Origin and evolution of ultraflat bands in twisted bilayer transition metal dichalcogenides: Realization of triangular quantum dots

摘要

Using a multiscale computational approach, we probe the origin and evolution of ultraflat bands in moire superlattices of twisted bilayer MoS2, a prototypical transition metal dichalcogenide. Unlike twisted bilayer graphene, we find no unique magic angles in twisted bilayer MoS2 for flat-band formation. Ultraflat bands form at the valence band edge for twist angles (theta) close to 0 degrees and at both the valence and conduction band edges for theta close to 60 degrees, and have distinct origins. For theta close to 0 degrees, inhomogeneous hybridization in the reconstructed moire superlattice is sufficient to explain the formation of flat bands. For theta close to 60 degrees, additionally, local strains cause the formation of modulating triangular potential wells such that electrons and holes are spatially separated. This leads to multiple energy-separated ultraflat bands at the band edges closely resembling eigenfunctions of a quantum particle in an equilateral triangle well. Twisted bilayer transition metal dichalcogenides are thus suitable candidates for the realization of ordered quantum dot array.