Theory of Non-Reciprocal Optical Effects in Antiferromagnets: The Case Cr_2O_3

TL;DR

This paper develops a microscopic model explaining non-reciprocal optical effects in antiferromagnetic Cr_2O_3, highlighting the role of spin-orbit coupling and symmetry breaking in these phenomena.

Contribution

It introduces a detailed microscopic framework linking light interactions to antiferromagnetic order via spin-orbit effects and symmetry considerations.

Findings

Calculated matrix elements for second harmonic generation.

Analyzed gyrotropic birefringence in Cr_2O_3.

Identified key symmetry-breaking mechanisms.

Abstract

A microscopic model of non-reciprocal optical effects in antiferromagnets is developed by considering the case of Cr_2O_3 where such effects have been observed. These effects are due to a direct coupling between light and the antiferromagnetic order parameter. This coupling is mediated by the spin-orbit interaction and involves an interplay between the breaking of inversion symmetry due to the antiferromagnetic order parameter and the trigonal field contribution to the ligand field at the magnetic ion. We evaluate the matrix elements relevant for the non-reciprocal second harmonic generation and gyrotropic birefringence.