Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W43: Topological Insulators: New Materials Predictions |
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Sponsoring Units: DCMP Chair: Nuh Gedik, Massachusetts Institute of Technology Room: Mile High Ballroom 4B |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W43.00001: A DFT study of supported 2D-Sn (Stannanane) films Ana Suarez Negreira, Max Fischetti Theoretical studies indicated that Sn monolayer is a 2D topological insulator with robust properties against small perturbations, thus resulting in large tolerance against variations induced by a manufacturing process. The downside of many topological properties is that they manifest themselves only at very low temperatures. However, thin film of Sn have a significantly higher phase transition temperature, up to 120 $^{\circ}$C, creating new opportunities of using this material in nano-electronics applications. Since stannanane has never been synthesized before, its existence and mechanical stability are open questions. Using density functional theory (DFT), we study the growth of stannanane on various substrates (i.e., InSb(100) and CdTe(100)). The impact of the substrate on the electronic properties of this topological insulator is studied through Bader charge and density of states (DOS) analyses. Finally, ab initio thermodynamics methodology is used to study the stability of different Sn surface terminations as a function of temperature and pressure. [Preview Abstract] |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W43.00002: Giant topological insulator gap and Rashba splitting in honeycomb Pb Haiyan He, Jun Hu, Ruqian Wu It was predicted that graphene can be a topological insulator (TI) due to its special Dirac states and spin-orbit coupling (SOC). However, the SOC gap of pure graphene is too small for experimental observation. It was found that heavier group IV elements, such as Si and Ge, can also produce the TI state in the tow-dimensional honeycomb lattice, with their SOC gaps a few orders larger than that of graphene. In the present work, we find that the honeycomb Pb is also a TI, with a SOC gap as large as 250 meV. We demonstrate the feasibility of making a honeycomb Pb monolayer on the Al$_2$O$_3$(0001) substrate. Moreover, Pb/Al$_2$O$_3$(0001) has a giant Rashba splitting of 270 meV, useful for spintronics and topotronics applications. [Preview Abstract] |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W43.00003: Prediction of a Two-Dimensional Organic Topological Insulator Zhengfei Wang, Ninghai Su, Feng Liu Topological insulators (TI) are a class of materials exhibiting unique quantum transport properties with potential applications in spintronics and quantum computing. To date, all of the experimentally confirmed TIs are inorganic materials. Recent theories predicted the possible existence of organic TIs (OTI) in two-dimensional (2D) organometallic frameworks. However, those theoretically proposed structures do not naturally exist and remain to be made in experiments. Here, we identify a recently experimentally made 2D organometallic framework, consisting of $\pi $-conjugated nickel-bis-dithiolene with a chemical formula Ni$_{\mathrm{3}}$C$_{\mathrm{12}}$S$_{\mathrm{12}}$, which exhibits nontrivial topological states in both a Dirac band and a flat band, therefore confirming the existence of OTI. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W43.00004: Topological phase transition driven by electron-phonon interaction Kush Saha, Ion Garate We study the effect of electron-phonon interactions in the band topology of Dirac insulators, both at zero and finite temperature. Elaborating on recent theoretical work [1], we determine how and when phonons can drive a trivial insulator into a topological insulating phase. As an application, we evaluate the temperature-dependence of the critical thickness for the topological transition in CdTe/HgTe quantum wells. \\ \\ Ref[1]: Ion Garate, PRL 110, 046402 (2013). [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W43.00005: Topological effects in an electric-field-driven hexagonal lattice Woo-Ram Lee, Kwon Park In this work, using the Floquet theory, we investigate the topological effects in a hexagonal lattice under the influence of in-plane electric field. It is found that the Bloch oscillation of an electron in a hexagonal lattice causes topologically nontrivial energy shift in Wannier-Stark energy ladders, depending on the strength and relative angle of the electric field. Importantly, the energy shift is connected to the Berry curvature effect, which induces Hall current. In the presence of spin-orbit coupling, the competition between the electric field and the spin-orbit coupling is also studied. