Tuning the electronic structure and electron correlation in 2D twisted massive Dirac system: the case of twisted bilayer hBN

Recent experiments have suggested that twisted bilayer graphene (TBG) near magic angles can be an idea platform for the study of strong correlation effects and unconventional superconductivity. Interestingly, our density functional theory (DFT) calculations show that flat bands also develop at both the top of the valence bands and bottom of the conduction bands in bilayer hBN with a twist. But different from the case of TBG systems, the band width of these flat bands decreases monotonically with twist angles and there is no appearance of any magic angles. We further use functional renormalization group (FRG) method to show that the flat band at the top of the valence bands can host exotic strong-correlated physics, such as the appearance of Mott insulator phase and unconventional superconductivity. Our study suggests that the gapless and massless characters of graphene is not essential in the observed strong-correlated phenomena and many more other 2D materials can also be explored in the form of twisted bilayer system for the study of unconventional superconductivity.