Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session Y14: Topological materials - Topology, symmetry and spin-orbit coupling |
Hide Abstracts |
Sponsoring Units: DMP Chair: Zhiqiang Mao, Tulane University Room: LACC 304B |
Friday, March 9, 2018 11:15AM - 11:27AM |
Y14.00001: Assessing Broken Inversion Symmetry in Conductive Materials Daniel Hickox-Young, James Rondinelli The coexistence of broken inversion symmetry and metallic conductivity represents a pathway to novel physics and useful properties, but the mechanisms which unite these properties remain largely unexplored. The recent discovery and synthesis of LiOsO_{3} [Shi et al., Nat. Mater. 12 (11) 1024-1027 (2013)] provides an opportunity to study noncentrosymmetric conductors in greater detail. Here we compare the lattice dynamical properties of the polar metal LiOsO_{3} with the degenerately doped ferroelectric BaTiO_{3} . We use density functional theory to investigate the interatomic force constants of both materials, providing insight into the driving forces behind the inversion symmetry-breaking structural transition. This information is coupled with the electronic and phononic structure to understand changes in off-centering driven by doping as opposed to intrinsic metallicity. |
Friday, March 9, 2018 11:27AM - 11:39AM |
Y14.00002: Band dependence of charge density wave and evidence for strong spin-orbit interaction in quasi-one-dimensional Ta_{2}NiSe_{7} Hui Xing, Jiaming He, Yiran Zhang, Libin Wen, Yueshen Wu, Yusen Yang, Hailong Lian, Shun Wang, Ying Liu, Jinyu Liu, Zhiqiang Mao Low-dimensional materials featuring charge density wave (CDW) provide opportunities for studying the effect of electron-electron interactions that depend strongly on the dimensionality. Quasi-one-dimensional transition-metal chalcogenide Ta_{2}NiSe_{7}, which crystallized in a layered monoclinic structure with ab basal plane and Ta and Ni chains along the b direction, was found to show interesting magnetoresistance (MR) originating from band dependent CDWs [1]. In this experiment, we explored further the field and field orientation dependence of MR and found a clear change in in the curvature of MR curve as a function of the field. More importantly, the magnetic field orientation dependence of MR shows a striking change of the symmetry axis below CDW transition only for a rotating magnetic field in the ac plane and current along b direction. In this configuration (H in ac plane), the symmetry axis rotates progressively when entering the CDW state and continues to rotate all the way to the lowest temperature by around 25 degrees, while for other configurations (H in bc and ab plane) the symmetry axis remains unchanged. We argue that the rotation of symmetry axis is an evidence for strong spin-orbit interaction in this system. |
Friday, March 9, 2018 11:39AM - 11:51AM |
Y14.00003: Observation of Dirac-like energy band and ring-torus Fermi surface in noncentrosymmetric pnictide CaAgAs Daichi Takane, Kosuke Nakayama, Seigo Souma, Taichi Wada, Yoshihiko Okamoto, Koshi Takenaka, Youichi Yamakawa, Ai Yamakage, Taichi Mitsuhashi, Koji Horiba, Hiroshi Kumigashira, Takashi Takahashi, Takafumi Sato Recently, hexagonal pnictides CaAgX (X= P and As) were predict to be a candidate of topological line-node semimetal with a single line node under negligible spin-orbit coupling [1]. First-principles band structure calculations suggested inverted band structure and very small spin-orbit gap for CaAgP, whereas the spin-orbit gap for CaAgAs is ~ 0.1 eV. In this presentation, we report bulk-sensitive soft x-ray ARPES measurement of CaAgAs [2]. We have established the bulk valence-band structure in 3D Brillouin zone, and observed Dirac-like energy band and ring-torus Fermi surface associated with the line node due to an intersection of bulk Ag 5s and As 4p bands at the mirror plane of the crystal. Intriguingly, we found that no other bands cross the Fermi level, thereby the low-energy excitations are solely characterized by the Dirac-like band in this material. The present result strongly suggests that CaAgX family provides an excellent platform to study interplay among line node, mirror symmetry, and exotic topological properties. |
Friday, March 9, 2018 11:51AM - 12:03PM |
Y14.00004: Thermal-driven Lifshitz Transition in layered semimetallic MoTe_{2} Dohyun Kim, Sungjong Woo, Kyungrok Kang, Min Kwon, Suyeon Cho, Jun-Ho Lee, Dongyeun Won, Byungdo Ji, Dong Hoon Keum, Young-Woo Son, Heejun Yang Electronic, thermal and mechanical (structural) properties of layered transition metal dichalcogenides (TMDC) have shown non-trivial magnetoresistance and quantum states that are promising for next-generation electronics. In particular, unsaturated magnetoresistance and superconductivity have been demonstrated and explained by the exact compensation of electrons and holes in semimetallic MoTe_{2}, which exhibits a significant temperature variation. Here, we clarify the origin of the temperature-induced non-trivial phenomena by investigating thermal expansion, band structure and phonon features of layered semimetallic MoTe_{2}. The electron and hole concentrations were found to be largely correlated with the thermal expansion properties of the material along with the role of flexural phonon in the layered material with lattice distortion. Furthermore, resistivity characteristics of the semimetallic MoTe_{2} show non-Fermi liquid behaviors. |
