Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H01: Fermi Surface and Excitations of Weyl SystemsFocus

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Sponsoring Units: DCMP Chair: Ryo Okugawa, Tohoku University Room: BCEC 106 
Tuesday, March 5, 2019 2:30PM  2:42PM 
H01.00001: SemiQuantized Pumping and SpinOrbit Torque in Topological Dirac Semimetals Takahiro Misawa, Kentaro Nomura We study the spin/charge transport phenomena and magnetization switching in a topological Dirac semimetal attached to a ferromagnetic insulator. Topological Dirac semimetals manifest a large inverse spin Hall effect when a spin current is pumped from the attached ferromagnetic insulator with a precessing magnetization, compared to conventional normal metals. We show that the induced charge current is semiquantized because it originates to topological nature. We also show that an applied electric field in the topological Dirac semimetal generates the spinorbit torque which reverses the magnetization in the ferromagnet. 
Tuesday, March 5, 2019 2:42PM  2:54PM 
H01.00002: Disordered fermionic quantum critical points Hennadii Yerzhakov, Joseph Maciejko <!StartFragment>We study the effect of shortrange quenched disorder on the semimetalsuperconductor quantum phase transition in a model of twodimensional Dirac semimetal with N flavors of twocomponent Dirac fermions, using perturbative renormalization group methods at oneloop order in 4ε spatial and ε_{τ} time dimensions. Depending on the value of N, the model is applicable to topological insulators (odd N), graphene (N=4), and possibly other systems and type of transitions. For N≥2 we find that the Harrisstable clean critical behavior gives way, past a certain critical disorder strength, to a finitedisorder critical point characterized by nonGaussian critical exponents, a noninteger dynamic critical exponent, and a finite Yukawa coupling between Dirac fermions and bosonic order parameter fluctuations. For sufficiently large N the disordered quantum critical point is described by a renormalization group fixed point of stablefocus type and exhibits oscillatory corrections to scaling.<!EndFragment> 
Tuesday, March 5, 2019 2:54PM  3:06PM 
H01.00003: Chirality Josephson current in inversionasymmetric Weyl semimetals Songbo Zhang, Johanna Erdmenger, Bj\"orn Trauzettel In this report, I will talk about Josephson junctions based on inversionasymmetric but timereversal symmetric Weyl semimetals under the influence of Zeeman fields. Due to distinct spin textures, the Weyl nodes of opposite chirality respond differently to an external magnetic field. Remarkably, a Zeeman field perpendicular to the junction direction results in a phase shift of opposite sign in the currentphase relations of opposite chirality. This leads to a finite chirality Josephson current even in the absence of a phase difference across the junction. In the long junction and zero temperature limit, the chirality Josephson current embodies a novel quantum anomaly at $\pi$ phase difference which is associated with a $\mathbb{Z}_2$ symmetry at low energies. It can be detected experimentally via an anomalous Fraunhofer pattern. 
Tuesday, March 5, 2019 3:06PM  3:18PM 
H01.00004: Generalized TripleComponent Fermions: Lattice Model, Fermi arcs and Anomalous Transport Snehasish Nandy, Sourav Manna, Dumitru Calugaru, Bitan Roy A generalization of timereversal symmetrybreaking triplecomponent semimetals, transforming under the pseudospin1 representation, to arbitrary (anti)monopole charge $2 n$, with $n=1,2,3$ in the crystalline environment will be presented. The quasiparticle spectra of such systems are composed of two dispersing bands with pseudospin projections $m_s=\pm 1$ and one completely flat band at zero energy with $m_s=0$. In this talk we will show simple tightbinding models for such spin1 excitations in a cubic lattice and address the symmetry protection of the generalized triplecomponent nodes. In accordance to the bulkboundary correspondence, triplecomponent semimetals support $2 n$ branches of topologically protected Fermi arc surface states and accommodate a large anomalous Hall conductivity (in the $xy$ plane), given by $\sigma^{\rm 3D}_{xy} \propto 2 n \times$ the separation of the triplecomponent nodes (in units of $e^2/h$). Furthermore, we compute the longitudinal magneto, planar Hall and magneto thermalconductivities in this system, which increase as $B^2$ (due to the nontrivial Berry curvature in the medium) with the external magnetic field ($B$), when it is sufficiently weak. A generalization of our construction to arbitrary integer spin system is also highlighted. 
