Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S42: Focus Session: New Topological Materials |
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Sponsoring Units: DMP Chair: Genda Gu, Brookhaven National Laboratory Room: Mile High Ballroom 4A |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S42.00001: Two-dimensional topological insulator molecular networks: dependence on structure, symmetry, and composition Liang Z. Tan, Steven G. Louie 2D molecular networks can be fabricated from a wide variety of molecular building blocks, arranged in many different configurations. Interactions between neighboring molecular building blocks result in the formation of new 2D materials. Examples of 2D organic topological insulators, that contain molecular building blocks and heavy elements arranged in a hexagonal lattice, have been recently proposed by Feng Liu and coworkers (Nano Lett., 13, 2842 (2013)). In this work, we present a systematic study of the design space of 2D molecular network topological insulators, elucidating the role of structure, symmetry, and composition of the networks. We show that the magnitude and presence of spin-orbit gaps in the electronic band structure is strongly dependent on the symmetry properties and arrangement of the individual components of the molecular lattice. We present general rules to maximize the magnitude of spin-orbit gaps and perform ab-initio calculations on promising structures derived from these guidelines. This work was supported by National Science Foundation Grant No. DMR10-1006184, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by the NSF through XSEDE resources at NICS. [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S42.00002: A large-energy-gap oxide topological insulator based on the superconductor BaBiO3 Binghai Yan, Martin Jansen, Claudia Felser Topological insulators are a new class of quantum materials that are characterized by robust topological surface states (TSSs) inside the bulk-insulating gap, which hold great po- tential for applications in quantum information and spintronics as well as thermoelectrics. One major obstacle is the relatively small size of the bulk bandgap, which is typically around 0.3eV for the known topological insulator materials. Here we demonstrate through ab initio calculations that a known superconductor BaBiO3 (BBO) with a Tc of nearly 30 K emerges as a topological insulator in the electron-doped region. BBO exhibits a large topological energy gap of 0.7 eV, inside which a Dirac type of TSSs exists. As the first oxide topological insulator, BBO is naturally sta- ble against surface oxidization and degradation, distinct from chalcogenide topological insulators. An extra advantage of BBO lies in its ability to serve as an interface between TSSs and superconductors to realize Majorana fermions for future applications in quantum computation. Reference: B. Yan, M. Jansen, C. Feler, Nature Physics (2013) doi:10.1038/nphys2762 (arXiv:1308.2303) [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S42.00003: Emergent topological phenomena in thin films of pyrochlore iridates Bohm Jung Yang, Naoto Nagaosa With the recent development of thin film and artificial superstructure growth technique, it is possible to fabricate a system, moothly connecting the two-dimensions (2D) and three-dimensions (3D). In this work we unveil the dimensional crossover of emergent topological phenomena. In particular, by focusing on the thin film of pyrochlore iridate antiferromagnets grown along the [111] direction, we demonstrate that it can show giant anomalous Hall conductance, which is as large as the Hall conductance of 3D quantum Hall insulators, even though there is no Hall effect in 3D bulk material. In addition, we show the emergence of a genuine new topological phase, dubbed the anti-Chern insulator, which is realized only in thin films. This shows that the thin film of topological materials is a new platform to search unexplored novel topological phenomena. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S42.00004: Bulk Dirac Points in Distorted Spinels Julia Steinberg, Steve Young, Saad Zaheer, Charles Kane, Eugene Mele, Andrew Rappe A Dirac point is characterized by four degenerate states that disperse linearly with momentum around a single point $bk$ in the Brillouin zone. The resulting low energy theory is pseudorelativistic. A well-known example in two dimensions is graphene, which has a Fermi surface consisting exclusively of Dirac points that are responsible for many of its exotic properties. We report on an analogous Dirac-like Fermi surface in three-dimensional bulk materials in a distorted spinel structure on the basis of density functional theory (DFT) as well as tight-binding theory. The four examples we provide in this paper are BiZnSiO$_{4}$, BiCaSiO$_{4}$, BiMgSiO$_{4}$, and BiAlInO$_{4}$. A necessary characteristic of these structures is that they contain a Bi lattice which forms a hierarchy of chain-like substructures, with consequences for both fundamental understanding and materials design. