Axion electrodynamics in curved emergent spacetime

ORAL

Abstract

The magnetoelectric response in condensed matter physics has recently been mapped to a hypothetical elementary particle, the axion. The existence of the axion was postulated in 1977 to resolve the strong charge-parity problem in quantum chromodynamics (QCD). While the QCD axion remains elusive, some topological materials are able to host exact analogues to the axion field. The axion response in condensed matter falls into two categories: (i) the background axion field which can become quantized in the presence of pseudoscalar-symmetry, giving 3D topological insulators their characteristic θ=π, and (ii) the dynamical axion where spontaneous symmetry breaking promotes the axion angle to a dynamical field, mimicking the QCD axion.

One instance of the dynamical axion field manifests as the phase of the charge density wave in Weyl semimetals. Deformations of the Weyl cones can lead to concepts of emergent spacetimes, which can be modulated by strain, inhomogeneities, and external drives. Such time-reversal-symmetry breaking fields or inversion-symmetry breaking fields allow the condensed matter system to take on a variety of spacetime environments beyond Minkowski flat space, e.g. a black hole event horizon. In this way, we can create in a crystal a unique sandbox to explore the effects of spatial curvature on topological and axion responses.

* This work is supported by the Quantum Science Center (QSC), a National Quantum Information Science Research Center of the U.S. Department of Energy (DOE).

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Presenters

  • Emily M Been

    University of California, Los Angeles

Authors

  • Emily M Been

    University of California, Los Angeles

  • Olivia Liebman

    College of Letters and Science, University of California, Los Angeles (UCLA), University of California, Los Angeles

  • Jonathan B Curtis

    UCLA, University of California, Los Angeles

  • Ioannis Petrides

    UCLA, College of Letters and Science, University of California, Los Angeles (UCLA), University of California, Los Angeles

  • Prineha Narang

    College of Letters and Science, University of California, Los Angeles (UCLA), CA, USA., University of California Los Angeles, College of Letters and Science, University of California, Los Angeles (UCLA), UCLA, University of California, Los Angeles, College of Letters and Science, University of California, Los Angeles, Harvard University