Materials science and surface impedance Z(T,f,H) of Nb and YBCO and their quantitative modelling by the leakage current of weak links

Abstract

In Nb2O5-x junctions the critical Josephson current jcJ(T) is accompanied by a small leakage current jbl(1/Rbl) and hence the rf residual losses Rres caused by weak links are small. HTS in-plane weak links show very much reduced jcJ(0) values compared with theory and a large leakage current jbl of the order of jcJ owing to a high density of intermediate states in disordered HTS junction material. The finite Rres(T,f,H) is due to the finite normal conducting leakage current with Rbl(T<0.9Tc) constant of weak links at separations aJ, where the Rres(T) dependence is dominated by jcJ(T) jcJ(0)(1-T/Tc). Quantitative experiment-model agreement is obtained with measured values of aJ(0.2-20 µm), of Rbn(1000-1 n cm2) and of jcJ(10-107 A cm-2) with