Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session Y01: Interactions and Dynamics in Topological SemimetalsFocus

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Sponsoring Units: DCMP Room: BCEC 106 
Friday, March 8, 2019 11:15AM  11:27AM 
Y01.00001: Quantum oscillations in Dirac/Weyl semimetals due to strain and external fields Dmitry Pikulin, Roni Ilan I will discuss how strain can cause quantum oscillations in Dirac/Weyl semimetals. In particular, I will concentrate on quasiclassical trajectories formed by strain alone and how they are modified in presence of external field. I will mention both bulk and bulkboundary quantum oscillations. 
Friday, March 8, 2019 11:27AM  11:39AM 
Y01.00002: Theory of spin torque in Weyl semimetals with magnetic texture Daichi Kurebayashi, Kentaro Nomura We theoretically study the spintransfer torque, a fundamental physical quantity to understand the electricallyinduced dynamics of magnetic texture. We calculate the electricallyinduced nonequilibrium spin density of a Weyl semimetal (WSM) and obtain the analytical expression of the spin torque corresponding to a nonadiabatic spintransfer torque. Importantly, the strength of the obtained spin torque outstrips that of conventional ferromagnetic metals when magnetization varies steeply. Furthermore, due to the suppression of longitudinal conductivity in this regime, the dissipation due to Joule heating for the spintransfer torque is smaller than that in conventional ferromagnetic metals. We also analyze the dynamics of the domain walls driven using the spintransfer torque and find that the velocity of the domain wall is one order of magnitude greater than that of a conventional ferromagnetic nanowire. Consequently, the fastcontrol of domain walls can be achieved with smaller dissipation in the WSM. Therefore, the WSM can be a new candidate for application to spintronics devices such as the racetrack memory. 
Friday, March 8, 2019 11:39AM  11:51AM 
Y01.00003: Counting formula for the pseudo Landau levels visible in an energy spectrum Toshikaze Kariyado One interesting feature of Dirac/Weyl systems is that spatial modulation, for instance given by strain, can be regarded as a gauge filed. This “pseudo” gauge field can generate pseudo magnetic field, and enables us to observe magnetic like phenomena such as Landau level formation or quantum oscillations even without external magnetic field. Here, by considering a simplest situation to have finite pseudo magnetic field, we derive a concise formula to count the number of pseudo Landau levels clearly visible in the energy spectrum. The derived formula is numerically verified in a toy model. Equipped with the formula, we also discuss the possible realization of the pseudo Landau levels in existing Dirac materials, particularly in antiperovskite Sr_{3}SnO series. 
Friday, March 8, 2019 11:51AM  12:03PM 
Y01.00004: Topological semimetal coupled to nanomechanical resonator Kun Woo Kim, Junho Suh The detection of gapless Dirac point in semimetals is an important issue for the characterization of topological phase. While the direct measurements of spectral functions and magnetoconductance are widely employed, the strength of electronic signal is vanishingly small near Dirac point due to its low density of states. Here, we propose a way to detect the presence of Dirac node through the coupling to a nano mechanical resonator. Playing as a nonlinear circuit element, the quantum capacitance of topological semimetal induces an abnormal frequency shifting in the resonator near Dirac node. This quantum and mechanical setup will be ideal for the characterization of various topological matter and its boundary states. 
Friday, March 8, 2019 12:03PM  12:15PM 
Y01.00005: Dirac cones protected by chiral symmetry in wallpaper groups ChingKai Chiu, Yang Zhesen, Congcong Le Dirac cones in 2D Brillioun zone (BZ) can be protected by chiral symmetry. The spinless and spin1/2 systems preserving chiral symmetry can be realized in timereversal symmetric superconductors and correspond to symmetry class BDI and DIII respectively. Since the total winding number in the entire BZ is zero, there are at least two Diracs cones in the BZ. Furthermore, crystalline symmetries lead to duplicate Dirac cones and additional constraints. The minimal numbers of the Dirac cones in the BZ under different symmetries might be different. In this talk, we classify the minimal numbers of the Dirac cones protected by chiral symmetry in all 17 wallpaper groups for class AIII, BDI, and DIII. 
Friday, March 8, 2019 12:15PM  12:27PM 
Y01.00006: Stability of the Semimetallic Phase in strongly interacting Weyl semimetals Johan Carlstrom, Emil J Bergholtz Using a combination of analytical arguments and diagrammatic Monte Carlo simulations, we show that the corrections to the dispersion in interacting Weyl semimetals are determined by the ultraviolet cutoff and the inverse screening length. If both of these are finite, then the diagrammatic series is convergent even in the lowtemperature limit, which implies that the semimetallic phase is protected by a symmetry of the self energy. We also find that the frequency dependent part of the self energy gives an extremely small correction to the Greens function of the interacting system, implying that the impact of interactions almost entirely takes the form of a renormalisation of the single particle dispersion. 
