Critical current fluctuations in graphene Josephson junctions

Abstract

AbstractWe have studied 1/f noise in critical current $$I_c$$ 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 $$\simeq 5$$ ≃ 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 $$v_{rf}$$ v rf at 600–650 MHz. We find 1/f critical current fluctuations on the order of $$\delta I_c/I_c \simeq 10^{-3}$$ δ I c / I c ≃ 10 - 3 per unit band at 1 Hz. The noise power spectrum of critical current fluctuations $$S_{I_c}$$ S I c measured near the Dirac point at large, sub-critical rf-carrier amplitudes obeys the law $$S_{I_c}/{I{_c}}^2 = a/f^{\beta }$$ S I c / I c 2 = a / f β where $$a\simeq 4\times 10^{-6}$$ a ≃ 4 × 10 - 6 and $$\beta \simeq 1$$ β ≃ 1 at $$f > 0.1$$ f > 0.1  Hz. Our results point towards significant fluctuations in $$I_c$$ I c originating from variation of the proximity induced gap in the graphene junction.