Giant Magneto-Optical Effects in Two-Dimensional Flat-Band Antiferromagnets

TL;DR

This paper demonstrates giant magneto-optical effects in 2D flat-band antiferromagnets, especially in monolayer RuOCl2, revealing potential for advanced 2D opto-spintronic devices through first-principles calculations.

Contribution

It uncovers unprecedented large magneto-optical responses in 2D flat-band antiferromagnets, highlighting the role of flat bands in enhancing nonlinear optical effects.

Findings

Record-large second-order magneto-optical Schafer-Hubert effect with 28° polarization rotation.

High anisotropic optical absorption and broadband hyperbolic windows across visible spectrum.

Giant linear dichroism reaching 50%, surpassing other 2D magnetic systems.

Abstract

In this work, we reveal giant magneto-optical responses in two-dimensional(2D) antiferromagnets with nearly flat electronic bands, based on first-principles calculations and group-theoretical analysis. We identify a record-large second-order magneto-optical Schafer-Hubert(SH) effect, featuring a polarization rotation angle of 28 degree, in monolayer antiferromagnetic RuOCl2, driven by flatband-enhanced interband optical transitions. Both the valence and conduction bands exhibit pronounced directional flatness, giving rise to highly anisotropic optical absorption and broadband hyperbolic frequency windows spanning the entire visible spectrum. This anisotropy leads to an exceptionally strong linear dichroism (LD) reaching 50%, far exceeding values reported in other 2D magnetic systems. Remarkably, the giant SH effect and LD appear at distinct photon energies, reflecting a momentum-direction-dependent crossover between flat and dispersive bands. Both responses are further amplified with increasing RuOCl2 film thickness. Our results establish flat-band antiferromagnets as a fertile platform for realizing giant nonlinear magneto-optical effects and open new avenues for 2D opto-spintronic device applications.