Analysis of the low-field microwave absorption line shape differences in YBa2Cu3Ox and Bi2Sr2CaCu2Ox superconductors

The field-dependent low-field microwave absorption for YBa2Cu3Ox (123) and Bi2Sr2CaCu2Ox (2212) superconducting powders and a 2212 crystal was investigated as a function of temperature and magnetic field modulation amplitude. The 2212 samples do not show a significant magnetic field sweep hysteresis while the 123 samples show a hysteresis strongly dependent on temperature and modulation amplitude. The microwave absorption line shapes for all samples, including the signals exhibiting strong hysteretic behavior, can be well simulated by a model for the microwave loss in intergranular Josephson junctions involving boundary and microwave-induced currents. The calculation allow an estimate of the average Josephson junction length to be about half the average grain size observed by scanning electron microscopy. Interpretation based on the assumptions in the line shape model indicates that the Josephson junctions are more weakly coupled in 2212 than in 123 superconductors