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, CrI₃. 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.

最近在范德华晶体的原子薄层中发现了磁性，这为探索二维极限内的光-物质相互作用和磁光现象创造了巨大的机会。光学和磁光实验提供了对这些主题的见解，揭示了原子薄铁磁绝缘体中的强圆形磁二向色性和巨大的Kerr信号。但是，巨磁光响应的性质及其微观机制仍不清楚。在这里，通过执行第一性原理GW和Bethe-Salpeter方程计算，我们表明在典型的二维铁磁绝缘子CrI _3中，激子效应支配了光学和磁光响应。。我们在现实的实验设置中模拟了Kerr和Faraday效应，并据此预测了磁光响应的敏感频率和衬底依赖性。这些发现提供了对现象的物理理解以及使用二维磁体的工程磁光和光电设备的潜在设计原理。