First-principles calculations of tunable magnetic and excitonic effects in a 2D magnetic semiconductor

In two-dimensional (2D) van der Waals (vdW) magnetic semiconductors, magnetic coupling between neighboring layers adds an entirely new degree of freedom to the tunable interlayer coupling, making their optical properties tunable by changing the underlying magnetism. As a 2D vdW magnetic semiconductor, layered CrSBr is ferromagnetic within each layer, and antiferromagnetically coupled between neighboring layers. In this talk, using first-principles density functional theory (DFT) and GW Bethe-Salpeter equation (GW-BSE) calculations, we demonstrate that the 2D magneto-excitons in this material hold distinct features from those in CrI₃. By tuning the external magnetic field and using other control knobs, the magnetic order in layered CrSBr is switchable, which results in drastically modified excitonic transitions revealed by GW-BSE calculations. We further connect our theory and calculations to experimental observations.