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

High temperature superconductor (HTS) Josephson junctions usually show a la rge amount of low frequency 1/f noise. This 1/f noise is caused by fluctuat ions of the junction critical current I, and normal resistance R-n which ar e anti-phase correlated. These fluctuations originate from random fluctuati ons of the occupation number of charge traps in an insulating barrier. We h ave studied the magnetic field dependence of the normalized fluctuations in HTS grain boundary junctions to obtain information on possible spatial cor relations between individual traps. Our experiments suggest that there are no spatial correlations between the noise causing traps on a length scale l arger than a few 100 nm. Furthermore, the temperature and voltage dependenc e of the characteristic times of individual traps has been investigated. He re, for the first time we found clear evidence for a transition from a ther mally activated to a tunneling like behavior of individual traps at low tem peratures.