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_c and the normal state resistance R_n were found to fully account for the measured 1/f noise. For the normalized fluctuations Sr and SR which were found to be independent of temperature a linear scaling with Rn has been observed. Correlation experiments proved that the fluctuations of Ic and Rn are anti-phase correlated. The ratio ST/SR of the normalized fluctuations is in close agreement with the scaling of the IcRn-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.