Graphene-based Josephson junctions: phase diffusion, effects of magnetic field, and mesoscopic properties.

Abstract

We report on graphene-based Superconductor-Normal metal-Superconductor Joseph- son junctions with contacts made from lead. The high transition temperature of this superconductor allows us to observe the supercurrent branch at temperatures up to 􏰆 2 K. We are able to detect a small, but non-zero, resistance despite the Josephson junctions being in the superconducting state. We attribute this resistance to the phase diffusion regime, which has not been yet identified in graphene. By measuring the resistance as a function of temperature and gate voltage, we can further charac- terize the nature of electromagnetic environment and dissipation in our samples. In addition we modulate the critical current through grapehene by an external magnetic field; the resulting Fraunhofer interference pattern shows several periods of oscilla- tions. However, deviations from the perfect Fraunhofer pattern are observed, and their cause is explained by a simulation that takes into account the sample design.