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

Hide Abstracts 
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 NbIrTe_{4} Invited Speaker: Leigh M Smith There has been intense interest in understanding how topological electronic structure in Weyl semimetals interact with trivial (nontopological) 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 NbIrTe_{4} 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 microRaman 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 A_{1} symmetric phonon modes it is possible to extract directly a measure of the electronphonon 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 metalSC and SCmetal 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 SCmetal 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 antihysteretic changes of resistance during phase transitions. The differential resistance increased prematurely during the SCmetal transition, and vice versa for the opposite transition. Such observations showed that the edge mode was dominated by the bulk condensate during SCmetal 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 freeelectron 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 quasiparticles and invalidate the analogy with noninteracting systems. Here, we consider a multichannel Anderson lattice model on several lattices, where the electron correlations destroy the quasiparticles and lead to strangemetal 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 freeelectron 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 freeelectron 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 twodimensional (2D) electron gas with linear band structures. 2D Dirac materials possess many intriguing physical properties such as high carrier mobility and zeroenergy Landau level thanks to the relativistic dispersion and chiral spin/pseudospin texture. 2D Dirac states discovered so far are exclusively pinned at highsymmetry points of the Brillouin zone, for example, surface Dirac states at Γ in topological insulators Bi_{2}Se(Te)_{3} and Dirac cones at K and K′ in graphene. In this work, we report the realization of 2D Dirac states at generic kpoints in ??antimonene films with black phosphoruslike structures. These Dirac points in generic kpoints are experimentally discovered for the first time, which is protected by the sublattice symmetry from gap opening in the absence of spinorbit 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 semiDirac fermions Valeri N Kotov, Bruno Uchoa, Taras I Lakoba We discuss Coulomb interaction effects for “type  II” semiDirac fermions, relevant to TiO_{2}/VO_{2} heterostructures, which are Chern insulators in the presence of spinorbital coupling. SemiDirac 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 sublinear with power 2/3. All physical characteristics (e.g. the density of states) are modified accordingly. Such very strong, asymptotically exact lowenergy spectrum renormalization emerges as a general feature of 2D semiDirac systems, as it is also present for “conventional”, type  I semiDirac 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 semiDirac 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 Cr_{x}Pt_{x1}Te2 Derek C Bergner, Warren L Huey, Luca Moreschini, Jonathan D Denlinger, Wolfgang E Windl, Alessandra Lanzara, Joshua E Goldberger, Claudia OjedaAristizabal In recent years, the emergence of a longrange magnetic order in 2D materials such as CrI3 and Cr2Ge2Te6 have created a lot of excitement. These materials are however airsensitive, which limits possible electronic device applications. Here, we use Angle Resolved Photo Emission Spectroscopy (ARPES) to characterize an air stable layered ferromagnet Cr_{x}Pt_{x1}Te2 synthetized by the Goldberger group at Ohio State University. [1] Previous works have identified PtTe2 as a typeII Dirac semimetal. Here, the addition of Cr forms a random alloy that brings ferromagnetism while preserving the airstability 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 magicangle semimetals Jinjing Yi The low energy excitation spectrum of a Dirac semimetal in an incommensurate potential is studied theoretically. This system possesses a magicangle 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 magicangle transition we demonstrate that the imaginary part of the single particle self energy becomes nonzero 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 JieXiang 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 3dimensional 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 twoband model of Weyl semimetal and a fullband abinitio model of zincblende 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 symmetrybroken 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 coexistence 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 DSMbased SQUID and observe missing even Shapiro steps and a unique response to a magnetic field. We present experimental measurements of a Cd3As2based 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 longwavelength limit. The 0.1 eV plasmon is found to be highly dispersive, and originates from intraband collective oscillations associated with double spin1 excitation, while the 1.1 eV plasmon is dispersionless and it involves interband correlations. Both plasmon modes lie outside the particlehole 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 quasisymmetries stabilize nontrivial quantum oscillations in CoSi Chunyu Guo, Lunhui Hu, Carsten Putzke, Jonas Diaz, Xiangwei Huang, Kaustuv Manna, FengRen Fan, Chandra Shekhar, Yan Sun, Claudia Felser, Chaoxing Liu, Andrei B Bernevig, Philip J Moll Unlocking the exotic properties promised to occur in topologically nontrivial semimetals requires significant finetuning. 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 ShastrySutherland compound, SrCu2(BO3)2, a quasi2D quantum magnet. Our results show that, when a minimal, realistic interlayer coupling is added to the wellestablished microscopic model describing the excitation spectrum of the individual layers, the Dirac points that appear in the zerofield 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 bandtopological 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)_{2}Bi compound using strainengineering 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)_{2}Bi, that can take a diverse set of topological phases by strainengineering. Based on firstprinciples studies, our findings reveal that the hydrostatic lattice compression, uniaxial compression, and uniaxial tension can transition Cs(Na,K)_{2}Bi to a trivial semiconductor, a topological insulator, a normal insulator, a Weyl semimetal, a Dirac semimetal, and a Nodal Line semimetal. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700