Low frequency voltage noise in high temperature superconductor Josephson junctions

We have performed detailed measurements of 1/f voltage noise in a variety of bicrystal grain boundary Josephson junctions and in ramp edge junctions with artificial barriers. Fluctuations of the junction critical current I/sub c/ and the normal state resistance R/sub n/ were found to fully account for the measured 1/f noise. For the normalized fluctuations S/sub I/ and S/sub R/, which were found to be independent of temperature, a linear scaling with R/sub n/ has been observed. Correlation experiments proved that the fluctuations of I/sub c/ and R/sub n/ are anti-phase correlated. The ratio S/sub I//S/sub R/ of the normalized fluctuations is in close agreement with the scaling of the I/sub c/R/sub n/-product indicating a common underlying physical mechanism. Our analysis strongly supports the Intrinsically Shunted Junction (ISJ) model based on an insulating grain boundary containing a high density of localized defect states with fluctuating electron occupation causing 1/f noise. The effective charge trapping time within single traps shows thermally activated behavior and was found to decay exponentially with increasing bias voltage.