Observation of nonsinusoidal current-phase relation in graphene Josephson junctions

The current-phase relation of a Josephson junction can reveal valuable information about the processes influencing the supercurrent. In this paper we present direct measurements of the current-phase relation for Josephson junctions having a graphene barrier, obtained by a phase-sensitive SQUID interferometry technique. We find that the current-phase relation is forward skewed with respect to the commonly observed sinusoidal behavior for short junctions in the quasiballistic transport regime, consistent with predictions for the behavior of Dirac fermions in a Josephson junction. The skewness increases with critical current and decreases sharply with increasing temperature.