Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F68: Topological semimetals IFocus Recordings Available
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Sponsoring Units: DMP Chair: Ece Uykur, University of Stuttgart Room: Hyatt Regency Hotel -Hyde Park B |
Tuesday, March 15, 2022 8:00AM - 8:36AM |
F68.00001: Raman and Transient Reflectance Spectroscopy in the Type II Weyl Semimetal NbIrTe4 Invited Speaker: Leigh M Smith There has been intense interest in understanding how topological electronic structure in Weyl semimetals interact with trivial (non-topological) electron and phonon excitations. There have been a number of experimental and theoretical publications which suggest that phonons may couple strongly with the low energy topological electronic states. The van der Waals layered material NbIrTe4 is a Type II Weyl semimetal which has 8 pairs of Weyl nodes which are very close to the Fermi energy. It has broken inversion symmetry and 24 atoms per unit cell which result in 69 possible phonon modes. We use micro-Raman scattering on a single nanoflake to observe the angular polarization dependence for 19 modes with frequencies which extend from 40 to 300 cm-1. We find for the A1 symmetric phonon modes it is possible to extract directly a measure of the electron-phonon coupling and many frequencies display a strong sensitivity to only slightly different excitation energies (e.g. 2.0 eV vs 2.4 eV) . This raises the question of how one might show that a particular trivial electronic state well above the Fermi energy is strongly coupled to a low energy topological electronic excitation near the Fermi energy. I discuss very recent transient polarized reflectivity measurements at energies ranging from 0.3 to 1 eV which might show a way to answer this question. |
Tuesday, March 15, 2022 8:36AM - 8:48AM |
F68.00002: Probing the incompatibility between two superconducting condensates in proximitized type II Weyl semimetal MoTe2 devices through the disloyal edge mode Stephan Kim, Shiming Lei, Leslie M Schoop, Robert J Cava, Phuan Ong The disloyal edge mode [1] of exfoliated MoTe2 crystals with niobium (Nb) electrodes could be proximitized by either Nb or intrinsic bulk superconducting (SC) condensates. It tended to retain the memory of being proximitized by the bulk condensate, revealing the incompatibility between the two condensates. In a varying magnetic field, MoTe2 nanodevices with Nb electrodes underwent metal-SC and SC-metal transitions. The proximitized edge condensate was manifested by the modulations of critical current in differential resistance versus applied magnetic field spectra, where the areas associated with the frequencies of modulations corresponded to physical areas of samples. During the SC-metal transition, the field intervals between critical current modulations were regular, while those for the opposite transition were irregular. Cuts of such spectra at zero bias current exhibited anti-hysteretic changes of resistance during phase transitions. The differential resistance increased prematurely during the SC-metal transition, and vice versa for the opposite transition. Such observations showed that the edge mode was dominated by the bulk condensate during SC-metal transition, while it attached to the Nb condensate but interrupted by the bulk condensate during the opposite transition. |
Tuesday, March 15, 2022 8:48AM - 9:00AM |
F68.00003: Gapless electronic topology without free-electron counterpart Haoyu Hu, Silke Paschen, Lei Chen, Chandan Setty, Sarah E Grefe, Andrey Prokofiev, Stefan Kirchner, Jennifer Cano, Qimiao Si The interplay between interactions and topology in quantum materials is of extensive current interest. In noninteracting systems, electronic topology is described in terms of Bloch functions. However, strong interactions can destroy the quasi-particles and invalidate the analogy with noninteracting systems. Here, we consider a multi-channel Anderson lattice model on several lattices, where the electron correlations destroy the quasi-particles and lead to strange-metal behavior in resistivity and related properties. Space group symmetry constraints are analyzed in terms of the eigenvectors of Green's functions. We demonstrate gapless topological phases without any free-electron counterpart [1]. We characterize the electronic topology in terms of surface states and valley and spin Hall conductivities, and identify candidate materials to realize the proposed phases. Our work opens a door to a variety of gapless topological phases without free-electron counterpart in a broad range of strongly correlated metals. |
Tuesday, March 15, 2022 9:00AM - 9:12AM |
