Theory of anomalous optical properties of bulk Rashba conductor

TL;DR

This paper theoretically investigates the optical properties of bulk Rashba conductors, revealing their potential as hyperbolic metamaterials and predicting enhanced directional dichroism due to magnetization effects.

Contribution

It introduces a theoretical framework for understanding the optical responses of Rashba conductors, highlighting their hyperbolic behavior and magnetization-induced anisotropic propagation.

Findings

Softening of plasma frequency for electric fields perpendicular to Rashba field

Prediction of hyperbolic electromagnetic metamaterial behavior

Enhanced directional dichroism with magnetization due to interband transitions

Abstract

The Rashba interaction induced when inversion symmetry is broken in solids is a key interaction connecting spin and charge for realizing novel magnetoelectric cross-correlation effects. Here, we theoretically explore the optical properties of a bulk Rashba conductor by calculating the transport coefficients at finite frequencies. It is demonstrated that the combination of direct and inverse Edelstein effects leads to a softening of the plasma frequency for the electric field perpendicular to the Rashba field, resulting in a hyperbolic electromagnetic metamaterial. In the presence of magnetization, a significant enhancement of anisotropic propagation (directional dichroism) is predicted because of interband transition edge singularity.Based on an effective Hamiltonian analysis, the dichroism is demonstrated to be driven by toroidal and quadratic moments of the magnetic Rashba system. The effective theory of the cross-correlation effects has the same mathematical structure as that of insulating multiferroics.