IDENTIFICATION AND MODELING OF MICROWAVE LOSS MECHANISMS IN YBA2CU3O7-X

It has been proposed that the nonlinear microwave response of YBa2Cu3O 7-x thin films is due to small- or large-angle grain boundaries which behave as weak links, To identify dominant loss mechanisms in the meas ured response of stripline resonators, the relative change in surface reactance and resistance, r = Delta X-S/Delta R-S, is used as a charac teristic signature for the different mechanisms, We show that Meissner state and flux flow losses can be differentiated from hysteresis loss for a variety of films across a range of microwave powers, frequencie s, and temperatures, In addition, a coupled-grain/RSJ model has been a ugmented to include Josephson currents up to and beyond the critical c urrents J(cj) of the weak links, The model can account for a distribut ion of grain and boundary properties including ICRn products, junction capacitances, and grain dimensions. The r-values predicted by the mod el are discussed and compared to measurements.