Assessment of the Energy Gaps in Graphene-h-BN Superlattices with a Hexagonal Boron Nitride Tunnel Barrier

Engineering and detecting an energy gap in graphene has been an active research field ever since the crystalline carbon layer was isolated from its bulk form, hoping for next-generation device applications. Graphene/hexagonal boron nitride (h-BN) heterostructure can serve as an ideal experimental platform for generating energy gaps, originated from either atomic- or nano-scale altercations within hexagonal graphene-h-BN superlattices. Here, we report direct assessment of the energy gaps formed not only at the charge neutrality (main Dirac) point but also at the mini-zone boundary (second Dirac point, SDP) defined by the close packing of graphene and h-BN lattices. With a planar tunneling scheme using thin h-BN as a tunnel barrier, we investigate the progression of the energy gaps at varying the length of graphene-h-BN superlattices and an external magnetic field, revealing that the energy gap at the SDP responds differently to external variants in a microscopic scale when comparing with the gap at the main Dirac point. In addition, many-body interactions play a major role in deciding energy-gap sizes in tightly aligned graphene-h-BN superlattices as the effect from the interactions diminish as the twist angle increases.