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W43.00006: Weak Topological Insulators in PbTe/SnTe superlattice Gang Yang, Junwei Liu, Liang Fu, Wenhui Duan, Chaoxing Liu It is desirable to realize topological phases in artificial structures by engineering electronic band structures. In this paper, we investigate (PbTe)$_m$(SnTe)$_{2n-m}$ superlattices along the [001] direction and find a robust weak topological insulator phase for a large variety of layer numbers $m$ and $2n-m$. We confirm this topologically non-trivial phase by calculating $Z_2$ topological invariants and topological surface states based on the first-principles calculations. We show that the folding of Brillouin zone due to the superlattice structure plays an essential role in inducing topologically non-trivial phases in this system. This mechanism can be generalized to other systems in which band inversion occurs at multiple momenta, and gives us a brand-new way to engineer topological materials in artificial structures. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W43.00007: Numerical Study of a Bosonic Topological Insulator in three dimensions Scott Geraedts, Olexei Motrunich We construct a model which realizes a (3+1)-dimensional symmetry-protected topological phase of bosons with $U(1)$ charge conservation and time reversal symmetry, envisioned by A. Vishwanath and T. Senthil [PRX 4 011016]. Our model works by introducing an additional $O(3)$ degree of freedom, and binding its hedgehogs to a species of charged bosons; the continuous symmetry is thus enlarged to $SO(3)\times U(1)$. We study the model using Monte Carlo and determine its bulk phase diagram; the phase where the bound states of hedgehogs and charges condense is the topological phase. We also study surface phase diagram on a (2+1)-dimensional boundary between the topological and trivial insulators. The theory for the surface is the same as for a (2+1)D hedgehog-suppressed non-linear sigma model, which confirms the proposed so-called NCCP$^1$ field theory. We apply a Zeeman field to the surface, which breaks time reversal on the surface only, and observe a surface Hall conductivity which is half of a quantized value allowed for bosons in strictly (2+1)D, thus establishing topological nature of the (3+1)D bulk phase. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W43.00008: Wannier Center Sheets in Topological Insulators Maryam Taherinejad, Kevin Garrity, David Vanderbilt The electronic ground state in a periodic crystalline insulator can be described by hybrid Wannier functions $\vert W_{nl_z}(k_x,k_y)\rangle$ which are maximally localized in one direction and Bloch-like in the other two. In 3D insulators the Wannier charge centers (WCCs), defined as $\bar{z}_n(k_x,k_y)=\langle W_{n0}(k_x,k_y) \vert \hat{z} \vert W_{n0}(k_x,k_y)\rangle$, are functions of momentum in two dimensions and can be plotted as sheets over the 2D Brillouin zone. We show that the symmetry group of the WCCs $\bar{z}_n(k_x,k_y)$ includes all the symmetries of surface energy bands $\epsilon_n(k_x,k_y)$. More importantly, the WCCs contain the same kind of topological information as is carried in the surface energy bands, with the crucial advantage that the topological properties of the bulk can be deduced from bulk properties alone. The distinct topological behavior of these WCC sheets in trivial, Chern, weak, strong, and crystalline topological insulators are demonstrated using different tight-binding models. The WCC sheets calculated from first-principles calculations in $Z_2$-even Sb$_2$Se$_3$, weak $Z_2$-odd KHgSb, and strong $Z_2$-odd Bi$_2$Se$_3$ confirm the results from the tight-binding models. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W43.00009: Localization and topology protected quantum coherence at the edge of `hot' matter Yasaman Bahri, Ronen Vosk, Ehud Altman, Ashvin Vishwanath Topological phases are often characterized by special edge states confined near the boundaries by an energy gap in the bulk. On raising temperature, these edge states are lost in a clean system due to mobile thermal excitations. Recently, however, it has been established that disorder can localize an isolated many-body system, potentially allowing for a sharply defined topological phase even in a highly excited state. Here we show this to be the case for the topological phase of a one-dimensional magnet with quenched disorder which features spin one-half excitations at the edges. The time evolution of a simple, highly excited initial state is used to reveal quantum coherent edge spins. In particular, we demonstrate, using theoretical arguments and numerical simulation, the coherent revival of an edge spin over a time scale that grows exponentially larger with system size. This is in sharp contrast to the general expectation that quantum bits strongly coupled to a `hot' many body system will rapidly lose coherence. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W43.00010: Floquet Topological Insulators in Uranium Compounds Shu-Ting Pi, Sergey Savrasov A major issue regarding the Uranium based nuclear fuels is to conduct the heat from the core area to its outer area. Unfortunately, those materials are notorious for their extremely low thermal conductivity due to the phonon-dominated-heat-transport properties in insulating states. Although metallic Uranium compounds are helpful in increasing the thermal conductivity, their low melting point still make those efforts in vain. In this report, we will figure out potential Uranium based Floquet topological insulators where the insulating bulk states accompanied with metallic surface states is achieved by applying periodic electrical fields which makes the coexistence of both benefits possible. