Particle-size and temperature dependence of microwave noise in superconducting YBa2Cu3O/sub 7-//sub y/: Evidence for random Josephson junctions

The effects of particle size and temperature on the microwave noise and low-field microwave absorption in YBa2Cu3O/sub 7-//sub y/ powders have been studied by the magnetically modulated microwave absorption technique. The results can be interpreted in terms of a network of random Josephson junctions in the individual superconducting grains but are not consistent with the thermally activated flux creep model. An estimate of the size of the Josephson junctions is also obtained from the variation of the microwave noise with particle size