Flat Bands in Twisted Bilayer Transition Metal Dichalcogenide with Strong Spin-orbit Interaction

Since the discovery of flat bands at magic angle in twisted bilayer graphene, the formation of flat bands has been predicted for several other twisted bilayers, especially twisted transition metal dichalcogenides. We study the effect of spin-orbit coupling on the formation of flat bands in twisted WSe₂, which possesses strong spin-orbit interaction. The spin-orbit interaction affects the flat bands with twist angle close to 0° differently than those near 60°. The flat bands at valence and conduction band edge arise from K and Q points of the unit cell Brillouin zone respectively. For twist angle near 60°, we find that the flattening of the bands arising from K point is a result of the atomic reconstruction in the individual layers and not due to interlayer coupling. On the other hand, for twist angle close to 0°, the interlayer interaction between the two layers becomes important. Additionally, we also find flat bands folded from the Γ point of the unit cell Brillouin zone. The wave function localization of the flat bands matches well with STM measurements from existing literature [1]. Furthermore, we find that the atomistic spin-orbit splitting in moiré remains unchanged from the monolayer.
Reference:
1. Z. Zhang et al. Nat. Phys. doi:10.1038/s41567-020-0958-x (2020)