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

Abstract

Using a multiscale computational approach, we probe the origin and evolution of ultraflatbands in moir\'e superlattices of twisted bilayer MoS$_2$, a prototypical transition metal dichalcogenide. Unlike twisted bilayer graphene, we find no unique magic angles in twisted bilayer MoS$_2$ for flatband formation. Ultraflatbands form at the valence band edge for twist angles ($\theta$) close to 0$^\circ$ and at both the valence and conduction band edges for $\theta$ close to 60$^\circ$, and have distinct origins. For$ \theta$ close to 0$^\circ$, inhomogeneous hybridization in the reconstructed moir\'e superlattice is sufficient to explain the formation of flatbands. For $\theta$ close to 60$^\circ$, 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 ultraflatbands 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 realisation of ordered quantum dot array.