Friday, March 9, 2018 12:03PM - 12:15PM |
Y14.00005: Topological electronic states in spin-orbit coupled j_{eff }= 0 ground state compound Ba_{3}CaIr_{2}O_{9} Vamshi Mohan Katukuri, Quansheng Wu, Boem Hyun Kim, Oleg Yazyev Iridium oxides with d^{5} configuration have attracted considerable interest in the last decade due to the realisation of spin-orbit coupled (SOC) j_{eff} = 1/2 insulating ground states. Recently, a new class of 5d^{4} iridates with a singlet (j_{eff} = 0) ground state has been proposed and realized in Sr_{2}YIrO_{6} and Ba_{2}YIrO_{6}. Although their ground state is non-magnetic, the existence of excitonic magnetism in these materials is intensely debated. Here, we propose a new honeycomb lattice compound Ba_{3}CaIr_{2}O_{9} in the j_{eff} = 0 class of materials. Using a combination of ab initio methods including many-body wavefunction calculations we characterise the SOC ground and excited states and show that the compound realises a j_{eff} = 0 singlet state. We use a microscopic model inferred from the low energy spin-orbital states to analyse the magnetic excitations and find the system to be non-magnetic and far from being an excitonic magnetic insulator. However, we find a non-trivial electronic band structure with a well defined Z_{2} topological invariant. We analyse the effect of electronic correlations on the non-trivial bands using the Gutzwiller wavefunction approach. |
Friday, March 9, 2018 12:15PM - 12:27PM |
Y14.00006: Information Scrambling of One Dimensional Symmetry Protected Topological Phases from Thermalized Boundaries via Tensor Networks Sayonee Ray, Arpan Bhattacharyya An emerging area of study is a 1D MBL-SPT (many body localized-symmetry protected topological) bulk with a thermalized boundary which possesses a corresponding quantum anomaly characterizing the SPT bulk. The SYK model is one of them. The thermalizing and information scrambling nature of SYK has been studied from the point of view of level statistics, tripartite mutual information, out-of-time-order correlator (OTOC) etc. We aim at addressing the questions related to information scrambling of a thermalized boundary into a fermionic MBL-SPT bulk and their bulk-boundary correspondence. We consider the Kitaev Majorana wire with a SYK-like model at the boundary, with a constant strength of interaction between four Majoranas, and study the dynamics of thermalization. We aim at studying the time evolution of the GS of the boundary Hamiltonian using tensor network methods, to arrive at a bulk description consistent with the boundary. This can be generalized to SYK boundaries with random four-fermion interactions. Other possible directions of work are using a BDI-SPT bulk with thermalized boundaries like the Sherrington-Kirkpatrick model. Similar calculations for a different SPT bulk (like the AIII and CII classes) with a SYK boundary might also reveal interesting aspects. |
Friday, March 9, 2018 12:27PM - 12:39PM |
Y14.00007: Nonthermal pathway to antiferromagnetic Weyl semimetals in pyrochlore iridates Gabriel Topp, Nicolas Tancogne-Dejean, Alexander Kemper, Angel Rubio, Michael Sentef The 227 pyrochlore iridates were conjectured to exhibit an antiferromagnetically ordered Weyl semimetallic (AF-WSM) phase provided that one could tune the ordered magnetic moment. Although the equilibrium phase diagram is still under lively debate both theoretically and experimentally, no convincing evidence has been presented for the AF-WSM, and it appears that all the known compounds are antiferromagnetic insulators (AFI). Here we propose an ultrafast nonthermal pathway to engineer a nonequilibrium AF-WSM phase with short laser pulses. Motivated by Floquet-Weyl semimetallic states in non-magnetic 3D Dirac materials [1], we investigate the dynamics after an interaction quench in a mean-field dynamics simulation starting from the AFI phase. We find nonthermal magnetic phases with Weyl fermions that emerge on femtosecond time scales. Possible experimental setups to realize our proposed scheme are discussed. |
Friday, March 9, 2018 12:39PM - 12:51PM |
