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

TL;DR

This paper analyzes the electromagnetic response of topological Weyl semimetals, calculating Kerr and Faraday rotations influenced by Weyl node separation and film thickness, revealing enhanced effects and unique dichroism phenomena.

Contribution

It provides a detailed theoretical framework for Kerr and Faraday rotations in Weyl semimetals, including the effects of film thickness, substrate, and Fermi arcs, advancing understanding of their optical properties.

Findings

Kerr and Faraday rotations are larger in thin TWS films than in topological insulators.

Rotation angles can be enhanced by adjusting film thickness and substrate refractive index.

Fermi arcs cause no rotation but induce magnetic linear dichroism.

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 $\sigma_{\alpha\beta}(\omega)$ and also take into account the modification of Maxwell equations by the topological $\theta$-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 magnetic linear dichroism. Our results have implications for probing the TWS phase in various experimental systems.