Correlation of critical current and resistance fluctuations in bicrystal grain boundary Josephson junctions

We have performed a detailed analysis of the low frequency 1/f noise in YBa₂Cu₃O_7-δ and Bi₂Sr ₂CaCu₂O_8+x grain boundary Josephson junctions (GBJs) fabricated on SrTiO₃ bicrystal substrates. The normalized fluctuation of the critical current, δI_c/I_c, and the normal resistance, δR_n/R_n were found to be almost independent of temperature and the misorientation angle. Furthermore, the magnitude of the fluctuations is very similar for both high-T_c cuprates. Correlation experiments showed that the fluctuations of I_c and R_n are anti-correlated. Our analysis strongly suggests that the source of 1/f noise in high-T_c bicrystal GBJs are localized defect states in an insulating grain boundary barrier with fluctuating electron occupation. The effective charge trapping time within single traps was found to decay exponentially with increasing bias voltage.