Frequency-dependent Faraday and Kerr rotation in anisotropic nonsymmorphic Dirac semimetals

TL;DR

This paper investigates the frequency-dependent magneto-optic effects in anisotropic nonsymmorphic Dirac semimetals, revealing finite zero-frequency Faraday rotation and a logarithmic enhancement near the absorption edge, with implications for magneto-optic devices.

Contribution

It provides a theoretical analysis of Faraday and Kerr rotations in anisotropic Dirac semimetals under Zeeman coupling, highlighting their potential for magneto-optic applications.

Findings

Finite zero-frequency Faraday rotation angle of 2α_F

Logarithmic enhancement of rotation angles near absorption edge

Impurity scattering reduces but does not eliminate the enhancement

Abstract

We calculate the frequency-dependent longitudinal and Hall conductivities and the Faraday and Kerr rotation angles for a single sheet of anisotropic Dirac semimetal protected by nonsymmorphic symmetry in the presence of a Zeeman term coupling to the out-of-plane component of the spin. While the Zeeman term causes a rotation of the plane of polarization of the light, the anisotropy causes the appearance of an elliptically polarized component in an initially linearly polarized beam. The two effects can be combined in a single complex Faraday rotation angle. At the zero-frequency limit, we find a finite value of the Faraday rotation angle, which is given by $2\alpha_F$, where $\alpha_F$ is the effective fine structure constant associated with the velocity of the linearly dispersing Dirac fermions. We also find a logarithmic enhancement of the Faraday (and Kerr) rotation angles as the frequency of the light approaches the absorption edge associated with the Zeeman-induced gap. While the enhancement is reduced by impurity scattering, it remains significant for an attainable level of material purity. These results indicate that two-dimensional Dirac materials protected by nonsymmorphic symmetry are responsive to Zeeman couplings and can be used as platforms for magneto-optic applications, such as the realization of polarization-rotating devices.