Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session AAA09: V: Topological Phenomena IIFocus
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Sponsoring Units: DMP Chair: Saravana Prakash Thirumuruganandham, Centro de Investigación de Ciencias Humanas y de la Educació Room: Virtual Room 9 |
Wednesday, March 22, 2023 12:30PM - 1:06PM |
AAA09.00001: The classification and diagnosis of magnetic topological states Invited Speaker: Chen Fang Topological band theory, essentially single-particle, can be extended to magnetic materials, as long as we assume that the electrons that contribute to topology are separate from those that contribute to local moments, which are static, and that the electrons interact with the local moments only via exchange coupling (effective Zeeman). When these assumptions hold, the topological classification of magnetic insulators reduces to that of non-interacting fermions protected by magnetic space groups. In this talk, I first review a general method called the "real-space recipes" for exhaustively constructing all gapped topological states protected by spatial symmetries. Then I apply this method to the case of magnetic space groups, obtaining a full classification of magnetic topological insulators in 3D. Finally, I briefly discuss a new type of symmetry, the spin-space groups, and their representations. The study of spin-space groups has been recently revived due to the experimental advances in altermagnetism. |
Wednesday, March 22, 2023 1:06PM - 1:18PM |
AAA09.00002: Theory of Emergent Inductance and Capacitance in Topological Insulator Thin Films. Stewart E Barnes The theory of emergent inductance in magnetic materials is based upon the modification of Faraday's law of electromagntic inducance proposedby Barnes and Maekawa in the context of spin-motive forces (SMF). Descrbed will be a theory of emergent inductance of the surface state of a nominally non-magnetic two dimensional topolocical insulator (TI). The reality of emergent inductance is over a hunderd years old with a quartz crystal being the classical example. Such a crystal is voltage driven and corersponds to an emergent series LCR circuit implying that a quatrz crystal is not a useful inductance at low frequency. In contrast the current driven magnetic and topological systems represent a parallel LCR circuit. An emergent L is always accompanied by a C and losses by an R. The SMF and equivent LCR circuit of a TI require the evalaution of the spin off-diagonal Berrry connection As. It is exciting that experiment on such equivalent LCR circuits represents a significant critical illustration of spin Berry phase phyics. It is found the observed would be negative L values observed experimentally in magnets reflects the effect of the C of a parallel LCR circuit with appropriate parameters. A number of experimental predictions will be made. |
Wednesday, March 22, 2023 1:18PM - 1:30PM |
AAA09.00003: Anomalous Hall effect in conical helimagnet crystals Yuri Dahnovsky Spin-spiral texture can substantially change charge transport properties in helimagnets. We find the anomalous Hall effect (AHE) exhibiting the dramatic behavior with respect to chemical potential, μ, in conical magnetic structures. The direct conductivity demonstrates kinks, and the Hall current exhibits minima and maxima changing the direction. We analytically derive the expression for energy bands and eigenstates for the most general case. Because of the conical potential, the energy bands are split into two nonparabolic bands where the lower band can have one- or two-minima shapes in the kz-direction (z is a direction of the spiral axis). We prove that the origin of the anomalous Hall effect is not topological and is due to the anisotropy of the energy bands resulting from the conical potential. We also investigate the dependence of transport properties on conical angle, $ heta$, and find that the effects are most pronounced at θ = π/2 (a helical state). Electric current is calculated using the Boltzmann equation where the relaxation is caused by electron-acoustic phonon interaction. The transition probability is a 2×2 matrix with nonvanishing off-diagonal elements indicating the strong interband transitions. The origin of interband transitions is because of the nature of the conical potential where conduction electron spins interact with localized magnetic moments. To verify the proposed theory, we calculate the temperature dependence of resistivity for MnSe and MnP crystals and find the discontinuity at the phase transition between conical and paramagnetic phases. The calculations are in the excellent agreement with the experimental data. In addition, we predict the discontinuity behavior for the anomalous Hall resistivity at the phase transition where the resistivity drops to zero in the paramagnetic phase at T = TC. |
Wednesday, March 22, 2023 1:30PM - 1:42PM |