F68.00004: Observation of Unpinned 2D Dirac States in ??-Antimonene Qiangsheng Lu, Guang Bian, Jacob L Cook The discovery of graphene has stimulated enormous interest in two-dimensional (2D) electron gas with linear band structures. 2D Dirac materials possess many intriguing physical properties such as high carrier mobility and zero-energy Landau level thanks to the relativistic dispersion and chiral spin/pseudospin texture. 2D Dirac states discovered so far are exclusively pinned at high-symmetry points of the Brillouin zone, for example, surface Dirac states at Γ in topological insulators Bi2Se(Te)3 and Dirac cones at K and K′ in graphene. In this work, we report the realization of 2D Dirac states at generic k-points in ??-antimonene films with black phosphorus-like structures. These Dirac points in generic k-points are experimentally discovered for the first time, which is protected by the sublattice symmetry from gap opening in the absence of spin-orbit coupling. The unpinned nature enables a multitude of ways to control the locations of the Dirac points in momentum space. In addition, dispersions around the unpinned Dirac points exhibit intrinsically anisotropic behaviors due to the reduced symmetry of generic momentum points. These properties make the ??-antimonene films a promising platform for exploring interesting physics in unpinned 2D Dirac fermions that are distinct from the conventional Dirac states in graphene. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F68.00005: Coulomb Interactions and Renormalization of semi-Dirac fermions Valeri N Kotov, Bruno Uchoa, Taras I Lakoba We discuss Coulomb interaction effects for “type - II” semi-Dirac fermions, relevant to TiO2/VO2 heterostructures, which are Chern insulators in the presence of spin-orbital coupling. Semi-Dirac fermions of this type can be viewed as a result of three Dirac points merger. We find that at low energy there is a very strong, double logarithmic mass renormalization, which can be treated by renormalization group techniques. The result is a profound modification of the original dispersion in the quadratic direction, which at low energies becomes sub-linear with power 2/3. All physical characteristics (e.g. the density of states) are modified accordingly. Such very strong, asymptotically exact low-energy spectrum renormalization emerges as a general feature of 2D semi-Dirac systems, as it is also present for “conventional”, type - I semi-Dirac fermions, produced by merging two Dirac points. Therefore interpretation of experimental data at low temperatures has to take into account Coulomb interaction effects which for semi-Dirac fermions are much more pronounced compared to linear Dirac semimetals (such as graphene). |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F68.00006: Using Angle Resolved Photoemission Spectroscopy ARPES to unveil the Band Structure of the air stable layered ferromagnet CrxPtx-1Te2 Derek C Bergner, Warren L Huey, Luca Moreschini, Jonathan D Denlinger, Wolfgang E Windl, Alessandra Lanzara, Joshua E Goldberger, Claudia Ojeda-Aristizabal In recent years, the emergence of a long-range magnetic order in 2-D materials such as CrI3 and Cr2Ge2Te6 have created a lot of excitement. These materials are however air-sensitive, which limits possible electronic device applications. Here, we use Angle Resolved Photo Emission Spectroscopy (ARPES) to characterize an air stable layered ferromagnet CrxPtx-1Te2 synthetized by the Goldberger group at Ohio State University. [1] Previous works have identified PtTe2 as a type-II Dirac semimetal. Here, the addition of Cr forms a random alloy that brings ferromagnetism while preserving the air-stability of the transition metal dichalcogenide. We show high resolution ARPES data that make use of different light polarizations to characterize the different layered ferromagnet alloys. |
Tuesday, March 15, 2022 9:36AM - 9:48AM |
F68.00007: The low energy excitation spectrum of magic-angle semimetals Jinjing Yi The low energy excitation spectrum of a Dirac semimetal in an incommensurate potential is studied theoretically. This system possesses a magic-angle phase transition with a vanishing velocity and delocalization of plane wave eigenstates. By computing the single particle Green’s function using the kernel polynomial method we clearly demonstrate the successive formation of minibands that live on larger and larger moire’ lattices. Across the magic-angle transition we demonstrate that the imaginary part of the single particle self energy becomes non-zero comcomitant with the breakdown of the semimetallic quasiparticle excitations. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F68.00008: Discrete Quantum Geometry and Intrinsic Spin Hall Effect Jie-Xiang Yu, Jiadong Zang, Roger Lake, Yi Zhang, Gen Yin The intrinsic anomalous (spin) Hall effect originates from the topological property of the Fermi Sea, and it can be evaluated based on the integral of the Berry curvature among the occupied states. The numerical evaluation using Wannier interpolation meets a difficulty of the singularities caused by band crossings. Here, we show that the quantum geometry of the Fermi surface can be numerically described by a 3-dimensional discrete quantum manifold, which not only avoids singularities in the Fermi Sea, but also enables the precise computation of the intrinsic Hall conductivity resolved in spin, as well as any other local properties of the Fermi surface. Numerical accuracy is assured even when singularities is arbitrarily close to the Fermi level, and this method remains robust with Kramers degeneracy. We demonstrated this approach by calculating the anomalous Hall and spin Hall conductivities in a two-band model of Weyl semimetal and a full-band ab-initio model of zinc-blende GaAs. |
Tuesday, March 15, 2022 10:00AM - 10:12AM |