Friday, March 8, 2019 12:27PM  12:39PM 
Y01.00007: Straininduced nonlinear spin Hall effect in topological Dirac semimetal Yasufumi Araki Topological Dirac seimetals (TDSMs) form a new class of threedimensional topological semimetals, characterized by pair(s) of doublydegenerate nodal points (Dirac points) in their momentum(k)space band structures. They show the intrinsic spin Hall effect (SHE), which comes from the kspace topology around the Dirac points. This spin Hall conductivity is topologically protected, while it cannot be easily tuned or enhanced at linear response. 
Friday, March 8, 2019 12:39PM  12:51PM 
Y01.00008: Enhanced conductance of Weyl semimetals with straininduced chiral magnetic fields in the ultraquantum limit Jan Behrends, Jens Bardarson, Roni Ilan Magnetotransport is one of the key signatures of Weyl semimetals. It is believed to reveal the chiral anomaly, the nonconservation of chiral charge, by showing a large negative magnetoresistance for longitudinal transport. With the realization of chiral magnetic fields, fields that act with opposite sign on the two chiralities, transport experiments in presence of those fields come in sight. In this work, we show that the conductivity in the ultraquantum regime of a disordered Weyl semimetal subjected to a chiral magnetic field in transport direction increases with the field strength and width of the sample. We relate this increment to the spatial separation of counterpropagating modes in those samples. Our results are based on tightbinding simulations and supported by analytical arguments. We argue how this effect can be used in devices that need spatial separation of charge carriers. 
Friday, March 8, 2019 12:51PM  1:03PM 
Y01.00009: Ferromagnetic Weyl semimetal phase and anomalous Hall effect in stacked Kagome lattice Akihiro Ozawa, Kentaro Nomura Recently, Weyl semimetals, which have threedimensional linear dispersions near the Fermi energy have been intensively investigated. Especially, ferromagnetic Weyl semimetals are drawing attentions as a system which implements some novel transport phenomena such as the anomalous Hall effect. It is reported that ferromagnetic Weyl phase is realized in stacked Kagome material Co_{3}Sn_{2}S_{2} by experiment and first principle calculation. In this presentation, we study the electronic state and the transport properties including the anomalous Hall effect by constructing an effective tight binding Hamiltonian. We focus on d orbits of cobalt which form Kagome ABC stacked structure (Shandite) as an effective model and compute its electronic state. As a result, we detect ferromagnetic Weyl semimetal phase. Furthermore, in order to reveal the transport property, we compute the anomalous Hall conductivity by using the Kubo formula. The Hall conductivity becomes large when the Fermi energy resides around the Weyl points. 
Friday, March 8, 2019 1:03PM  1:15PM 
Y01.00010: ABSTRACT WITHDRAWN

Friday, March 8, 2019 1:15PM  1:27PM 
Y01.00011: "Hinge" surface states in Weyl semimetals Ryo Takahashi, Ryo Okugawa, Shuichi Murakami Topological insulators have anomalous surface states due to the bulkedge correspondence. In recent years, a higherorder topological insulator (HOTI) has been proposed. It is insulating both in the bulk and in the surface. However, it has anomalous gapless hinge states at the hinges, which are intersections of two surfaces. One interesting question here is whether we can define a gapless counterpart of the HOTI, i.e. a "higherorder" topological semimetal. As a step to answer this question, we study an intermediate Weyl semimetal phase between a normal insulator phase and an inversionsymmetric HOTI phase [1]. We investigate its hinge states and clarify how the hinge states develop from the Fermiarc surface states, which are wellknown anomalous surface states in Weyl semimetals. By using tightbinding models, we demonstrate that in some cases, gapless hinge states in topological semimetals are separated in the momentum space from gapless surface/bulk states. On the other hand, they may merge into gapless surface/bulk states in some cases. 
Friday, March 8, 2019 1:27PM  1:39PM 
Y01.00012: Nonlocal spinspin coupling in topological semimetals Sonu Verma, Debasmita Giri, Keshav Pareek, Herbert Fertig, Arijit Kundu We study the spinspin coupling in finitegeometry topological semimetals employing the RKKY theory of interaction among impurity spins. The impurity spins can be on the surface of the geometry, where the mediated interaction between them can be through the topological surface states. Alternatively, the impurity spins can be on opposite surface of the system, where the mediated interaction can be through the semimetalic bulk states, giving rise to signatures of possible nonlocal effects. 
Friday, March 8, 2019 1:39PM  1:51PM 
Y01.00013: Effects of longrange interactions on topological semimetals Shouvik Sur, Pallab Goswami In the presence of longrange interactions the low energy dynamics in a metal usually undergoes significant readjustments, leading to a state that qualitatively differs from that in the noninteracting limit. The band structures of many three dimensional systems host topologically protected nodalpoints or nodallines. In such semimetals longrange interactions play an important role in both the native phase, and upon tuning to a topological or geometric quantum critical point. Here we study the interplay of longrange interactions and topology in a nodalpoint semimetal. 
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