Defect-assisted tunneling spectroscopy of electronic band structure in twisted bilayer graphene/hexagonal boron nitride moiré superlattices

Abstract

We report the demonstration of defect-assisted tunneling spectroscopy of the electronic band structure in twisted bilayer graphene (tBLG)/hexagonal boron nitride ( h-BN) moiré superlattices in which the moiré period between the two graphene layers is close to that between the graphene and h-BN layers. We measured both the in-plane and vertical carrier transport in the tBLG/ h-BN van der Waals (vdW) tunneling device. The moiré periods were determined from the in-plane carrier transport measurements. The observed vertical tunneling transport characteristics indicated that resonant tunneling occurs from the graphite electrode to tBLG through localized defect states in the h-BN tunnel barrier. We observed multiple defect-assisted resonant tunneling trajectories, from which we derived the density of states (DOS) for tBLG. The obtained DOS has broad flatband features, in qualitative agreement with the theoretical predictions. Furthermore, we obtained three types of DOS, suggesting that we probed local band structures corresponding to AA, AB/BA, and domain wall sites in tBLG. Thus, defect-assisted tunneling spectroscopy has potential as a tool to determine the local band structures in twisted 2D vdW materials.