Theory of Kerr and Faraday rotations and linear dichroism in Topological Weyl Semimetals.

Mehdi Kargarian,Nandini Trivedi,Mohit Randeria

doi:10.1038/srep12683

Abstract

We consider the electromagnetic response of a topological Weyl semimetal (TWS) with a pair of Weyl nodes in the bulk and corresponding Fermi arcs in the surface Brillouin zone. We compute the frequency-dependent complex conductivities σαβ(ω) and also take into account the modification of Maxwell equations by the topological θ-term to obtain the Kerr and Faraday rotations in a variety of geometries. For TWS films thinner than the wavelength, the Kerr and Faraday rotations, determined by the separation between Weyl nodes, are significantly larger than in topological insulators. In thicker films, the Kerr and Faraday angles can be enhanced by choice of film thickness and substrate refractive index. We show that, for radiation incident on a surface with Fermi arcs, there is no Kerr or Faraday rotation but the electric field develops a longitudinal component inside the TWS, and there is linear dichroism signal. Our results have implications for probing the TWS phase in various experimental systems.

Highlights

We consider the electromagnetic response of a topological Weyl semimetal (TWS) with a pair of Weyl nodes in the bulk and corresponding Fermi arcs in the surface Brillouin zone
A interesting state of matter is the topological Weyl semimetal (TWS)[5,6,8]. These are phases with broken time-reversal or inversion symmetry, whose electronic structure consists of pairs of Weyl nodes, points in the bulk Brillouin zone (BZ), which are at the chemical potential and act as sources and sinks of Berry curvature
We show that our predictions are sensitive to four nontrivial characteristics of a TWS: (i) the topological Weyl nodes which lead to nontrivial σxy in the absence of an applied field, (ii) the nodal excitations leading to optical conductivity σxx(ω) ~ ω, (iii) the unusual surface states with Fermi arcs, and (iv) the modification of Maxwell equations inside the TWS via a topological θ-term

Summary

Introduction

We consider the electromagnetic response of a topological Weyl semimetal (TWS) with a pair of Weyl nodes in the bulk and corresponding Fermi arcs in the surface Brillouin zone. A interesting state of matter is the topological Weyl semimetal (TWS)[5,6,8] These are phases with broken time-reversal or inversion symmetry, whose electronic structure consists of pairs of Weyl nodes, points in the bulk Brillouin zone (BZ), which are at the chemical potential and act as sources and sinks of Berry curvature. This is predicted[5] to lead to unusual surface states that are gapless on disconnected Fermi arcs with end points at the projections of the bulk nodes onto the surface BZ. We find Kerr and Faraday rotations www.nature.com/scientificreports/

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