POWER DEPENDENCE OF MICROWAVE Z(S) IN HIGH-T-C JOSEPHSON-JUNCTIONS - MEASUREMENTS AND MODELING

The nonlinear power dependence of the microwave frequency surface impe dance of high-T-c superconductors remains inadequately understood, thu s limiting device applications. It is believed that weak links, grain boundaries, and other material defects exhibiting Josephson junction b ehavior are a source of the nonlinear behavior. Using a stripline-reso nator technique, we have performed microwave measurements of the resis tive and reactive components of the impedance as a function of input p ower, frequency, temperature, and de applied magnetic held. The result s are compared to a resistively shunted junction (RSJ) model that yiel ds excellent agreement at low and intermediate values of the input cur rent. The values of I-c and R-n from dc transport measurements are com pared to the rf values obtained from fitting data using the RSJ model.