Tunneling in graphene–topological insulator hybrid devices

Abstract

Hybrid graphene–topological insulator (TI) devices were fabricated using a mechanical transfer method and studied via electronic transport. Devices consisting of bilayer graphene (BLG) under the TI Bi[subscript 2]Se[subscript 3] exhibit differential conductance characteristics which appear to be dominated by tunneling, roughly reproducing the Bi[subscript 2]Se[subscript 3] density of states. Similar results were obtained for BLG on top of Bi[subscript 2]Se[subscript 3], with tenfold greater conductance consistent with a larger contact area due to better surface conformity. The devices further show evidence of inelastic phonon-assisted tunneling processes involving both Bi[subscript 2]Se[subscript 3] and graphene phonons. These processes favor phonons which compensate for momentum mismatch between the TI Γ and graphene K,K[superscript ′] points. Finally, the utility of these tunnel junctions is demonstrated on a density-tunable BLG device, where the charge neutrality point is traced along the energy-density trajectory. This trajectory is used as a measure of the ground-state density of states.