Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B67: Unconventional Transport Phenomena in Three-Dimensional Dirac and Weyl SemimetalsInvited
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Sponsoring Units: DCMP Chair: Alexander Balatsky, Los Alamos National Laboratory Room: Four Seasons 2-3 |
Monday, March 2, 2020 11:15AM - 11:51AM |
B67.00001: Fractional Quantum Hall Effect in Weyl Semimetals Invited Speaker: Anton Burkov Weyl semimetal may be thought of as a gapless topological phase protected by the chiral anomaly, where the symmetries involved in the anomaly are the U(1) charge conservation and the crystal translational symmetry. The absence of a band gap in a weakly-interacting Weyl semimetal is mandated by the electronic structure topology and is guaranteed as long as the symmetries and the anomaly are intact. |
Monday, March 2, 2020 11:51AM - 12:27PM |
B67.00002: Nonlinear dynamic conductivity in structrurally chiral Weyl semimetals Invited Speaker: Joseph Orenstein WSMs are 3D versions of graphene, characterized by isolated band crossings which act as monopoles of the Berry curvature field. From the properties of the Berry curvature under time-reversal and inversion, it follows that breaking either T or I is necessary for a crystal to exhibit a WSM phase. I-breaking WSMs exhibit response functions that are forbidden in systems that possess a center of symmetry. We have investigated an important example of such responses: the second-order nonlinear conductivity, defined by Ji = σijk.EiEj. For monochromatic electric fields the nonlinear response generates dc currents whose direction is dependent on the polarization state of the electric field, giving rise to phenomena known as photogalvanic effects (PGEs). In this talk I will present results on PGEs in response to linear and circular polarized light (LPGE and CPGE, respectively) as probes of both the symmetry and topology of the WSM phase. RhSi is an ideal candidate for such a study, as point group symmetry predicts the simplest possible structure of σijk , in which the only nonvanishing tensor elements are even and odd permutations of xyz. Furthermore, RhSi is structurally chiral (or handed), and the absence of mirror planes breaks the degeneracy of Weyl nodes of opposite Berry monopole charge. I will present results on the polarization selection rules and spectra of PGEs for light incident on 111 and 001 surfaces. On 111 we observe a CPGE current whose direction is parallel to the wavevector of the light and whose spectrum is consistent with photoexcitation across a Weyl cone. More surprising is that we observe in-plane CPGE and LPGE currents at normal incidence on the 001 surface, where the bulk point group predicts a null effect. I discuss the possibility that the current is allowed because truncation at the 001 surface breaks the nonsymmorphic (screw) symmetry and therefore may derive from helicoidal surface bands that give rise to Fermi arcs (see Chang et al. 1906.03207). |
Monday, March 2, 2020 12:27PM - 1:03PM |
B67.00003: Universal plateau in the thermoelectric Hall conductivity of Dirac/Weyl semimetals Invited Speaker: Brian Skinner The three-dimensional Dirac and Weyl semimetals can exhibit thermoelectric properties that are not possible in conventional metals and semiconductors. Here I focus in particular on the thermoelectric Hall effect, which is the generation of a transverse heat current upon applying an electric field in the presence of a magnetic field. I show, in particular, that the thermoelectric Hall conductivity acquires a robust plateau in the extreme quantum limit, and that the plateau value is independent of the field strength, disorder strength, carrier concentration, or carrier sign. I then discuss recent experiments on the three-dimensional Dirac semimetal ZrTe5, which clearly exhibit this plateau. Other thermoelectric coefficients in the material, such as the thermopower and Nernst coefficient, are greatly enhanced over their zero-field values even at relatively low fields. |
Monday, March 2, 2020 1:03PM - 1:39PM |
B67.00004: Pseudo-electromagnetic fields in topological semimetals Invited Speaker: Roni Ilan Dirac and Weyl semimetals react to position- and time-dependent perturbations, such as strain or an inhomogeneous magnetisation, as if emergent electromagnetic fields were applied. Such pseudo-electromagnetic fields differ from external electromagnetic fields in their symmetries and phenomenology, and enable a simple and unified description of a variety of inhomogeneous systems. We review the different mechanisms for creating effective pseudo-fields and their observable consequences, which can be remarkably different from those resulting from external fields. |
Monday, March 2, 2020 1:39PM - 2:15PM |
B67.00005: Acoustics, Weyl, and chiral transport Invited Speaker: Sebastian Huber Weyl semimetals in an external field exhibit a number of interesting transport phenomena. Here we show how we can induce pseudo-magnetic and electric fields in acoustics, how they modify the transport of acoustic energy and what we can learn from these systems for electronic transport in Weyl semimetals. Moreover, we demonstrate on a concrete model how one can capitalize on Weyl physics to create platform 9 3/4 at King's Cross station. |
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