6 single crystal. In an attempt to understand why, we have performed zero-field (ZF) and longitudinal-field (LF) μSR measurements on the 154Sm11B6 and Al-flux grown SmB6 single crystals. The μSR signals show greater relaxation in the 154Sm11B6 single crystal, and reveal the development of slow and fast relaxing components below T ~ 20 K. The volume fraction of the slower relaxing component grows to ~ 70 % at T = 2 K. While the relaxation rates are smaller, the volume fractions of the two components are similar in the Al-flux grown SmB6 crystals. This suggests that the source of the two components is intrinsic and originates from spatially distinguishable regions in the sample. |
Monday, March 4, 2019 8:48AM - 9:00AM |
A03.00005: Band structure engineering in short period Bi2Se3/Sb2Te3 superlattices grown by molecular beam epitaxy Ido Levy, Thor A. Garcia, Haiming Deng, Steven J. Alsheimer, Lia Krusin-Elbaum, Maria Tamargo When grown by molecular beam epitaxy (MBE) Bi2Se3 is n-type and Sb2Te3 is p-type due to selenium vacancies and anti-site defects, respectively. To capitalize on the unique topological surface properties of these materials it is essential to reduce the bulk carriers. Compensation doping is a way to do that, but that method requires accurate dopant incorporation levels that are difficult to achieve. In this work we explore the use of p-n-p-n short-period superlattices (SLs) to accomplish this goal. A series of Bi2Se3/Sb2Te3 short-period SLs with varying period thicknesses and Bi2Se3 to Sb2Te3 thickness ratios were grown by MBE. The samples were characterized by high resolution x-ray diffraction (HR-XRD) and transport measurements. Using HR-XRD we determine the change in effective composition and SL period for the samples. We observed a dependence of bulk background doping on the SL period thickness: lower carrier density for thinner SL period. We interpret this as the formation of a gap due to quantum confinement effects. A preservation of a weak anti-localization (WAL) cusp, typical of topological surface features, was observed by magnetoconductance. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A03.00006: Effects of Nitrogen Exposure on the Bismuth Selenide Density of States Michael Gottschalk, Mal-Soon Lee, Camille Mikolas, Eric Goodwin, Thomas Chasapis, Mercouri Kanatzidis, S Mahanti, Stuart Holden Tessmer Bi2Se3 is a topological insulator widely used for scientific studies due in part to the ease with which it can be cleaved, exposing a clean surface for study. Typically the materials exhibit n-type doping attributed to selenium vacancies which results in a shift of the Dirac point to more than 100 meV below the Fermi level. Using cryogenic scanning tunneling microscopy (STM), we observed a shift in the expected density of states spectra when the crystals were cleaved in a pure nitrogen gas environment. The shift tends to restore the Dirac point to the Fermi level. These results are compared against crystals cleaved in a pure helium gas environment which reproduces the expected pristine spectra. We will present density functional theory calculations supporting the picture that nitrogen can bind to the selenium vacancies and shift the density of states. Furthermore, we will present data showing an upper-bound on the level of gas exposure necessary for saturated adsorption. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A03.00007: Topology of the Valley-Chern Effect Kai Qian, David J. Apigo, Camelia Prodan, Yafis Barlas, Emil Prodan In this talk, we investigate the quantum valley-Hall effect (QVHE) using a versatile experimental platform based on magnetically coupled spinners. We demonstrate that this regime is not suitable for metamaterial applications due to the delocalization of the interface modes. The enlargement of the bulk gap needs to be accompanied by a Berry curvature engineering that keeps it localized near the valleys. This is a new effect which we call the valley-Chern effect (VCE). By establishing an exact relation between VCE and QVHE, we demonstrate a robust bulk-boundary principle, which could be the foundation of a new wave of applications of topological metamaterials. |
Monday, March 4, 2019 9:24AM - 9:36AM |
A03.00008: Observation of topological edge modes in a quasi-periodic acoustic waveguide Wenting Cheng, David J. Apigo, kyle dobiszewski, Emil Prodan, Camelia Prodan We present a system of acoustic waveguide generated by a simple quasi-periodic patterning without any additional fine-tuning. The system presents topological edge modes. The waveguides are characterized experimentally by standard acoustic measurements, and via a finite element approach utilizing COMSOL Multiphysics. The experimental results and simulations confirm the existence of topological edge modes in these gaps. |
Monday, March 4, 2019 9:36AM - 9:48AM |
A03.00009: A Proposal to Detect Dark Matter Using Axionic Topological Antiferromagnets David James Edward Marsh, Kin Chung Fong, Erik Lentz, Libor Smejkal, Mazhar Ali Astrophysical and cosmological observations of the last 40 years provide strong evidence for the existence of non-baryonic dark matter. Among possible candidates are dark axions, hypothetical particles suggested to solve the CP problem in quantum chromodynamics. It is known that magnetically doped topological insulators can become "axionic insulators" and host axionic excitations. In particular, antiferromagnetically doped topological insulators (A-TI) are among the candidates to host dynamical axion fields and axion-polaritons. Here we demonstrate that using the axion quasiparticle and antiferromagnetic fluctuations in A-TI's in conjunction with low-noise methods of detecting THz photons presents a viable route to detect axion dark matter with mass 0.7 to 3.5 meV, a range currently inaccessible to all other dark matter detection experiments and proposals. