Properties of doubly-aligned graphene/boron nitride heterostructures*

A long-wavelength superlattice moiré potential emerges in heterostructures of graphene and boron nitride (BN) with small interlayer twist. The bandstructure of graphene is substantially modified by this superlattice potential, with secondary Dirac cones emerging at finite energy and band gaps opening at both the original and secondary Dirac points. We investigate the behavior of BN-encapsulated graphene in which the bottom BN is aligned to the graphene and the top BN can be rotated freely. We observe a significant enhancement of the band gap at the Dirac point in the case where both the top and bottom BN layers are perfectly aligned to the graphene. Additionally, while rotations of 60° are equivalent in typical graphene on BN heterostructures, we observe symmetry under 120° rotations of the top BN in our doubly-aligned devices, owing to the inequivalence of the boron and nitrogen potentials in the BN unit cell. In particular, we find the resistance of the Dirac point at room temperature is enhanced with the top BN at 0° but suppressed at 60°.