Critical current fluctuations in graphene Josephson junctions

We have studied 1/ f noise in critical current I c in h-BN encapsulated monolayer graphene contacted by NbTiN electrodes. The sample is close to diffusive limit and the switching supercurrent with hysteresis at Dirac point amounts to ≃ 5 nA. The low frequency noise in the superconducting state is measured by tracking the variation in magnitude and phase of a reflection carrier signal v rf at 600–650 MHz. We find 1/ f critical current fluctuations on the order of δ I c / I c ≃ 10 - 3 per unit band at 1 Hz. The noise power spectrum of critical current fluctuations S I c measured near the Dirac point at large, sub-critical rf-carrier amplitudes obeys the law S I c / I c 2 = a / f β where a ≃ 4 × 10 - 6 and β ≃ 1 at f > 0.1 Hz. Our results point towards significant fluctuations in I c originating from variation of the proximity induced gap in the graphene junction.