Characterization of individual noise sources in high-temperature superconductor Josephson junctions

High temperature superconductor (HTS) Josephson junctions usually show a large amount of low frequency 1/f noise. This 1/f noise is caused by fluctuations of the junction critical current I/sub c/ and normal resistance R/sub n/ which are anti-phase correlated. These fluctuations originate from random fluctuations of the occupation number of charge traps in an insulating barrier. We have studied the magnetic field dependence of the normalized fluctuations in HTS grain boundary junctions to obtain information on possible spatial correlations between individual traps. Our experiments suggest that there are no spatial correlations between the noise causing traps on a length scale larger than a few 100 nm. Furthermore, the temperature and voltage dependence of the characteristic times of individual traps has been investigated. Here, for the first time we found clear evidence for a transition from a thermally activated to a tunneling like behavior of individual traps at low temperatures.