Effective Hamiltonian theory for nonreciprocal light propagation in magnetic Rashba conductor

TL;DR

This paper develops an effective Hamiltonian for magnetic Rashba conductors, revealing how toroidal and quadrupole moments influence nonreciprocal light propagation and magneto-optical effects.

Contribution

It introduces a novel effective Hamiltonian framework for magnetic Rashba conductors, linking electromagnetic effects to toroidal and quadrupole moments.

Findings

Toroidal moment causes anisotropic light propagation.

Quadrupole moment leads to Faraday rotation.

Intrinsic spin current induces Doppler shift.

Abstract

Rashba spin-orbit interaction leads to a number of electromagnetic cross-correlation effects by inducing a mixing of electric and magnetic degrees of freedom. In this study, we investigate the optical properties of a magnetic Rashba conductor by deriving an effective Hamiltonian based on an imaginary-time path-integral formalism. We show that the effective Hamiltonian can be described in terms of toroidal and quadrupole moments, as has been argued in the case of insulator multiferroics. The toroidal moment turns out to coincide with the spin gauge field induced by the Rashba field. It causes Doppler shift by inducing intrinsic spin current, resulting in anisotropic light propagation (directional dichroism) irrespective of the polarization. The quadrupole moment on the other hand results in a magneto-optical phenomenon such as a Faraday effect for circularly-polarized waves.