Effect of Virtual Andreev Reflection on Tunneling in Normal/Superconductor Graphene Junction

The Andreev reflection (AR) process and the tunneling conductance in graphene-based normal metal/superconductor junction are studied, where both massless and massive fermions are considered. As a result, the evanescent type of AR or the virtual Andreev reflection (VAR), is found to take place at the interface above the critical angle or in case where AR decays due to massive energy gap. Significantly, current of the junction is found to exist in the evanescent AR regime. In this work, we modify tunneling conductance formalism by including the current induced by the evanescent type of AR process (or VAR), which has not been taken into account in previous studies. In contrast to the previous work, our formula leads to a new result due to the influence of the VAR when the energy of the quasiparticles greater than the superconducting gap.