Coherent quantum transport in graphene-based normal metal-superconductor double junctions

Based on the transfer-matrix method, we have investigated the coherent quantum transport in a graphene-based normal metal-insulator-superconductor-insulator-normal metal (NG/IG/SG/IG/NG) double junctions with a barrier of thickness d and with a potential strength V0 applied across the barrier region. It is found that all the reflection coefficients in BTK theory as well as conductance spectra of such system oscillate with the external voltage and the barrier strength V0. The oscillation feature of conductance can be tuned largely by the thickness of the superconductor interlayer. These phenomena are essentially different from those found in conventional normal metal-superconductor double junctions. The physical origin for those phenomena has also been analyzed.