Measurements and modeling of the microwave impedance in high-Tc grain-boundary Josephson junctions:: Fluxon generation and rf Josephson-vortex dynamics

Measurements and modeling of the microwave-frequency (rf) power dependence of the impedance in Y-Ba-Cu-O thin-film grain-boundary Josephson junctions (JJ's) are presented. Microwave impedance measurements were performed using a stripline resonator with an engineered grain-boundary JJ as a function of rf current (10(-4)-1 A) and temperature (5-70 K). To understand the observed power dependence, we have developed a long-junction model which allows for Josephson-vortex creation, annihilation, and motion. The impedance calculated using the long-junction model fits the measured data qualitatively. We show that Josephson vortices generated by the rf fields cause nonlinearities in the impedance, resulting in increases in both resistance and reactance with steps in the resistance due to flux quantization. These observations and analysis of Josephson-vortex effects at microwave frequencies have important implications for understanding rf power handling in high-T-c films.