Tunneling conductance in a gapped graphene-based superconducting structure: Case of massive Dirac electrons

The tunneling conductance in a NG/SG graphene junction in which the graphene was grown on a SiC substrate is simulated. The carriers in the normal graphene (NG) and the superconducting graphene (SG) are treated as massive relativistic particles. It is assumed that the Fermi energy in the NG and SG are EFN∼400 meV and EFS∼400 meV+U, respectively. Here U is the electrostatic potential from the superconducting gate electrode. It is seen that the Klein tunneling disappears in the case where a gap exist in the energy spectrum. As U→∞, the zero bias normalized conductance becomes persistent at a minimal value of G/G0∼1.2. The normalized conductance G/G0 is found to depend linearly on U with constant slope of α=2/(EFN−mvF2)∼7.4, where 2mvF2 is the size of the gap Δ opening up in the energy spectrum of the graphene grown on the SiC substrate. It is found that G/G0≅2+αU for potentials in the range −270 meV