Magneto-optical Kerr effect and signature of the chiral anomaly in a Weyl semimetal in a magnetic field

TL;DR

This paper investigates how the magneto-optical Kerr effect (MOKE) in tilted Weyl semimetals reveals signatures of the chiral anomaly, including valley polarization detection and plasmon frequency shifts under magnetic fields.

Contribution

It demonstrates how MOKE is altered in tilted Weyl semimetals and proposes using Kerr measurements to detect the chiral anomaly and valley polarization.

Findings

Large Kerr angle peak at plasmon frequency in Voigt configuration

Blueshift of the Kerr peak with increasing magnetic field as a chiral anomaly signature

MOKE can detect valley polarization in Weyl semimetals

Abstract

One striking property of the Landau level spectrum of a Weyl semimetal (WSM) is the existence of a chiral Landau level, in which the electrons propagate unidirectionally along the magnetic field. This linearly dispersive level influences the optical properties of WSMs. For example, it was recently shown that a complete optical valley polarization is achievable in a time-reversal symmetric Weyl semimetal placed in a magnetic field\cite% {Bertrand2019}. This effect originates from inter-Landau level transitions involving the chiral Landau level and requires a tilt of the Weyl cones. In this paper, we show how the magneto-optical Kerr effect (MOKE) is modified in a WSM\ with tilted Weyl cones in comparison with its behavior in a normal metal and how a valley polarization can be detected using MOKE. We study both the Faraday (longitudinal) and Voigt (transverse) configurations for light incident on a semi-infinite WSM surface with no Fermi arcs. We use a minimal model of a WSM with four tilted Weyl nodes related by mirror and time-reversal symmetry. In the Voigt configuration, a large peak of the Kerr angle occurs at the plasmon frequency. We show that the blueshift in frequency of this peak with increasing magnetic field is a signature of the chiral anomaly in the MOKE.