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

• Published in: Nature communications Vol. 10; no. 1; pp. 2371 - 8
• Main Authors: Wu, Meng, Li, Zhenglu, Cao, Ting, Louie, Steven G.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 30.05.2019; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/1019; 639/301/1034; 639/766/119; 639/766/119/997; Bethe-Salpeter equation; Circular dichroism; Crystal structure; Crystals; Dependence; Dichroism; Energy; Ferromagnetism; First principles; Humanities and Social Sciences; Insulators; Iodine; Ligands; Magnetic properties; Magnetism; Magnets; MATERIALS SCIENCE; multidisciplinary; Optoelectronic devices; Science; Science (multidisciplinary); Substrates; Thin films
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-10325-7

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. The magneto-optical (MO) effects probe the electronic and magnetic properties of a material, particularly useful for 2D magnets. Here, the authors show that the large optical and MO responses in ferromagnetic monolayer CrI 3 arise from strongly bound excitons, extending over several atoms.