Charge redistribution and interlayer coupling in twisted bilayer graphene under electric fields

There is an ongoing controversy on the electronic characteristics of rotated bilayer graphene. Several experiments on rotated few-layer graphene grown on SiC show an electronic behavior similar to that of single-layer graphene, with the same carriers' velocity as that of an isolated graphene monolayer; for this reason, these systems have been considered as composed of uncoupled graphene sheets. We investigate the electronic density redistribution of rotated bilayer graphene under a perpendicular electric field, showing that the layers are actually coupled even for large angles. This layer-layer coupling is evidenced by the charge transfer on these structures as a function of the external voltage. We find an inhomogeneous excess charge distribution that is related to the moir\'e patterns for small angles, but that persists for larger angles where the carriers' velocity is equal to that of single layer graphene. Our results show that rotated bilayer systems are coupled for all rotation angles.