Tuesday, March 5, 2019 3:18PM  3:30PM 
H01.00005: Magnetic field induced valley polarization in a Weyl semimetal with tilted cones. Simon Bertrand, Rene Cote, Ion Garate We present a theory of the optical conductivity in timereversal symmetric Weyl semimetals with tilted cones placed under strong magnetic fields. Our theory incorporates long range Coulomb interactions treated within the generalized random phase approximation. 
Tuesday, March 5, 2019 3:30PM  3:42PM 
H01.00006: Thermoelectric transport in torsional strained Weyl semimetals Enrique Munoz, Rodrigo Soto Garrido We recently^{1} studied the electronic transport properties in Weyl semimetals submitted to the combined eects of torsional mechanical strain and magnetic field, showing that this conguration induces a nodepolarization eect on the current that can be used to measure the torsion angle from transmission experiments. In this talk, we extend our previous work to study thermoelectric transport in Weyl 
Tuesday, March 5, 2019 3:42PM  3:54PM 
H01.00007: "FirstPrinciples Studies of Topological Semimetal Features in the Nonpolar Phase of Ferromagnetic Hexgonal Manganites YXO_{3} (X=VCo)" Sophie Weber, Sinead Magella Griffin, Jeffrey B Neaton Hexagonal Manganites have garnered much attention in the condensed matter community due to their multiferroic properties. Here, we use first principles calculations to examine the topological properties of their band structures. While the noncollinear antiferromagnetism common in this compound class generally yields insulating states, we find that energeticallynearby ferromagnetic ordering can cause metallic band structures with topological nodal features in the nonpolar P6_{3}/mmc phase. Starting with YMnO_{3} we substitute different 3d transition metals for Mn and examine the resultant trends in band structure as a function of B site cation. In particular we find that YVO_{3} and YCrO_{3} have nodal lines near the Fermi level due a band inversion which can be tuned via biaxial strain. Based on our findings, stabilizing YXO_{3} compounds in the hexagonal ferromagnetic phase, for example via epitaxial growth, can offer a promising platform for studying the interplay of topology and multiferroicity. 
Tuesday, March 5, 2019 3:54PM  4:06PM 
H01.00008: Topological nodal phases in nonHermitian systems with paritytime and parityparticlehole symmetries Ryo Okugawa, Takehito Yokoyama Exceptional points emerge from band touching in nonHermitian systems. We study band degeneracy in nonHermitian systems with paritytime and parityparticlehole symmetries. When paritytime or parityparticlehole symmetry is present, it is shown that exceptional lines and surfaces can appear in twodimensional and threedimensional nonHermitian systems, respectively. We also investigate topological properties of the nodal band structures. We demonstrate the nonHermitian topological nodal phases by using lattice models of a topological semimetal and a superconductor. 
Tuesday, March 5, 2019 4:06PM  4:18PM 
H01.00009: Berry curvature and Hall viscosities in an anisotropic Dirac semimetal Francisco PenaBenitez, Kush Saha, Piotr Surowka We investigate parityodd nondissipative transport in an anisotropic Dirac semimetal in two spatial dimensions. The analysis is relevant for interacting electronic systems with merging Dirac points at charge neutrality. For such systems the dispersion relation is relativistic in one direction and nonrelativistic in the other. We give a proposal how to calculate the Berry curvature for this system and use it to derive more than one odd viscosities, in contrast to rotationally invariant systems. We observe that in such a model the odd part of stress tensor is parameterised by two independent transport coefficients and one that is identically zero. 
