LOW-FREQUENCY VOLTAGE NOISE IN HIGH-TEMPERATURE SUPERCONDUCTOR JOSEPHSON-JUNCTIONS

We have performed detailed measurements of 1/f voltage noise in a vari ety of bicrystal grain boundary Josephson junctions and in ramp edge j unctions with artificial barriers. Fluctuations of the junction critic al current I-c and the normal state resistance R-n were found to fully account for the measured 1/f noise. For the normalized fluctuations S -I and S-R, which were found to be independent of temperature, a linea r scaling with R-n has been observed. Correlation experiments proved t hat the fluctuations of I-c and R-n are anti-phase correlated. The rat io S-I/S-R of the normalized fluctuations is in close agreement with t he scaling of the IcRn-product indicating a common underlying physical mechanism. Our analysis strongly supports the Intrinsically Shunted J unction (ISJ) model based on an insulating grain boundary containing a high density of localized defect states with fluctuating electron occ upation causing 1/f noise. The effective charge trapping time within s ingle traps shows thermally activated behavior and was found to decay exponentially with increasing bias voltage.