Microwave intermodulation products and excess critical current in YBa2Cu3O7-x Josephson junctions

Third-order intermodulation power generated by a Josephson junction in an YBa2Cu3O7-x microwave resonator is measured and compared to a calculation based on the resistively shunted junction model. The results agree with junction parameters determined by power-dependent loss measurements On the same resonator at temperatures near the transition temperature T-c, but measurements below T-c/2 suggest that excess critical current, which does not contribute to the nonlinear properties of the junction, occurs at lower temperatures. Local heating is suggested to explain this feature. These results are relevant to the coupled-grain model used to describe microwave properties of high-T-c superconductors and to the understanding of Josephson junctions in these materials. (C) 1996 American Institute of Physics.