Twist-Dependent Interlayer Coupling, Excitons, and Anisotropy in a Two-Dimensional Semiconducting Magnet

Two dimensional (2D) van der Waals (vdW) semiconducting magnets are a new class of quantum materials for studying the emergent physics of excitons and spins in a 2D limit. Twists have been a powerful tool to manipulate the band structures and magnetisms of 2D vdW magnets and have led to unconventional magnetic ground states. However, how the interlayer coupling, excitons, and anisotropy, which determine the magnetic and optical properties of 2D magnets, change with the twist remain unclear. Here we report a comprehensive study on twist-dependent interlayer coupling, exciton energy, and dielectric and optical anisotropies using an anisotropic semiconducting vdW magnet, CrSBr twisted bilayers (tBLs) with twist angle ranging from 0° to 90°, as a model system. We found the huge binding energy and quasi-1D nature of excitons maintain while the linear dichroism of excitons can be continuously tuned between zero and unity with twist angles up to 90°. The insights from this work benefit fundamental studies on 2D vdW materials and applications like nano-optics, twistronics, and spintronics.