Tunneling in graphene-topological insulator hybrid devices

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 Bi₂Se₃ exhibit differential conductance characteristics which appear to be dominated by tunneling, roughly reproducing the Bi2Se3 density of states. Similar results were obtained for BLG on top of Bi2Se3, 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 Bi2Se3 and graphene phonons. These processes favor phonons which compensate for momentum mismatch between the TI Γ and graphene K,K′ 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.