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

Abstract

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 E FN ∼ 400 meV and E FS ∼ 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 / G 0 ∼ 1.2 . The normalized conductance G / G 0 is found to depend linearly on U with constant slope of α = 2 / ( E FN − m v F 2 ) ∼ 7.4 , where 2 m v F 2 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 / G 0 ≅ 2 + α U for potentials in the range − 270 meV < U < 0 meV and G = 0 for potentials U < − 270 meV . As α → ∞ , the conductance for e V = Δ ( V is the bias voltage placed across the NG/SG junction) can be approximated by a unit step function G ( e V = Δ , U ) / G 0 ∼ 2 Θ ( U ) . This last behavior indicates that a NG/SG junction made with gapped graphene could be used as a nano switch having excellent characteristics.