Indirect-to-direct bandgap transition in bilayer InSe: Roles of twistronics

We report a general approach to trigger indirect-to-direct bandgap transition in twisted bilayer two-dimensional (2D) systems. By performing first-principles density functional theory calculation, this indirect-to-direct bandgap transition is demonstrated to be realized in twisted bilayer InSe (tbIS). Through analyzing the spatial distribution of wave functions with respect to variations of twist angles, it is found that the shift of location of valence band maximum arises from the formation of Moiré flat bands associated with the evolution of electronic localization. Meanwhile, the relaxation effect introduced by out-plane displacement in relaxed tbIS Moiré superlattice is inevitable when considering the twist-angle dependent electronic properties. Our prediction in tbIS systems could provide an alternative strategy to realize indirect-to-direct bandgap transition through twistronics for designing nano-electronic devices.