Tunneling spectroscopy of graphene nanodevices coupled to large-gap superconductors

We performed tunneling spectroscopy measurements of graphene coupled to niobium/niobium-nitride superconducting electrodes. Due to the proximity effect, the graphene density of states depends on the phase difference between the superconductors and exhibits a hard induced gap at zero phase, consistent with a continuum of Andreev bound states. At energies larger than the superconducting gap, we observed phase-dependent energy levels displaying the Coulomb blockade effect, which are interpreted as arising from spurious quantum dots, presumably embedded in the heterostructures and coupled to the proximitized graphene.United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0001819)Gordon and Betty Moore Foundation (Grant GBMF4541