Transport Studies of Graphene/Hi-Tc Superconductor Junctions

Superconductor-graphene-superconductor (S-Gr-S) junctions have been well studied with low-temperature superconductors showing evidence of supercurrent and different Andreev reflection scenarios. We present the results of DC transport in an S-Gr-S junction made with a high-temperature superconductor, Bi₂Sr₂Ca₁Cu₂O_x (BSCCO), by mechanically cracking it and stacking it on exfoliated graphene in an inert environment. Due to the large superconducting gap and high upper critical field of BSCCO, we can study the properties of graphene/BSCCO interface over a wide range of parameters, including temperature, bias, doping, and magnetic field, over a robust set of values. We provide evidence of the Dirac nature of graphene at the superconducting junction. The properties of Andreev reflection can be clearly distinguished from the normal carrier transport, which is dominated by the transport properties of graphene.