THE EFFECT OF TRAPPED FLUX UPON THE MAGNETIC-FIELD DEPENDENCE OF THE CRITICAL-CURRENT OF JOSEPHSON-JUNCTIONS

Measurements of the magnetic field dependence of the critical current I-c(B) of Josephson junctions, involving high temperature superconduct ors, often give evidence that the supercurrents are spatially non-unif orm. However, flux trapping can complicate the interpretation of I-c(B ) curves. A model has been developed for the behavior of SNS type junc tions in a trilayer geometry containing trapped flux. We have investig ated, using this model, combined with simulations, how the features of the I-c(B) curve change as the number of trapped fluxlines increases. For a uniform junction, flux-trapping distorts the I-c(B) curve and s uppresses the maximum critical current by 1/root N-f where N-f is the number of fluxlines. The effect of trapped flux on current density cor relation functions derived using the Wiener-Khinchine theorem from I-c (B) curves has also been investigated and is described. In addition we discuss the relevance of the model to planar geometries.