Evidence for incompressible states in a metal-graphene tunnel junction in high magnetic field

Abstract

We present transport measurements of tunnel junctions made between Cu and graphene in a magnetic field. We observe a transition to a Landau-level-like structure at high fields, as well as a set of sharp features in the tunneling spectra that shift with gate and tunnel probe voltage along the lines of constant charge density. We explain the sharp features with the formation of degeneracy-split localized Landau levels and the addition of electrons to those levels one by one. A large capacitive coupling to the tunnel probe also increases the gate voltage spacing between the Landau levels.