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S42.00005: Zeeman Field-``Rotated'' Transitions for Surface Chern Insulators E.J. Mele, Fan Zhang, Xiao Li, Ji Feng, C.L. Kane Mirror symmetric surfaces of a topological crystalline insulator (e.g. SnTe) host even number of Dirac surface states. A surface Zeeman field generically gaps these states leading to a quantized anomalous Hall effect. Varying the direction of Zeeman field induces transitions between different surface insulating states with any two Chern numbers between -4 and 4. In the crystal frame the phase boundaries occur for field orientations which are great circles with (111)-like normals on a sphere. [arXiv:1309.7682] [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S42.00006: Topological Phase Transition in Antimony Man-Hong Wong, Guang Bian, Caizhi Xu, Thomas Miller, Tai-Chang Chiang Spin-orbit coupling (SOC) is believed to cause the parity exchange that drives normal band insulators into the topological regime. Changing the strength of the effective SOC can also induce quantum phase transitions in materials. We performed a first-principles calculation to elucidate the quantum phase transition from a topologically trivial to nontrivial system in a 15-bilayer Sb film. We increased the k-space sampling relative to previous studies and varied the effective SOC in order to observe the changes in the bulk band gap and topological surface states. A transition from a metal to a semimetal is observed as the SOC is tuned from 0\% to 100\%. At a SOC value near 300\%, a transition from a nontrivial topological semimetal to a topological insulator occurs. Varying the effective SOC strength can be realized experimentally by alloy substitution with elements in the same column in the periodic table. Increasing the effective SOC of the Sb film to values above 100\% is a model of the Bi$_{1-x}$Sb$_{x}$ alloy, the first three-dimensional topological insulator. Further studies using this method on different systems may lead to the discovery of new topological insulators. [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:48AM |
S42.00007: Predicting Organic Topological Insulators in Organometallic Lattices Invited Speaker: Feng Liu Topological insulators (TIs) are a recently discovered class of materials having insulating bulk electronic states but conducting boundary states distinguished by nontrivial topology. So far, several generations of TIs have been theoretically predicted and experimentally confirmed, all based on inorganic materials. In this talk, I will present our recent study of a family of two-dimensional organic TIs made of organometallic lattices [1-4], based on first-principles calculations and tight-binding model analyses. Designed by assembling molecular building blocks of organometallic compounds with strong spin-orbit coupling into a hexagonal and Kagome lattices, these new classes of organic topological materials are shown to exhibit nontrivial topological edge states in both Dirac bands [1,4] and flat Chen bands (so-called fractional Chern insulator) [2,4], which are robust against significant lattice strain. Realization of half metallic state and anomalous quantum Hall effect in magnetic organic TIs with the inclusion of transition metal elements will also be discussed [3]. We envision that organic topological materials will greatly broaden the scientific scope and technological impact of emerging topological materials. \\[4pt] [1] Z. F. Wang, Zheng Liu and Feng Liu, ``Organic topological insulators in organometallic lattices,'' Nature Commun. 4, 1471 (2013).\\[0pt] [2] Z. Liu, Z. F. Wang, J.-W. Mei, Y. Wu and Feng Liu, ``Flat Chern Band in a Two-Dimensional Organometallic Framework,'' Phys. Rev. Lett. 110, 106804 (2013). \\[0pt] [3] Z. F. Wang, Z. Liu and Feng Liu, ``Quantum anomalous Hall effect in 2D organic topological insulator,'' Phys. Rev. Lett. 110, 196801 (2013). \\[0pt] [4] Z. F. Wang, N. Su and Feng Liu, ``Prediction of a Two-Dimensional Organic Topological Insulator,'' Nano Letters, 13, 2842 (2013). [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S42.00008: Probing the Topological Phase Transition via Density Oscillations in Silicene and Two-Dimensional Germanium Jianhui Zhou, Hao-Ran Chang, Hui Zhang, Yugui Yao, Di Xiao The quantum spin Hall effect (QSHE) has attracted much attention from both theoretical and experimental aspects. First principles calculations predict that low-buckled silicene and two dimensional (2D) germanium are the promising candidates for QSHE. We theoretically investigated two kinds of density oscillations: the Friedel oscillations and collective excitation in the silicene and 2D germanium within random phase approximation. We found that the tunable spin-valley constraint band structure could lead to some exotic properties in the two phenomena. Based on the exact analytical and numerical results, we demonstrated that the beating structure of screened potential as well as the undamped plasmon mode can be taken as a probe of topological phase transition from a band insulator to a topological insulator in silicene and 2D germanium. Our proposal could establish the connection between the topological phase transition and the density oscillations that can be accessed by a variety of experimental techniques. