# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1903.07787