Switching effect in a gapped graphene d-wave superconductor structure

Abstract

By depositing a d-wave superconductor (using proximity method) on the top of graphene grown on a substrate-induced bandgap (such as a SiC substrate), a d-wave superconductor caused by the massive Dirac electrons can be fabricated. Using the BTK theory, the tunneling conductance in a gapped graphene N/d-wave superconductor junction, where N is a normal gapped graphene, is studied. This work focuses on the influence of d-wave pairing on the conductance of the junction. In this result, for conductance G/GN plotted versus either the biased voltage V or the d-wave superconducting orientation angular α, a sharp conductance peak like an impulse function can be observed due to increasing the Dirac energy gap. The maximum conductance peak Gmax is also enhanced by increasing the electrostatic potential U in superconductor-electrode, giving rise to Gmax/GN=2 for increasing U → ∞. This sharp conductance peak occurs related to the condition of eV = Δ cos (2 α). The unit step conductance in this junction, G / GN = 2 Θ (U), is found for α = π / 4 and eV / Δ = 0 when EF - m vF2 → 0. This is unlike a unit step conductance in a gapped graphene N/s-wave superconductor junction which was recently observed for eV / Δ = 1. © 2009 Elsevier B.V. All rights reserved.