A microwave technique for characterization of SNS and grain-boundary junctions

We have utilized a magnetic field modulated microwave absorption technique for characterizing SNS and grain-boundary junctions. The technique is based on the measurements of the first derivative microwave absorption P, with respect to an applied magnetic field B at 9.5 GHz, as a function of dc magnetic B/sub dc/. A homodyne detection system is used. Due to flux quantization in a non-uniform junction a series of equally spaced microwave absorption lines can be observed for B/sub dc/ and, in strongly coupled junction cases, the dependence of I/sub c/ on magnetic field and temperature can be extracted. Both the intra-grain boundary in a melt-textured YBa/sub 2/Cu/sub 3/O/sub x/ bulk material and thin film single grain boundary junction (GBJ) YBa/sub 2/Cu/sub 3/O/sub x/ were investigated. The result of the measurements agrees with a model in which the grain boundary consists of several sub-junctions in parallel.<>