Transmission/reflection coefficients and Faraday/Kerr rotations as a function of applied magnetic fields in spin-orbit coupled Dirac metals

TL;DR

This paper studies how light propagates and reflects in Weyl metals with broken time reversal symmetry, revealing unique magnetically controlled optical effects predicted by axion electrodynamics.

Contribution

It demonstrates the magnetic-field dependence of transmission, reflection, and Faraday/Kerr rotations in Weyl metals, highlighting their role as chiral prisms and signatures of axion electrodynamics.

Findings

Light splits into three waves depending on chirality and polarization.

External magnetic fields control Faraday/Kerr rotation directions.

Linear polarization along propagation occurs when Weyl nodes align with magnetic field.

Abstract

We reveal the nature of propagation and reflection of light in Weyl metals with broken time reversal symmetry, whose electromagnetic properties are described by axion electrodynamics. These Weyl metals turn out to play the role of a chiral prism: An incident monochromatic wave can split into three waves propagating with different wave numbers, depending on its chirality and polarization (right $\&$ left circular polarizations and linear polarization along the propagating direction). The helicity of the propagating/reflected light is determined by $\textbf{B}_{ext}$ and $\textbf{E}_{light}$, where $\textbf{B}_{ext}$ is the gradient of the $\theta-$field in the axion term given by the applied magnetic field and $\textbf{E}_{light}$ is the electric-field component of the incident light. This implies that the direction of the external magnetic field controls the Faraday/Kerr rotation. In particular, we find that the linear polarization of the oscillating electric field along the propagating direction, which cannot occur in conventional metals, arises when Weyl nodes are aligned along the oscillating magnetic field. We evaluate both transmission/reflection coefficients and Faraday/Kerr rotation angles as a function of both an external magnetic field and frequency for various configurations of light propagation. We propose their strong magnetic-field dependencies as one of the fingerprints of the axion electrodynamics.