Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K3: Novel Topological Materials |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Tauno Palomaki, University of Washington Room: 262 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K3.00001: Intrinsic two-dimensional organic topological insulators in metal$-$dicyanoanthracene lattices. Lizhi Zhang, Mina Yoon, Feng Liu Based on the first-principles density functional theory calculations, we identify the two-dimensional organic topological insulator (OTI) states in Cu$-$dicyanoanthracene (DCA) lattice, a system that has been grown experimentally on Cu substrate. The freestanding Cu-DCA lattice presents the $p_{z}$-orbital Kagome bands with a Dirac point at the Fermi level. Our analysis, including analysis based on a tight-binding model, the calculated Chern numbers, and the semi-infinite Dirac edge states within the spin$-$orbit coupling gaps, confirms its intrinsic topological properties. The intrinsic TI states are found to originate from a proper number of electrons filling of the hybridized bands from Cu atomic and DCA molecular orbital based on which similar lattices containing noble metal atoms (Au and Cu) and those molecules with two CN groups (DCA and cyanogens) are all predicted to be intrinsic OTIs. Our findings facilitate the future experimental confirmation of intrinsic OTIs that requires no additional doping. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K3.00002: Orbital engineering as a route towards large-gap QSH insulators Gang Li, Felix Reis, Lenart Dudy, Maximilian Bauernfeind, Stefan Glass, Werner Hanke, Ronny Thomale, Joerg Schaefer, Ralph Claessen Owing to the great potential in applications in spintronics and quantum computations, the search for quantum spin Hall (QSH) insulators with large gaps is highly desired for achieving increased operating temperatures. As initially predicted for graphene, a QSH state can, in principle, be achieved. However, the small intrinsic value and the effective second-order process of the spin-orbit coupling (SOC) in graphene limits the prospect of spin-field-effect applications. In this talk, we propose a new paradigm for QSH insulators with a large topological gap, where a substrate is not only stabilizing the quasi-2D topological insulators but, additionally, plays a pivotal role for achieving the large gap, via ``orbital engineering''. The gap is determined by the on-site, atomic SOC and not by the tiny higher-order perturbation term as in graphene. We show that this novel topological wide-gap scenario can be experimentally realized in the ``bismuthene'' system on top of the wide-gap substrate SiC(0001). A huge gap about 0.7 eV and conductive edge states are found, thus, paving the way for further fundamental studies and promising applications. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K3.00003: Nanostructured topological state in bismuth nanotube arrays: Inverting parity symmetry of molecular orbitals Kyung-Hwan Jin, Seung-Hoon Jhi, Feng Liu The topological order of a solid material is linked to its band topology of Bloch states, hence a topological material is referred to a crystalline material with long-range translational order. Consequently, so far there are only very few studies of topological phases in nanostructured materials. We demonstrate a new class of nanostructured topological materials that exhibit topological quantum phase arising from nanoscale structural motifs. Based on first-principles calculations, we show that an array of bismuth nanotubes (BiNTs), a superlattice of BiNTs with a periodicity in the order of tube diameter, behaves as a nanostructured two-dimensional (2D) quantum spin Hall (QSH) insulator, as confirmed from the calculated band topology and 1D helical edge states. The underpinning mechanism of QSH phase in the BiNT array is revealed to be inversion of parity symmetry of molecular orbitals of constituent nanostructural elements in place of atomic-orbital band inversion. The quantized edge conductance of QSH phase in BiNT array can be more easily isolated from bulk contributions and their properties can be highly tuned by tube size and chirality, representing distinctive advantages of nanostructured topological phases. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K3.00004: Strain engineering of topological edge states in MoX$_{\mathrm{2}}$ (X$=$S, Se, Te) nanoribbons with 1T' phase Ha-Jun Sung, Duk-Hyun Choe, Kee Joo Chang Two-dimensional topological insulators are known as quantum spin Hall (QSH) insulators, in which backscattering is completely forbidden for edge states. Recently, layered transition metal dichalcogenides (TMDs), MX$_{\mathrm{2}}$ (M$=$Mo, W and X$=$ S, Se, Te), with a 1T' structure have been predicted to be QSH insulators. For room-temperature operation of QSH devices without dissipation in transport, large band gaps are desired and the topological edge states should be located within the band gap. Therefore, it is interesting to see whether the topological edge states in one-dimensional nanoribbons of 1T'-MX$_{\mathrm{2}}$ actually exhibit the desired electronic properties. A further question is how the electronic structure can be modified by using an external parameter such as strain. Here we report the tunability of the topological edge states by applying strain in 1T'-MoX$_{\mathrm{2}}$ nanoribbons. The bulk gaps can reach up to 167, 228, and 362 meV under strain for X$=$ S, Se, and Te, respectively. Although the location of the Dirac point depends on the chalcogen species, we show the possibility of tuning the Dirac point in the band gap by applying compressive or tensile strain. Considering the size of band gap and the amount of strain, we suggest that MoSe$_{\mathrm{2}}$ nanoribbons would be the best candidate for QSH devices. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K3.00005: High-throughput search for topological insulators in two-dimensional materials Antimo Marrazzo, Marco Gibertini, Nicolas Mounet, Davide Campi, Nicola Marzari Topological materials are a novel class of solids with outstanding properties protected by the interplay of topology and symmetry. Some of the phenomena that can be hosted in these materials, from dissipationless electron transport to spin filtering, could be very promising for many technological applications. Nevertheless, the rarity of materials exhibiting a stable, topologically non-trivial phase at room temperature hinders development. Here, we screen a comprehensive database we recently developed of about 1800 exfoliable 2D materials, computing topological invariants from first principles (DFT-PBE with spin-orbit coupling) to search for novel topological insulators and to estimate the relative abundance of promising candidates in two dimensions. [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K3.00006: Topological Insulators sans lattices Adhip Agarwala, Vijay B. Shenoy Our understanding of topological insulators is based on an underlying lattice where the local electronic degrees of freedom at different site interact with each other in ways that produce nontrivial band topology. Indeed, the search for material systems to realize such phases have been strongly influenced by this. In this work, we show that topological insulating phases do not need a lattice. We demonstrate this by explicitly constructing models on set of sites randomly distributed in space. By studying the quantized conductances and Bott indices, we systematically show the topological character of the states in such random system in two spatial dimensions in the symmetry classes A, AII, D, DIII and C. We also demonstrate a time reversal invariant topological insulator on a random set of sites in three spatial dimensions. Our study not only provides a deeper understanding of the topological phases of non-interacting electrons, but also suggests new routes of creating them via a random distribution of impurities in an otherwise insulating host. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K3.00007: Topological Phononics and Phonon Diode Yizhou LIU, Yong XU, Shou-Cheng ZHANG, Wenhui DUAN The quantum anomalous Hall effect, an exotic topological state first theoretically predicted by Haldane and recently experimentally observed, has attracted enormous interest for low-power-consumption electronics. In this work, we demonstrated that the concept of topology can be generalized to phonons, and derived a SchrÃ¶dinger-like equation of phonons, where topology-related quantities, time reversal symmetry (TRS) and its breaking can be naturally introduced. Furthermore, we proposed a Haldane model of phonons, which gives novel quantum (anomalous) Hall-like phonon states characterized by one-way gapless edge modes within the bulk gap. The topologically nontrivial phonon states are useful not only for conducting phonons without dissipation but also for designing highly efficient phononic devices, like phonon diode, which could find important applications in future phononics. [Preview Abstract] |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K3.00008: R-DMFT analysis for reduction of topological classification in a two-dimensional weak topological insulator Tsuneya Yoshida, Norio Kawakami Recent extensive study of topological insulators and superconductors discovered the reduction of topological classification in free-fermions. By employing the real-space dynamical mean field theory, we address this issue in a two-dimensional weak topological insulator with chiral symmetry. Our analysis elucidates the following results: (a) The winding number defined by the Green's function takes a nontrivial value around the zero temperature, even when the reduction occurs. (b) The non-zero winding