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S42.00009: Edge-states engineering of bismuth bilayer nanoribbons using first principles calculation Kyung-Hwan Jin, Seung-Hoon Jhi Study of topological insulator (TI) is recently showing remarkable progress in both theory and experiment, particularly in finding three dimensional materials. Two dimensional TI (quantum spin Hall) materials, on the other hand, have comparatively fewer examples. As such, theoretical predictions of single Bi (111) bilayers to be TI draw great attention from experiment. We investigate the edge states of quantum spin-Hall phase Bi (111) bilayer nano-ribbons (BNRs) using first-principles calculations. In contrast to the case of unsaturated atomic edges, we observe very well-defined helical edge states with linear energy dispersion when the edge atoms are passivated by chemicals such as H, NO2 or -OH. Our calculations show that the Fermi velocity and spin texture of the edge states in the BNRs is very sensitive to the kind of chemicals. We demonstrate that BNRs can be used as spin-current valves to rectify the spin-polarized electric currents via the edge states by selective passivation. Further, we examine the electronic transport properties of BNR with impurities in particular configurations. Our results provide a practical way of utilizing two-dimensional topological insulator Bi bilayer for spintronic devices. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S42.00010: Anomalous Edge Transport in the Quantum Anomalous Hall State Shou-Cheng Zhang, Jing Wang, Biao Lian, Haijun Zhang We predict by first-principles calculations that thin films of a Cr-doped (Bi,Sb)2Te3 magnetic topological insulator have gapless nonchiral edge states coexisting with the chiral edge state. Such gapless nonchiral states are not immune to backscattering, which would explain dissipative transport in the quantum anomalous Hall (QAH) state observed in this system experimentally. Here, we study the edge transport with both chiral and nonchiral states by the Landauer-Buttiker formalism and find that the longitudinal resistance is nonzero, whereas Hall resistance is quantized to h/e$^{2}$. In particular, the longitudinal resistance can be greatly reduced by adding an extra floating probe even if it is not used, while the Hall resistance remains at the quantized value. We propose several transport experiments to detect the dissipative nonchiral edge channels. These results will facilitate the realization of pure dissipationless transport of QAH states in magnetic topological insulators. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S42.00011: Large-gap Quantum Spin Hall Insulators in Tin Films Yong Xu, Binghai Yan, Hai-Jun Zhang, Jing Wang, Gang Xu, Peizhe Tang, Wenhui Duan, Shou-Cheng Zhang The search of large-gap quantum spin Hall (QSH) insulators and effective approaches to tune QSH states is important for both fundamental and practical interests. Based on first-principles calculations we find two-dimensional tin films in a honeycomb lattice, which we call ``Stanene'' structures, are QSH insulators with sizable bulk gaps of 0.3 eV, sufficiently large for practical applications at room temperature. These QSH states can be effectively tuned by chemical functionalization and by external strain. The mechanism for the QSH effect in this system is band inversion at the $\Gamma$ point, similar to the case of HgTe quantum well. Possible experimental realization of the Stanene structure will be discussed. [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S42.00012: Correlation-induced phase transitions in (111) bilayers of perovskite transition-metal oxides Satoshi Okamoto, W. Zhu, Y. Nomura, R. Arita, D. Xiao, N. Nagaosa We investigate the correlation-induced Mott, magnetic and topological phase transitions in (111) bilayers of perovskite transition-metal oxides LaAuO$_3$ and SrIrO$_3$ for which the previous density functional theory (DFT) calculations predicted topological insulating states. Using the dynamical-mean-field theory with DFT band structure and realistic Coulomb interactions, LaAuO$_3$ bilayer is shown to be far away from a Mott insulating regime, and a topological-insulating state is robust. On the other hand, SrIrO$_3$ bilayer is on the verge of an orbital-selective topological Mott transition. We also study the effect of magnetism in these systems. [Preview Abstract] |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S42.00013: Topological Insulator Proximity Effect: Emergence and Detection of Perfectly Conducting Channels Viktor Krueckl, Sven Essert, Klaus Richter We show that the proximity of a two-dimensional topological insulator can be employed to induce a channel with a perfect transmission eigenvalue hosted in the bulk of a conducting material with extended states. The perfectly conducting state inherits its topological protection from the adjacent topological insulator, and can be distinguished from a conventional edge state by its signatures in magneto transport. We present how these states are formed using band structure calculations of a model system and numerical calculations based on HgTe heterostructures. Furthermore, we propose two experimental configurations, which are able to verify the induction of a perfectly conducting channel in the localized and the diffusive regime by transport and shot noise signatures. [Preview Abstract] |
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