Physical origin of giant excitonic and magneto-optical responses in two-dimensional ferromagnetic insulators

TL;DR

This paper reveals that excitonic effects are the main cause of giant magneto-optical responses in 2D ferromagnetic insulators like CrI₃, providing insights for designing advanced optoelectronic devices.

Contribution

It demonstrates through first-principles calculations that excitonic effects dominate the optical and magneto-optical responses in 2D ferromagnetic insulators, clarifying their microscopic origin.

Findings

Excitonic effects dominate magneto-optical responses in CrI₃.

Predicted frequency- and substrate-dependent magneto-optical responses.

Provided physical understanding and design principles for 2D magnetic optoelectronics.

Abstract

The recent discovery of magnetism in atomically thin layers of van der Waals crystals has created great opportunities for exploring light-matter interactions and magneto-optical phenomena in the two-dimensional limit. Optical and magneto-optical experiments have provided insights into these topics, revealing strong magnetic circular dichroism and giant Kerr signals in atomically thin ferromagnetic insulators. However, the nature of the giant magneto-optical responses and their microscopic mechanism remain unclear. Here, by performing first-principles GW and Bethe-Salpeter equation calculations, we show that excitonic effects dominate the optical and magneto-optical responses in the prototypical two-dimensional ferromagnetic insulator, CrI$_3$. We simulate the Kerr and Faraday effects in realistic experimental setups, and based on which we predict the sensitive frequency- and substrate-dependence of magneto-optical responses. These findings provide physical understanding of the phenomena as well as potential design principles for engineering magneto-optical and optoelectronic devices using two-dimensional magnets.