Y14.00008: Physical Properties of PdSb_{2} Single Crystals Ramakanta Chapai, Roshan Nepal, William Shelton, E Plummer, Rongying Jin Transition-metal dipnictide PdSb_{2} is a candidate for hosting 6-fold-degenerate exotic fermions (beyond Dirac and Weyl fermions) with degeneracy stabilized by the non-symmorphic symmetry. Such symmetry plays crucial role in electrical transport properties. We have for the first time grown single crystals of PdSb_{2} and characterized its physical properties. X-ray diffraction measurement shows that PdSb_{2} forms the Pyrite-type cubic structure (space group 205) at room temperature. Electrical resistivity displays metallic behavior with T^{2} dependence at low temperatures, indicating the Fermi-liquid ground state. The Hall coefficient is positive and decreases with increasing temperature, consistent with the multiband nature in the electronic structure. However, the transverse magnetoresistance is found to obey the Kohler’s law at all temperatures, indicating only one type (hole-type) of charge carrier dominates the electrical transport. Furthermore, we find appreciable electronic contribution on both thermal conductivity and specific heat of PdSb_{2}. The implication will be discussed based on both experimental observation and theoretical calculations. |
Friday, March 9, 2018 12:51PM - 1:03PM |
Y14.00009: Spatial Distribution of Topological Surface State Electrons in Bi_{2}Te_{3} Probed by Low Energy Na^{+} Ion Scattering Haoshan Zhu, Weimin Zhou, Jory Yarmoff Bi_{2}Te_{3} is a topological insulator (TI) whose unique properties result from topological surface states (TSS) in the band gap. The TSS are responsible for the novel spin-dependent transport properties of TI materials and their detailed characterization is needed to completely understand the relevant physics. DFT calculations suggest that the TSS electrons accumulate locally below the surface Te atoms and above the 2^{nd} layer Bi atoms, which would create upward pointing surface dipoles at the Te sites and downward pointing dipoles at the Bi sites. The neutralization probability of scattered low energy alkali ions depends on the surface local electrostatic potential (LEP) directly above the scattering site, and is thus particularly sensitive to dipoles that induce inhomogeneities in the local surface potential. It is found that the neutralization is larger when scattered from Te than from Bi, experimentally confirming the presence of the dipoles and thereby the spatial distribution of the conductive electrons in the TSS. |
Friday, March 9, 2018 1:03PM - 1:15PM |
Y14.00010: Influence of electron-phonon coupling on the pressure-induced topological phase transition in BiTeI Véronique Brousseau-Couture, Michel Cote Topological phase transitions are closely related to the bulk electronic bandstructure, which varies with temperature. This variation is a consequence of electron-phonon interactions, which induce a shift in the electronic band energies that may promote or suppress the topologically non-trivial phase. When studying tunable topological phase transitions in real materials, the value of the critical parameter may therefore change with temperature. Understanding the effect of temperature on these phase transitions is thus crucial in designing real devices intended to work in various conditions. We investigate the temperature dependence of the pressure-induced topological phase transition in three-dimensional crystalline BiTeI through first principles methods. We compute the electron-phonon coupling and the electronic bandstructure using density functional perturbation theory (DFPT). We also study the behavior of the narrow intermediate Weyl semimetal phase that has been theoretically predicted for this material, to evaluate if it could be observed experimentally. |
Friday, March 9, 2018 1:15PM - 1:27PM |
Y14.00011: Pseudo-spin internal structure for plasmons and anomalous geometric phase Li-kun Shi, Justin Song The collective plasmonic modes of two-dimensional metals comprise a simple pattern of oscillating charge density that yields enhanced light-matter interaction. Here we unveil that beneath this familiar facade, plasmons possess a hidden geometrical internal structure that fundamentally alters its dynamics. This structure comprises the local current density configuration of the electrons that form the plasmon and can take on an intricate pattern when a magnetic field is applied, exhibiting a non-trivial texture. When these plasmons scatter, their non-trivial internal structure allows them to pick up non-trivial geometric phases (tunable by hall conductivity) and can even translate its trajectory by multiple plasmon wavelengths when it is reflected off a boundary. The internal “spinor”-type structure of plasmons reveals uncharted territory for plasmonics with new ways to manipulate their trajectories, and a new playground to explore the geometry of quasiparticles. |
Friday, March 9, 2018 1:27PM - 1:39PM |
