Magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulators

TL;DR

This paper explores how magneto-optical Kerr and Faraday effects can be used to detect and manipulate bilayer antiferromagnetic insulators, revealing distinct optical signatures for topological versus trivial phases.

Contribution

It demonstrates that breaking mirror symmetries induces measurable Kerr and Faraday effects in bilayer antiferromagnetic insulators, enabling optical detection of topological states.

Findings

Kerr and Faraday effects occur when mirror symmetries are broken.

AFMTI shows sharp peaks at interband transition thresholds.

Large Kerr and Faraday angles enable pure magneto-optical rotation.

Abstract

Control and detection of antiferromagnetic topological materials are challenging since the total magnetization vanishes. Here we investigate the magneto-optical Kerr and Faraday effects in bilayer antiferromagnetic insulator MnBi$_2$Te$_4$. We find that by breaking the combined mirror symmetries with either perpendicular electric field or external magnetic moment, Kerr and Faraday effects occur. Under perpendicular electric field, antiferromagnetic topological insulators (AFMTI) show sharp peaks at the interband transition threshold, whereas trivial insulators show small adjacent positive and negative peaks. Gate voltage and Fermi energy can be tuned to reveal the differences between AFMTI and trivial insulators. We find that AFMTI with large antiferromagnetic order can be proposed as a pure magneto-optical rotator due to sizable Kerr (Faraday) angles and vanishing ellipticity. Under external magnetic moment, AFMTI and trivial insulators are significantly different in the magnitude of Kerr and Faraday angles and ellipticity. For the qualitative behaviors, AFMTI shows distinct features of Kerr and Faraday angles when the spin configurations of the system change. These phenomena provide new possibilities to optically detect and manipulate the layered topological antiferromagnets.