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W43.00011: Broadband spectroscopic characterization of topological crystalline insulator Pb$_{0.77}$Sn$_{0.23}$Se Anjan Reijnders, Jason Hamilton, Quinn D. Gibson, Robert J. Cava, Kenneth S. Burch Topological crystalline insulators (TCI) are novel materials in which mirror symmetry protects the presence of spin polarized surface states. In this talk I will present the temperature dependent optical properties of Pb$_{0.77}$Sn$_{0.23}$Se, a compound with a temperature dependent trivial to nontrivial topological phase transition. Reflectance and ellipsometry data between 6 meV - 5.95 eV will be discussed in conjunction with optical conductivity and the frequency dependent scattering rate, revealing hints of the topological phase transition. [Preview Abstract] |
Thursday, March 6, 2014 4:42PM - 4:54PM |
W43.00012: Properties of 2D Chiral Tensor Network States Barry Bradlyn, Jerome Dubail, Nicholas Read States that can be represented as a sum over local auxiliary degress of freedom are known as tensor network states (TNSs) [1]. In a recent paper [2], Dubail and Read gave a construction for free fermion TNSs in the chiral $p+ip$ and $\nu=1$ Chern insulator topological phases in two dimensions, and gave a generalization to Laughlin-like states. However, on general principles these free fermion states must be ground states of gapless local Hamiltonians. In this talk, we address the issue of what topological properties persist in these gapless states. We show analytically that the DC Hall conductivity for the $\nu=1$ Chern insulator TNS is quantized, although the conductivity tensor at finite frequency suffers from non-analytic corrections. Additionally, we investigate the issue of the energy gap for the interacting $\nu=1/2$ Laughlin-like TNS through Monte Carlo simulations.\\ \\ {\bf References} \\ $[1]$ F. Verstraete and J.I. Cirac, cond-mat/0407066 (2004).\\ $[2]$ J. Dubail and N. Read, arXiv:1307.7726 (2013). [Preview Abstract] |
Thursday, March 6, 2014 4:54PM - 5:06PM |
W43.00013: Localized electron basis sets and the electronic properties of novel materials Pablo Rivero, Victor Manuel Garcia-Suarez, Jaime Ferrer, Kyungwha Park, Salvador Barraza-Lopez Density functional theory algorithms based on localized electron basis sets permit calculation of material properties with modest computational cost, provided quantitative benchmarks against known properties available. Within the SIESTA computational package, we present a pragmatic and quantitative method to optimize basis sets and pseudopotentials of ordinary and novel materials. The method gives us a solid foundation to explore the electronic properties of new materials such as the strong topological insulator Bi$_{2}$Se$_{3}$. [Preview Abstract] |
Thursday, March 6, 2014 5:06PM - 5:18PM |
W43.00014: Solitons, charge fractionization, and the emergence of topological insulators in graphene rings Constantine Yannouleas, Igor Romanovsky, Uzi Landman The doubly-connected polygonal geometry of planar graphene rings is found to bring forth topological configurations for accessing nontrivial relativistic quantum field (RQF) theory models that carry beyond the constant-mass Dirac-fermion theory. These include generation of sign-alternating masses, solitonic excitations, and charge fractionization. The work integrates a RQF Lagrangian formulation with numerical tight-binding Aharonov-Bohm electronic spectra and the generalized position-dependent-mass Dirac equation. In contrast to armchair graphene rings (aGRGs) with pure metallic arms,\footnote{% I. Romanovsky, C. Yannouleas, and U. Landman, Phys. Rev. B {\bf 87}, 165431 (2013)} certain classes of aGRGs with semiconducting arms, as well as with mixed metallic-semiconducting ones, are shown to exhibit properties of one-dimensional nontrivial topological insulators. This further reveals an alternative direction for realizing a graphene-based nontrivial topological insulator through the manipulation of the honeycomb lattice geometry, without a spin-orbit contribution. [Preview Abstract] |
Thursday, March 6, 2014 5:18PM - 5:30PM |
W43.00015: Topological magnetic crystalline insulators and co-representation theory Ruixing Zhang, Chaoxing Liu We introduce a new type of topological insulator protected by magnetic group symmetry, which is a combined symmetry of point group symmetry and time reversal symmetry. Based on the Herring rule of the co-representation theory of magnetic group, we systematically show that systems with certain magnetic group symmetries can have Kramers'-like degeneracies and admit a Z2 classification. We establish a tight-binding model describing a layered magnetic structure with combined C4 rotation and time reversal symmetry. We show that this model can support non-trivial topological phases by calculating its gapless surface states and defining its Z2 topological invariant. [Preview Abstract] |
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