Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H44: Dirac and Weyl Semimetals: Theory II |
Hide Abstracts |
Sponsoring Units: DMP Chair: Zhoushen Huang, Los Alamos National Laboratory Room: 391 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H44.00001: Van der Waals Stacking Induced Topological Phase Transition in Layered Ternary Transition Metal Chalcogenides Xiaofeng Qian Novel topological materials are key to the development of topological devices with low power consumption and heat dissipation. Here we theoretically predict that a novel class of ternary transition metal chalcogenides exhibit dual topological characteristics: quantum spin Hall insulators (QSHIs) in 2D monolayers and topological Weyl semimetals in vdW stacked noncentrosymmetric bulk. Remarkably, one can create and annihilate Weyl fermions, and realize the transition between Type-I and Type-II Weyl fermions by tuning vdW interlayer spacing, based on which we provide the missing physical picture of the evolution from 2D QSHIs to 3D Weyl semimetals. Our results show that these materials are thermodynamically stable with weak interlayer binding, implying their great potentials for experimental synthesis, characterization, and vdW heterostacking. Their ternary nature will offer more tunability for electronic structure by controlling different stoichiometry and valence charges. These new materials provide an ideal platform for exploring fundamental topological phase transition, and will open up a variety of new opportunities for 2D and topological materials research. (Reference: Junwei Liu, Hua Wang, Chen Fang, Liang Fu, and Xiaofeng Qian. arXiv preprint arXiv:1606.04522 (2016)) [Preview Abstract] |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H44.00002: Topological phases in multilayers of a Weyl semimetal and a normal insulator Kazuki Yokomizo, Shuichi Murakami We investigate multilayer systems of a normal insulator and a Weyl semimetal. We calculate the bulk band structure and determine phase diagrams by changing the thickness of the normal insulator and that of the Weyl semimetal layer using two models; one is from the effective model for a Weyl semimetal, and the other is the lattice model. We compare the results between the two models, and found that they agree well. As a result, we find that the multilayer system shows a qualitatively different behavior depending on the stacking direction relative to the displacement vector connecting between two Weyl nodes. When the stacking direction is perpendicular to the displacement vector, the Weyl semimetal and the normal insulator phases appear only. On the other hand, when it is parallel to the displacement vector, the phase diagram is rich, containing not only the Weyl semimetal phases but also the quantum anomalous Hall phases with different Chern numbers. Furthermore, the phase transition can be understood in terms of the trajectory of the Weyl nodes. [Preview Abstract] |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H44.00003: Graphene based d-character Dirac Systems Yuanchang Li, S. B. Zhang, Wenhui Duan From graphene to topological insulators, Dirac material continues to be the hot topics in condensed matter physics. So far, almost all of the theoretically predicted or experimentally observed Dirac materials are composed of $sp$-electrons. By using first-principles calculations, we find the new Dirac system of transition-metal intercalated epitaxial graphene on SiC(0001). Intrinsically different from the conventional $sp$ Dirac system, here the Dirac-fermions are dominantly contributed by the transition-metal $d$-electrons, which paves the way to incorporate correlation effect with Dirac-cone physics. Many intriguing quantum phenomena are proposed based on this system, including quantum spin Hall effect with large spin-orbital gap, quantum anomalous Hall effect, 100\% spin-polarized Dirac fermions and ferromagnet-to-topological insulator transition. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H44.00004: Topological Phases in Graphene Nanoribbons Ting Cao, Fangzhou Zhao, Steven G. Louie Using first-principles and model Hamiltonian calculations, we find that the band structures of various graphene nanoribbons give rise to interesting quantized Zak phases, depending on ribbon shape, width and edge termination. The Zak phase, an invariant of the occupied bands of the graphene nanoribbon, identifies the topological phase of the system and dictates the number of end states through the bulk-boundary correspondence. We moreover show that it can be modified by introducing an array of appropriate dopant atoms in the graphene nanoribbons. We demonstrate the origin of these findings, and connect our results to experimental measurements. [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H44.00005: Klein tunneling and magnetoresistance of \textit{p-n} junctions in Weyl semimetals Songci Li, Anton Andreev, Boris Spivak We study the zero temperature conductance and magnetoconductance of ballistic \textit{p-n} junctions in Weyl semimetals. Electron transport is mediated by Klein tunneling between \textit{n}- and \textit{p}- regions. The chiral anomaly that is realized in Weyl semimetals plays a crucial role in the magnetoconductance of the junction. With the exception of field orientations where the angle between $\mathbf{B}$ and the junction plane is small, magnetoconductance is positive and linear in $B$ at both weak and strong magnetic fields. In contrast, magnetoconductance in conventional \textit{p-n} junctions is always negative. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H44.00006: Engineering and probing topological properties of Dirac semimetal films by asymmetric charge transfer John Villanova, Edwin Barnes, Kyungwha Park Dirac semimetals (DSMs) have topologically robust three-dimensional Dirac nodes (degenerate Weyl nodes) and Fermi-arc states connecting the node projections at a surface. Recently, Na$_3$Bi and Cd$_3$As$_2$ have been experimentally confirmed to be DSMs, where the Dirac nodes are stabilized by crystal symmetries. In heterostructures involving DSMs, charge transfer occurs at the interfaces, which can be used to probe and control their bulk and surface topological properties through surface-bulk connectivity. Here we demonstrate that despite a band gap in DSM films, asymmetric charge transfer at the surface enables one to accurately identify locations of the Dirac-node projections from gapless band crossings and to examine and engineer properties of the topological Fermi-arc surface states connecting the projections, by simulating adatom-adsorbed DSM films using a first-principles method and by comparing with the effective model. We show that the amount of charge transfer changes the unique spin textures near the projections and the separation between the Fermi-arc states. Our results can be observed by top or bottom surface gating without adatoms. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H44.00007: Comparative study of Weyl semimetal and topological/Chern insulators: bulk-edge correspondence and disorder effects Ken Imura, Yukinori Yoshimura, Koji Kobayashi, Tomi Ohtsuki We report our recent study (arXiv:1606.02091) on a comparative study of the paradigmatic 3D topological phases: Weyl semimetal (WSM), strong vs. weak topological insulators (STI/WTI), and Chern insulator (CI). Regarding three-dimensional (3D) topological insulators and semimetals as a stack of constituent 2D topological (or sometimes non-topological) systems is a useful viewpoint. By calculating the Z- and Z2-indices for the thin films of such 3D topological phases, we follow dimensional evolution of topological properties from 2D to 3D. It is shown that the counterpart of STI and WTI in the time-reversal symmetry broken CI system are, respectively, WSM and CI phases. The role of bulk-edge correspondence in the STI/WTI and WSM/CI thin films will be highlighted. Transport property of disordered WSM thin films with both bulk and surface contributions is studied numerically. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H44.00008: 3D anomalous quantum Hall effect in hyperhoneycomb lattices Sang Wook Kim, Kangjun Seo, Xu Dou, Bruno Uchoa The hyperhoneycomb lattice is an example of a larger class of three dimensional structures with planar trigonally connected sites. The tight binding model of the hyperhoneycomb lattice has electronic quasiparticles around a closed nodal line, called a Dirac loop. For spineless fermions, we address the 3D anomalous quantum Hall (AQH) effect, which is expected to emerge in the corresponding lattice model through a quantum phase transition in the presence of interactions. We derive the 3D quantum Hall conductance due to surface states, and calculate a non-trivial dissipationless Hall viscosity due to elastic deformations of the lattice in the AQH regime. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H44.00009: Quantum oscillations without magnetic field in Dirac and Weyl semimetals Marcel Franz, Tianyu Liu, Dmitri Pikulin When magnetic field B is applied to a metal, nearly all observable quantities exhibit oscillations periodic in 1/B. Such quantum oscillations reflect the fundamental reorganization of electron states into Landau levels as a canonical response of the metal to the applied magnetic field. We predict here that, remarkably, in the recently discovered Dirac and Weyl semimetals quantum oscillations can occur in the complete absence of magnetic field. These zero-field quantum oscillations are driven by elastic strain which, in the space of the low-energy Dirac fermions, acts as a chiral gauge potential. We propose an experimental setup in which the strain in a thin film (or nanowire) can generate pseudomagnetic field b as large as 15T and numerically demonstrate the resulting de Haas-van Alphen and Shubnikov-de Haas oscillations periodic in 1/b. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H44.00010: Weyl nodes assisted conductivity contrast in the interfacial phase change memory Jinwoong Kim, Jeongwoo Kim, Young-Sun Song, Ruquian Wu, Seung-Hoon Jhi, Nicholas Kioussis The interfacial phase-change memory (iPCM) GeTe/Sb$_2$Te$_3$ continues to attract a great deal of interest not only because they are promising candidates for the next generation non-volatile random-access memories but also for their fascinating topological properties. Depending on the atomic-layer-stacking sequence of the GeTe block the iPCM can be either in the ``SET'' (Ge-Te-Ge-Te) or ``RESET'' (Te-Ge-Ge-Te) states where the former exhibits a ferroelectric polarization and an electric conductivity which is two orders of magnitude higher than that of the RESET state. The presence of ferroelectric polarization which breaks the inversion symmetry and the fact that the system is close to the topological phase boundary raises the intriguing question of the emergence of a Weyl semimetal phase in the ``SET'' state between the topological and trivial insulator phases as proposed by Murakami. $\it{Ab}$ $\it{initio}$ electronic structure calculations reveal the emergence of a Weyl semimetal phase for the “SET” phase associated with a large electric conductivity due to the gapless Weyl nodes. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H44.00011: Nodal-line and nodal-surface semimetals in multilayers of a topological insulator and a normal insulator Kokin Nakajin, Shuichi Murakami Phase diagram having topological insulator (TI) and normal insulator phases in multilayer of TI and insulator was reported. We introduce a multilayer, consisting of alternating layers of two type TIs and a normal insulator. We modulate the sign of the velocity of the surface Dirac corns of TI alternately. We find new phase diagram having topological nodal line semimetal (TNS) phase, which is different from a previous research. In addition, the TNS phase has nodal line and it is protected by the internal symmetry and Kramers theorem. Interestingly by breaking inversion symmetry, there appears a nodal surface in our multilayer system. Furthermore, we also discuss about the origin of the TNS phase by imposing the warping term to change system symmetry. We show that thus such multilayer exhibit various topological semimetal phases including. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H44.00012: Weyl-Majorana solenoid Maxim Breitkreiz, Paul Baireuther, Jakub Tworzydlo, Inanc Adagideli, Carlo W. J. Beenakker We investigate what happens to a Weyl semimetal wire that is covered with a superconductor. Coupling to the superconductor breaks up the Fermi arcs into pairs of Majorana modes, separated by an energy gap. Upon variation of the coupling strength along the wire there is a gap inversion that traps the Majorana fermions. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H44.00013: Magnetic Weyl Kondo semimetal phase in a topological Kondo insulator heterostructure Seulgi Ok, Ashley Cook, Titus Neupert We study a layered three-dimensional heterostructure in which two types of Kondo insulators are stacked alternatingly with different thicknesses of the individual layers. We compute the topological phase diagram of this heterostructure for a model where one of the two Kondo insulators is SmB$_6$ and the other one is YbB$_6$. Depending on the layer thickness we find a strong topological insulator, a weak topological insulator, and a trivial insulator phase. Motivated by evidence of surface ferromagnetism in SmB$_6$\footnote{Y. Nakajima, P. Syers, X. Wang, R. Wang and J. Paglione, \textit{Nature Phys.} 12, 213-217 (2016)}, we add finite magnetization along the \{001\} crystallographic direction, and characterize the electronic properties of the heterostructure as a function of YbB$_6$ layer thickness and magnetization strength. We find Weyl semimetal phases distinguished by different numbers of Weyl nodes. We explore the feasibility of experimentally realizing this magnetic Kondo Weyl semimetal by computing the bare and RPA magnetic susceptibility for the heterostructure. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H44.00014: Thin Films of New Fermion Material, Ta$_{\mathrm{3}}$Sb Mazhar Ali, See-Hun Yang, James Taylor, Stuart Parkin For the past two years, the condensed matter field has been focused on investigating Weyl fermions; one of the original three categories of Fermions predicted over 60 years ago. Recently, Bernevig et al, have shown theoretically that higher order Fermionic excitations can exist, including those coming from 3, 6, and 8 band crossings. Specifically, Ta$_{\mathrm{3}}$Sb is expected to be an example of a ``New Fermion'' material, housing 8-fold degenerate fermions near the Fermi level. In order to investigate physical properties related to this phenomenon, we have grown Ta$_{\mathrm{3}}$Sb thin films via sputtering on a variety of substrates. First results of film quality with textured films ranging from 5 to 50 nm are presented. Crystallinity was controlled via annealing as well as substrate choice. Simple heterostructures using Py and capping layers such as MgO and TaN were also created. Transport and magneto transport results on these films will also be presented. [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:30PM |
H44.00015: Universal phase diagram between spinless topological nodal-line semimetals and Weyl semimetals Ryo Okugawa, Shuichi Murakami Topological nodal-line semimetals are realizable in systems without a spin-orbit interaction when time-reversal and inversion symmetries are present. On the other hand, Weyl semimetals appear in spinless systems if either time-reversal or inversion symmetry is absent. We theoretically study a general phase transition between the topological nodal-line semimetal and Weyl semimetal phases by breaking the time-reversal or inversion symmetry. We find that the topological nodal-line semimetal necessarily transits into the Weyl semimetal by breaking time-reversal symmetry when the topological nodal line encloses a time-reversal invariant momentum. However, topological nodal-line semimetals generally become insulating by breaking inversion symmetry. Meanwhile, we show that crystallographic symmetries determine band evolutions of the topological nodal lines. As a result, gapless nodes in the topological nodal-line semimetals are protected not only by topology but also by the crystallographic symmetries in many crystals. Because of the protection of the crystal symmetries, it is shown that the spinless Weyl semimetal or nodal-line semimetal can be realized after inversion symmetry is broken. [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. |
© 2024 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
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700