Tuesday, March 5, 2019 4:18PM  4:30PM 
H01.00010: Duality between dielectricity and diamagnetism in Dirac materials in analogy with quantum electrodynamics Hideaki Maebashi, Masao Ogata, Hidetoshi Fukuyama We theoretically investigate the electrodynamics of narrowgap electron systems in the presence of strong spinorbit interaction treated as threedimensional Dirac materials. In parallel to quantum electrodynamics (QED), we derive analytic expressions of the wavenumber and frequencydependent electric and magnetic susceptibilities of the narrowgap systems at zero temperature. When the chemical potential is inside the band gap, the ratio of the electric to magnetic susceptibilities is shown to be a negative constant for arbitrary wave number and frequency in analogy with vacuum polarization in QED [H. Maebashi, M. Ogata, and H. Fukuyama, J. Phys. Soc. Jpn. 86, 083702 (2017)]. On the other hand, when the chemical potential lies in the conduction or valence band, we obtain the plasmon dispersion where the background permittivity is microscopically determined, which is significantly enhanced along with large diamagnetism known as a result of interband effect of magnetic field. Such a duality between dielectricity and diamagnetism can be traced to effective Lorentz covariance which Dirac materials have. 
Tuesday, March 5, 2019 4:30PM  4:42PM 
H01.00011: Magnetotransport in multiWeyl semimetals: A kinetic theory approach Renato Dantas, Francisco PenaBenitez, Piotr Surowka, Bitan Roy Longitudinal magnetotransport in threedimensional multiWeyl semimetals, constituted by a pair of (anti)monopole of arbitrary integer charge (n), with n=1,2 and 3 in a crystalline environment, will be presented. We will show that for any n>1, even though the distribution of the underlying Berry curvature is anisotropic, the corresponding intrinsic component of the longitudinal magnetoconductivity (LMC), bearing the signature of the chiral anomaly, is insensitive to the direction of the external magnetic field (B) and increases as $B^2$, at least when it is sufficiently weak (the semiclassical regime). In addition, the LMC scales as $n^3$ with the monopole charge. We demonstrate these outcomes for two distinct scenarios, namely when interparticle collisions in the Weyl medium are effectively described by (a) a single and (b) two (corresponding to intervalley and intravalley) scattering times. While in the former situation the contribution to LMC from chiral anomaly is inseparable from the nonanomalous ones, these two contributions are characterized by different time scales in the later construction. Specifically for sufficiently large intervalley scattering time the LMC is dominated by the anomalous contribution, arising from the chiral anomaly. 
Tuesday, March 5, 2019 4:42PM  4:54PM 
H01.00012: Geometric signatures of topological origin in the particlehole continuum of Weyl semimetals ANIRUDH CHANDRASEKARAN, Stefanos Kourtis We present a full geometric description of the particlehole continuum in Weyl semimetals, emphasizing distinctive features in the joint density of states for particlehole excitations across nodal points. These are shown to arise as a geometric consequence of the linear effective Hamiltonian around nodal points, and are thus characteristic of Weyl semimetals. We discuss how such geometric characteristics of the particlehole continuum of Weyl semimetals can be present in resonant inelastic Xray scattering (RIXS) spectra. Our work provides signatures of the presence of Weyl nodes in bulk band structures, and indicates that RIXS is a promising tool that can potentially be used to identify and characterize nodal points in materials, especially in settings that are difficult to access with other spectroscopies. The calculation presented here also serves as a first checkpoint for comparison with ongoing RIXS experiments. 
Tuesday, March 5, 2019 4:54PM  5:06PM 
H01.00013: Nonabelian braiding of Weyl points Adrien Bouhon, RobertJan Slager, Tomas Bzdusek We discuss the realization of nonabelian braiding of Weyl points in a twodimensional crystal. This proposal is based on a refined homotopy characterization of band structures that goes beyond the current classification of crystalline topological phases of matter. 
Tuesday, March 5, 2019 5:06PM  5:18PM 
H01.00014: The disordered single Weyl cone Jed Pixley, Justin Wilson, David Huse, Sankar Das Sarma We numerically study a single Weyl cone in the presence of shortrange disorder. By representing the Hamiltonian in a ``mixed’’ way between real and momentum space we are able to invoke fast Fourier transforms to take advantage of efficient numerical routines (such as Lanczos and the kernel polynomial method) that rely on sparse matrixvector multiplications. As a result, we can reach sufficiently large system sizes that are comparable to lattice model simulations. We study the distinctions that arise between lattice models that contain band curvature and multiple Weyl nodes that have internode scattering with the case of a single Weyl node with a perfectly linear dispersion. We will report results on the nature of rare regions and the density of states as a function of the strength of disorder as well as compare and contrast single node and multinode situations. 
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