number and the destruction of gapless edge modes become consistent because of Mott behaviors emerging only around the edges. (c) Finite temperature effects can restore the gapless edge modes when the energy scale of the bulk gap is sufficiently larger than the interactions. [Preview Abstract] |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K3.00009: Two-dimensional topological insulators enable the fabrication of field-effect transistors with imperfect materials William Vandenberghe, Massimo Fischetti Many new two-dimensional materials such as transition-metal dichalcogenides are being researched for nanoscale field-effect transistor (FET) applications. Unfortunately, these new materials often suffer from a large concentration of defects, such as line-edge roughness, that are inevitable in the fabrication process of nanoscale devices and that degrade the performance of conventional FETs . We show how transistors made of two-dimensional topological insulator (2D TI) ribbons can operate in the presence of a large number of imperfections. In the on-state, the current flows in the topologically protected edge states and charge carriers are subject to minimal back-scattering due to imperfections. In the off-state, the current flows in bulk states in which carriers suffer from severe back-scattering due to imperfections. We obtain quantitative results for the FET performance by solving the Boltzmann equation self-consistently with the Poisson equation for different levels scattering with imperfections. We show that the 2D TI FETs exhibit a high-performance and low power consumption and therefore competitive with conventional and other proposed FET designs. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K3.00010: Quantum spin Hall phases in tin-based films on a SiC substrate: An \textit{ab initio} study. Marcelo Marques, Filipe Matusalem, Friedhelm Bechstedt, Lara Kuhl Teles The deposition of stanene overlayers on 4H-SiC(0001) substrates is studied by means of density functional theory, including van der Waals interaction, and approximate quasiparticle electronic structure calculations. The influence of the Sn overlayer geometry, the surface passivation by H and F as well as the chemical functionalization of the Sn layer by fluorine and hydrogen are investigated in detail. We computed the Z$_2$ invariant for the systems in which are Dirac cones preserved after deposition on SiC surfaces. The studied systems give rise to local minima on the total energy faces. The reactivity of the clean SiC surfaces widely destroys the band structures of freestanding stanene-like sheets, but Dirac cones and topological character survive for passivated substrate systems. Stanene-derived linear bands survive at the K point (or at the $\Gamma$ point for fluorostanene) and near the Fermi level for 2$\times$2 stanene and fluorostanene sheets on SiC 3$\times$3(0001) substrates passivated with H or F. The topological character of stanene and fluorostanene, as quantum spin Hall phase, is preserved, when the SiC substrate is passivated, as indicated by $Z_2=1$. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K3.00011: Novel Quantum Spin-quantum Anomalous Hall Effect with Tunable Edge States in Sb Monolayer-based Materials Tong Zhou, Hua Jiang, Zhongqin Yang A novel quantum spin-quantum anomalous Hall (QSQAH) effect, where the quantum anomalous Hall effect (QAH) occurs at one valley and the quantum spin Hall effect (QSH) occurs at the other valley, is predicted in Sb monolayer-based materials by using \textit{ab initio} methods. The non-magnetic and magnetic atoms induce a drastic staggered exchange field, which together with proper spin-orbit coupling (SOC) interactions from Sb $p_{x}$ and $p_{y}$ orbitals, generates the QSQAH effect in the system. A tight-binding model based on $p_{x}$ and $p_{y}$ orbitals is constructed to understand the underlying physical mechanism of the QSQAH effect. Dissipationless chiral charge edge states related to one valley are found to emerge along the both sides of the sample, while low-dissipation spin edge states related to the other valley flow only along one side of the sample. These edge states can be tuned flexibly by polarization-sensitive photoluminescence controls and/or chemical edge modifications. Such flexible manipulations of the charge, spin, and valley degrees of freedom provide a promising route towards applications in electronics, spintronics, and valleytronics. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K3.00012: Observation of thickness-dependent topological phase transition in Sb films chenhui yan, Mingxing Chen, Michael Weinert, Lian Li Topological insulators are distinguished by their metallic boundary states, and topological phase transitions that can be tuned between trivial and nontrivial by several parameters, such as composition, strain, and electrical field. Here we demonstrate such phase transition by fine tuning the thickness of Sb films prepared by molecular beam epitaxy. Based on in situ STM observations, we find that Sb growth on 3D topological insulator Sb2Te3(111) initiates at step edges, leading to islands with various heights. Spatially resolved tunneling spectroscopy measurements reveal edge states for Sb films 4-8 bilayer thick, which are absent for 2 and 10 bilayer films. The edge states are confined within a few lattice spacing (1.5-2nm) from the step edge. Supported by density functional theory calculations, our findings indicate Sb(111) films undergo a phase transition from normal insulator to two-dimensional topological insulator at a critical thickness of 3 bilayers. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K3.00013: Scanning Tunneling Spectroscopy of 2D Topological Insulators Joshua Kahn, Paul Nguyen, Bosong Sun, Tauno Palomaki, Jiun-Haw Chu, David Cobden 2D topological insulators (TIs) are an exciting new class of material, wherein band inversion in the bulk leads to topologically protected gapless edge modes. In WTe$_{2}$ and ZrTe$_{5}$, two potential 2D TIs we are studying, these edge modes are confined to within tens of nanometers of the edge of the sample. Scanning tunneling spectroscopy (STS) should provide a powerful probe of these modes, and open opportunities to study the effects of gating and proximity effect due to layered superconductors, such as NbSe$_{2}$ and FeSeTe, in contact with the 2D TIs. However, these measurements require extremely clean surfaces and interfaces, protection of these sensitive materials from oxidation, and the ability to position the tip accurately on the substrate. To satisfy these requirements and allow STS, we must prepare everything away from air and encapsulate in monolayer hBN. We present our progress in developing these techniques, and some preliminary measurements. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K3.00014: STM/S study of edge states in a large energy gap near the step edges on the surface of ZrTe$_{\mathrm{5}}$ Rui Wu, Xiong Huang, Ruizhe Liu, Jiaxin Yin, Junzhang Ma, Simin Nie, Lingxiao Zhao, Bingbing Fu, Pierre Richard, Genfu Chen, Zhong Fang, Xi Dai, Hongming Weng, Tian Qian, Hong Ding, Shuheng Pan Despite considerable theoretical efforts in predicting large-gap two-dimensional topological insulator candidates, none of them have been experimentally demonstrated to have a full gap, which is crucial for quantum spin Hall effect. Here, we use low temperature scanning tunneling microscopy/spectroscopy (STM/S) to study the single crystal of ZrTe$_{\mathrm{5}}$, which has a qusi-2D layered structure and is a potential large-gap 2D TI predicted by calculations. The results reveal that ZrTe$_{\mathrm{5}}$ hosts a large full energy gap of \textasciitilde 100 meV on the surface and a nearly constant density of states within the entire gap at the monolayer step edge. These features are well reproduced by our first-principles calculations, which point to the topologically nontrivial nature of the edge states. The gap position in Brillouin zone and the band structure are demonstrated by angle-resolved photoemission spectroscopy. We also make a study for HfTe$_{\mathrm{5\thinspace }}$by using STM/S, which confirms the same behaviors as on ZrTe$_{\mathrm{5}}$. [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K3.00015: Realization of Bismuthene --- A Novel High-Tem-perature Quantum Spin Hall Candidate Joerg Schaefer, Felix Reis, Gang Li, Lenart Dudy, Maximilian Bauernfeind, Stefan Glass, Werner Hanke, Ronny Thomale, Ralph Claessen Quantum spin Hall materials promise revolutionary devices based on dissipationless spin currents in conducting edge channels. However, for current systems such as HgTe the decisive bottleneck preventing applications is the small bulk energy gap of less than 30 meV, requiring cryogenic operation temperatures. In our current study combining experiment and theory we demonstrate that the room-temperature regime, manifest in a large bulk energy gap, can be achieved by a new quantum spin Hall paradigm. In contrast to the previous mechanisms at work in graphene and HgTe, respectively, our approach specifically exploits the on-site atomic spin-orbit coupling as a third avenue. It is based on a substrate-supported monolayer of the high-Z element bismuth, and is experimentally realized as a honeycomb lattice of ``bismuthene'' on top of the insulator SiC(0001). Consistent with theory, we detect a huge bulk gap of $\sim$0.8 eV and conductive edge states [1]. Our results demonstrate a concept for a quantum spin Hall wide-gap scenario, where the chemical potential resides in the global system gap, ensuring robust edge conductance. \newline [1] F. Reis \textit{et al.}, arXiv:1608.00812 [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