AAA09.00004: First Principles Calculations of a Topological Invariant for Thin Magnetically-Doped SnTe Keith G Ray, Dongxia Qu Harnessing quantum anomalous hall effect materials for applications often requires insulating properties in the bulk. In thin films, bulk conductivity can be affected by surface termination and strain induced by the substrate. Furthermore, interactions between the top and bottom surfaces may alter the band topology of the material and therefore the Chern number of the quantum anomalous hall state. To assess these effects, we performed density functional theory calculations of the electronic structure for SnTe thin films with differing thickness, strain, surface termination, and Cr-doping. We also calculated the Chern number for these cases. We found that certain surface terminations allow for the multiple gapped Dirac cones of SnTe to align, creating a common insulating gap. Furthermore, magnetism through Cr-doping is calculated to produce a non-zero Chern number. |
Wednesday, March 22, 2023 1:42PM - 1:54PM |
AAA09.00005: CP2 Skyrmion and Skyrmion Crystals in Realistic Quantum Magnets Hao Zhang, Zhentao Wang, David Dahlbom, Kipton M Barros, Cristian Batista Magnetic skyrmions are nanoscale topological textures recently observed in different families of quantum magnets. These textures are called CP1 skyrmions because the target manifold of the magnetization field is the 2D sphere S2≅CP1. In this work, we will generalize the concept of magnetic skyrmions by exploiting the fact that N-level systems admit more than one classical limit. Here we report the emergence of magnetic CP2 skyrmions in realistic spin-1 models based on SU(3) coherent states. Moreover, unlike CP1 skyrmions, CP2 skyrmions can also arise as metastable textures of quantum paramagnets, opening a new road to discover emergent topological solitons in non-magnetic materials. |
Wednesday, March 22, 2023 1:54PM - 2:06PM |
AAA09.00006: Spin polarized Majorana zero modes in penta-silicene nanoribbons Marcos Sergio Figueira S Silva, Renan Bento R Campos, Jorge H Correa, Luciano S Ricco, Ivan A Shelykh, Mucio A Continentino, Antonio C Seridonio, Guy L Lay In the present work, we study the possibility of obtaining Majorana zero modes (MZMs) in penta-silicene nanoribbons (p-SINRs) [R. Pawlak et al. Proceedings of the National Academy of Sciences 117, 228 (2020)], following the same procedure as our previous work [R. C. Bento Ribeiro et al. Phys. Rev. B 105, 205115 (2022)]. The spinless and spin full p-SINR with p-wave superconducting pairing reveals the emergence of topologically protected MZMs at opposite edges of the p-SINR. We consider an external magnetic field perpendicularly applied to the nanoribbon plane and an extrinsic Rashba spin-orbit coupling (RSOC), besides the first nearest neighbor hopping term and p-wave superconducting pairing. The dispersion relation profiles show the closing and reopening of the superconducting gap for only one spin component, suggesting a spin-polarized topological phase transition (TPT). Associated with these TPTs, the energy spectrum as a function of the p-SINR chemical potential exhibits zero-energy states and preferential spin direction. It is associated with nonoverlapping wave functions well-localized at opposite edges of the superconducting p-SINR. Our findings strongly suggest the emergence of topologically protected and spin-polarized MZMs at the p-SINR ends. |
Wednesday, March 22, 2023 2:06PM - 2:18PM |
AAA09.00007: Chiral detection of Majorana bound states: A story of clear advantage over conventional detection scheme VIVEKANANDA ADAK, Aabir Mukhopadhyay, Suman J De, Udit Khanna, Sumathi Rao, Sourin Das A hybrid setup consisting of a superconductivity-proximitized quantum spin Hall (QSH) insulator and a quantum anomalous Hall (QAH) insulator is proposed for chiral injection of electrons into the Majorana bound state (MBS). An unexplored region of the phase space involving the Zeeman-field induced boost of the helical edge state is then proposed for the detection of the MBS. 2-D transport simulations of our proposed setup are compared with the corresponding setup in the absence of the QAH region, when moderate potential and magnetic disorder are included. The remarkable contrast between the two results demonstrates the possibility for an unprecedented immunity from disorder-induced masking of the MBS detection in our proposed setup. |
Wednesday, March 22, 2023 2:18PM - 2:30PM |
AAA09.00008: Thermal Signature of Majorana Fermion in a Josephson Junction Aabir Mukhopadhyay, Sourin Das Experimental attempts for the detection of Majorana bound state(MBS) are primarily based on two theoretical predictions: (1) 2e2/h resonant conductance peak at zero bias and (2) the 4π Josephson Effect, both of which rely heavily on the subgap physics of topological superconductors. In a complementary approach, we look for non-trivial signatures of MBS in heat transport across a Josephson Junction (JJ). Specifically, we consider a thermally biased JJ hosting a pair of MBS in a helical edge state of a2D topological insulator. We show that the presence of Majorana endstates in a three-terminal JJ setup results in two sets of testable relations(1): |
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