Identification and modeling of microwave loss mechanisms in YBa2Cu3O7-x

It has been proposed that the nonlinear microwave response of YBa2Cu3O7-x thin films is due to small- or large-angle grain boundaries which behave as weak links, To identify dominant loss mechanisms in the measured response of stripline resonators, the relative change in surface reactance and resistance, r = Delta X-S/Delta R-S, is used as a characteristic 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, frequencies, and temperatures, In addition, a coupled-grain/RSJ model has been augmented to include Josephson currents up to and beyond the critical currents J(cj) of the weak links, The model can account for a distribution of grain and boundary properties including ICRn products, junction capacitances, and grain dimensions. The r-values predicted by the model are discussed and compared to measurements.