F68.00009: Leggett Modes in Dirac Semimetals Joseph J Cuozzo, Wenlong Yu, Paul S Davids, Tina Nenoff, Daniel B Soh, Enrico Rossi, Wei Pan Since the discovery of symmetry-broken phases hosting multiple order parameters, the condensed matter physics community has pursued control of collective modes corresponding to these order parameters. One example is a Leggett collective mode predicted more than 50 years ago. Since then, Leggett modes have been studied in multiband superconductors such as iron pnictides. However, challenges in controlling and understanding collective excitations in these complicated superconductors involving many degrees of freedom are still outstanding. Here we investigate the co-existence of surface and bulk states in a Dirac semimetal (DSM) with inter- and intraband pairing giving rise to a Leggett collective mode. We study the microwave response of a Leggett mode in a DSM-based SQUID and observe missing even Shapiro steps and a unique response to a magnetic field. We present experimental measurements of a Cd3As2-based SQUID that are consistent with the existence of a Leggett mode. |
Tuesday, March 15, 2022 10:12AM - 10:24AM |
F68.00010: Collective plasmonic modes in the chiral multifold fermionic material CoSi Barun Ghosh, Debasis Dutta, Bahadur Singh, Hsin Lin, Antonio Politano, Arun Bansil, Amit Agarwal Plasmonics in topological semimetals offers exciting opportunities for fundamental physics exploration as well as for technological applications. Here, we investigate plasmons in the exemplar chiral crystal CoSi, which hosts a variety of multifold fermionic excitations. We show that CoSi hosts two distinct plasmon modes in the infrared regime at 0.1 eV and 1.1 eV in the long-wavelength limit. The 0.1 eV plasmon is found to be highly dispersive, and originates from intraband collective oscillations associated with double spin-1 excitation, while the 1.1 eV plasmon is dispersionless and it involves interband correlations. Both plasmon modes lie outside the particle-hole continuum and possess a long lifetime. Our study indicates that the CoSi class of materials will provide an interesting materials platform for exploring fundamental and technological aspects of topological plasmonics. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F68.00011: Hidden quasi-symmetries stabilize non-trivial quantum oscillations in CoSi Chunyu Guo, Lunhui Hu, Carsten Putzke, Jonas Diaz, Xiangwei Huang, Kaustuv Manna, Feng-Ren Fan, Chandra Shekhar, Yan Sun, Claudia Felser, Chaoxing Liu, Andrei B Bernevig, Philip J Moll Unlocking the exotic properties promised to occur in topologically non-trivial semi-metals requires significant fine-tuning. The scarcity of materials in which the topological anomalies occur at the chemical potential is a major obstacle towards their applications. |
Tuesday, March 15, 2022 10:36AM - 10:48AM |
F68.00012: Weyl triplons in SrCu2(BO3) Dhiman Bhowmick We propose that Weyl triplons are expected to appear in the low energy magnetic excitations in the canonical Shastry-Sutherland compound, SrCu2(BO3)2, a quasi-2D quantum magnet. Our results show that, when a minimal, realistic interlayer coupling is added to the well-established microscopic model describing the excitation spectrum of the individual layers, the Dirac points that appear in the zero-field triplon spectrum of the 2D model split into two pairs of Weyl points along the kz direction. Varying the strength of the interlayer DM interaction and applying a small longitudinal magnetic field results in a range of band-topological transitions accompanied by changing numbers of Weyl points. We propose inelastic neutron scattering along with thermal Hall effect as the experimental techniques to detect the presence of Weyl node in the triplon spectrum of this material. We show that the logarithmic divergence in the second derivative in thermal Hall conductance near phase transition from regime Weyl points to a regime with topologically gapped bands as well as a finite slope in the thermal Hall conductance as a function of magnetic field at zero magnetic field are promising evidence for the presence of Weyl triplons. |
Tuesday, March 15, 2022 10:48AM - 11:00AM |
F68.00013: Prediction and control of the topological phases in Cs(Na, K)2Bi compound using strain-engineering Shahram Yalameha, Zahra Nourbakhsh, Ali Ramazani, Daryoosh Vashaee Design and discovery of topological quantum materials with exotic physical properties are some of the most challenging but fertile fields with revolutionary technological impacts. Topological materials such as Dirac semimetals, Weyl semimetals, and Nodal line semimetals have attracted much attention because of their unique electronic properties. However, if such materials are to underlay a technology, it is crucial to be able to control their topological phases systematically. A practical approach to control the topological phase conversion is based on strain engineering, where the symmetry and the electronic band structure can be controlled using an external stimulus. In the present work, we predict the highly stable new bialkali bismuthides compound Cs(Na,K)2Bi, that can take a diverse set of topological phases by strain-engineering. Based on first-principles studies, our findings reveal that the hydrostatic lattice compression, uniaxial compression, and uniaxial tension can transition Cs(Na,K)2Bi to a trivial semiconductor, a topological insulator, a normal insulator, a Weyl semimetal, a Dirac semimetal, and a Nodal Line semimetal. |
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