Y14.00012: Separation of topological insulator and Dirac semimetal phases in ABX honeycomb structures Xiuwen Zhang, Qihang Liu, Qiunan Xu, Xi Dai, Alex Zunger Topological insulators (TI) and Dirac semimetals (DSM) are quantum materials that have band inversion at time reversal invariant k-points. The difference is that TI has non-vanishing bulk band gap and surface Dirac cones protected by time reversal symmetry, whereas DSM has bulk Dirac cones protected by crystalline symmetry. Numerous previous theoretical studies of ABX compounds in the honeycomb lattice (space group P6_{3}/mmc) predicted many to be TIs, but the present examination of the dispersion relation in other areas of the Brillouin Zone reveals that (i) most are instead DSM (ii) We also predict a few true TI’s with good size gaps, and (iii) extending this study to hundreds of (real as well as hypothetical) ABX honeycomb structures, we separate them to be normal insulators vs metals, vs TI vs DSM. We discuss the chemical and physical rules that determine whether a band-inverted ABX honeycomb is a topological insulator or Dirac semimetal. |
Friday, March 9, 2018 1:39PM - 1:51PM |
Y14.00013: Density Response of Surface States in a Topological Crystalline Metal Jacob Gordon, Hae-Young Kee Orthorhombic perovskite iridates are predicted to realize a new class of metals called topological crystalline metals (TCMs). For particular terminations, these materials support zero energy surface states which are protected by a certain lattice symmetry. Despite experimental efforts, a direct signature of these surface states has remained elusive. Apart from difficulty in their synthesis, this is partly due to the lack of an appropriate probe which is able to distinguish between surface and metallic bulk contributions. We studied the density fluctuations of surface modes, and found that symmetry properties of the surface states allow for unique consequences for the electron-phonon interaction. Experimental implications are also discussed. |
Friday, March 9, 2018 1:51PM - 2:03PM |
Y14.00014: Universal Topological Electronic Properties of Nonmagnetic Chiral Crystals Guoqing Chang, Benjamin Wieder, Frank Schindler, Daniel Sanchez, Ilya Belopolski, Shin-Ming Huang, Bahadur Singh, Di Wu, Tay-Rong Chang, Titus Neupert, Suyang Xu, Hsin Lin, Zahid Hasan Chiral crystals are materials whose lattice structure has a well-defined handedness due to the lack of inversion, mirror, or other roto-inversion symmetries. Their structural chirality has been found to allow a wide range of phenomena, including skyrmions in chiral magnets, unconventional pairing in chiral superconductors, nonlocal transport and unique magnetoelectric effects in chiral metals. We show a universal topological electronic property of all nonmagnetic chiral crystals with spin-orbit coupling. In these materials, the combination of structural chirality and time-reversal symmetry is sufficient to guarantee the presence of two-fold-degenerate chiral fermions at the time-reversal invariant momenta, Kramers-Weyl. We further show that Kramers-Weyl fermions enable a number of unique topological phenomena, including a quantized photogalvanic current, the chiral and gyrotropic magnetic effects and electron spin-momentum locking. Considering the abundance of chiral crystals, our findings are widely applicable. The symmetry-guaranteed presence of these fermions in all chiral crystals provides a new and reliable means of engineering and controlling the unconventional optical, transport, and superconducting properties of chiral materials[1]. |
Friday, March 9, 2018 2:03PM - 2:15PM |
Y14.00015: Non-necessity of band inversion process in 2D topological insulators for bulk gapless states and topological phase transitions Wenjie Xi, Wei Ku In commonly employed models for 2D topological insulators, bulk gapless states are well known to form at the band inversion points where the degeneracy of the states is protected by symmetries. It is thus sometimes quite tempting to consider this feature, the occurrence of gapless states, a result of the band inversion process under protection of the symmetries. Similarly, the band inversion process might even be perceived as necessary to induce 2D topological phase transitions. To clarify these misleading perspectives, we propose a simple model with a flexible Chern number to demonstrate that the bulk gapless states emerge at the phase boundary of topological phase transitions, despite the absence of band inversion process. Furthermore, the bulk gapless states do not need to occur at the special $k$-points protected by symmetries. Given the significance of these fundamental conceptual issues and their wide-spread influence, our clarification should generate strong general interests and significant impacts. Furthermore, the simplicity and flexibility of our general model with an arbitrary Chern number should prove useful in a wide range of future studies of topological states of matter. |
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