Tunability of multiple ultraflat bands and effect of spin-orbit coupling in twisted bilayer transition metal dichalcogenides

Abstract

Ultraflat bands that have been theoretically and experimentally detected in a bunch of van der Waals stacked materials show some peculiar properties, for instance, highly localized electronic states and enhanced electron-electron interactions. In this Rapid Communication, using an accurate tight-binding model, we study the formation and evolution of ultraflat bands in transition metal dichalcogenides (TMDCs) under low rotation angles. We find that, unlike in twisted bilayer graphene, ultraflat bands exist in TMDCs for almost any small twist angles and their wave function becomes more localized when the rotation angle decreases. Lattice relaxation, pressure, and local deformation can tune the width of the flat bands, as well as their localization. Furthermore, we investigate the effect of spin-orbit coupling on the flat bands and discover spin/orbital/valley locking at the minimum of the conduction band at the $K$ point of the Brillouin zone. Ultraflat bands found in TMDCs with a range of rotation angle below ${7}^{\ensuremath{\circ}}$ may provide an ideal platform to study strongly correlated states.