Power dependence of microwave Z/sub s/ in high-T/sub c/ Josephson junctions: Measurements and modeling

The nonlinear power dependence of the microwave frequency surface impedance of high-T/sub c/ superconductors remains inadequately understood, thus limiting device applications. It is believed that weak links, grain boundaries, and other material defects exhibiting Josephson junction behavior are a source of the nonlinear behavior. Using a stripline-resonator technique, we have performed microwave measurements of the resistive and reactive components of the impedance as a function of input power, frequency, temperature, and dc applied magnetic field. The results are compared to a resistively shunted junction (RSJ) model that yields excellent agreement at low and intermediate values of the input current. The values of I/sub c/ and R/sub n/ from dc transport measurements are compared to the rf values obtained from fitting data using the RSJ model.