Above-gap Conductance Anomaly Studied in Superconductor-Graphene-Superconductor Josephson Junctions

We investigated the electrical transport properties of superconductor-graphene-superconductor (SGS) Josephson junctions. At low voltage bias, we observed the conventional proximity-coupled Josephson effect, such as supercurrent flow through graphene, a sub-gap structure of differential conductance due to Andreev reflection, and a periodic modulation of the critical current; I,. when a perpendicular magnetic field H is applied to the graphene. For high bias above the superconducting gap voltage, however, we observed an anomalous jump of the differential conductance, the voltage position of which is sensitive to the backgate voltage V-g. Our extensive study with varying temperature, and H reveals that the above-gap structure takes place at a characteristic power P* irrespective of V-g, for a given junction. The temperature and the H dependences of P* are well explained by an increase in the electron temperature in graphene.