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A03.00010: Dzyaloshinskii-Moriya Interaction on Surfaces of Topological Insulator Domenico Andreoli, Chao-Xing Liu, Jiadong Zang The Topological Hall Effect (THE) is a hallmark of nontrivial spin texture. In this work we theoretically study the THE is realizable in centrosymmetric materials. The only requirement being that local inversion symmetry is broken. To show that the THE can occur we start with the model of surface states of a Topological Insulator (TI) and include magnetization on the top and bottom surfaces of the TI. From here the Spin Susceptibility (SS) tensor is determined numerically and it is shown to have off-diagonal components. These components are then related to the Dzyaloshinskii-Moriya (DM) vector. Demonstration of nonzero DM interaction on the surfaces of the TI reveals nontrivial topology in the real space, along with the nontrivial electronic band structure of the TI in momentum space allows for the possibility of the THE in centrosymmetric materials. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A03.00011: Valley-Chern Effect with LC-Resonators: A Modular Platform Yishai Eisenberg, Yafis Barlas, Emil Prodan The valley Chern-effect is theoretically demonstrated with a novel alternating current circuitry, where closed-loop LC-resonators sitting at the nodes of a honeycomb lattice are inductively coupled along the bonds. This enables us to generate a dynamical matrix which copies identically the Hamiltonian driving the electrons in graphene. The valley-Chern effect is generated by splitting the inversion symmetry of the lattice. After a detailed study of the Berry curvature landscape and of the localization of the interface modes, we derive an optimal configuration of the circuit. Furthermore, we show that Q-factors as high as $10^4$ can be achieved with reasonable materials and configurations. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A03.00012: LONG RANGE DYNAMICAL COUPLING BETWEEN MAGNETIC ADATOMS MEDIATED BY EDGE STATES IN A 2D TOPOLOGICAL INSULATOR Marcio Costa, Marco Buongiorno Nardelli, Adalberto Fazzio, Antônio Costa We study the spin excitation spectra and the dynamical exchange coupling between iron adatoms on a bismuthene nanoribbon. We show that the topological character of the edge states is preserved in the presence of the magnetic adatoms. Nevertheless, they couple significantly to the edge spin currents, as witnessed by the large and long-range dynamical coupling we obtain in our calculations. The large effective magnetocrystalline anisotropy of the magnetic adatoms combined with the transport properties of the topologically protected edge states make this system a strong candidate for implementation of spintronics devices. We use a multi-orbital tight-binding Hamiltonian to describe the electronic structure of the decorated nanoribbon. The full Hamiltonian can be written as the sum of band energy H0, effective intra-atomic Coulomb repulsion HI and the atomic spin-orbit coupling HSOC. The hopping matrix is obtained directly from a DFT calculation using the pseudo-atomic orbital projection method[1]. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A03.00013: Topological Logical Gates with Meta-Materials Emil Prodan, Yafis Barlas Recently, the classification table of strong topological |
Monday, March 4, 2019 10:36AM - 10:48AM |
A03.00014: Interacting Topological Insulators with Synthetic Dimensions Chao-Ming Jian, Cenke Xu Recent developments of experimental techniques have given us unprecedented opportunities of studying topological insulators in high dimensions, while some of the dimensions are "synthetic", in the sense that the effective lattice momenta along these synthetic dimensions are controllable periodic tuning parameters. In this work, we study interaction effects on topological insulators with synthetic dimensions. We show that although the free fermion band structure of high dimensional topological insulators can be precisely simulated with the ``synthetic techniques", generic interactions in these effective synthetic topological insulators are qualitatively different from the local interactions in ordinary condensed matter systems. And we show that these special but generic interactions have unexpected effects on topological insulators, namely they would change (or reduce) the classification of topological insulators differently from the previously extensively studied local interactions. |
Monday, March 4, 2019 10:48AM - 11:00AM |
A03.00015: Anomalous Josephson supercurrent in bulk-insulating topological insulator BiSbTeSe2 Subhamoy Ghatak, Oliver Breunig, Fan Yang, Zhiwei Wang, Alexey A Taskin, Yoichi Ando Three dimensional topological insulators (3D-TIs) have recently drawn a considerable interest due to their spin-helical surface band structure. The Josephson junctions made of these 3D-TIs, by proximitizing with s-wave superconductors, are predicted to harbour 1D- Majorana modes. While observations of supercurrent in 3D-TI-based Josephson junctions are recently reported, the Fraunhofer patters observed in such topological Josephson junctions, which sometimes present anomalous features, are still not well understood. In this talk, I will discuss about our study on highly gate-tunable topological Josephson junctions made of bulk-insulating TI materials, BiSbTeS2. The Fermi level can be tuned by gating across the Dirac point, and the high transparency of the Al/BiSbTeSe2 interface is evinced by high multiple Andreev reflections peak indices reaching n = 12. Anomalous Fraunhofer patterns with missing lobes were observed in the entire range of gate voltage. We find that, by employing an fitting procedure to use the maximum entropy method in a Monte Carlo algorithm, the anomalous Fraunhofer patterns can be explained as a result of inhomogeneous supercurrent distributions on the TI surface in the junction. |
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