MEASUREMENTS AND MODELING OF THE MICROWAVE IMPEDANCE IN HIGH-T-C GRAIN-BOUNDARY JOSEPHSON-JUNCTIONS - FLUXON GENERATION AND RF JOSEPHSON-VORTEX DYNAMICS

Measurements and modeling of the microwave-frequency (rf) power depend ence 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-boundar y 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 lon g-junction model which allows for Josephson-vortex creation, annihilat ion, and motion. The impedance calculated using the long-junction mode l fits the measured data qualitatively. We show that Josephson vortice s generated by the rf fields cause nonlinearities in the impedance, re sulting in increases in both resistance and reactance with steps in th e resistance due to flux quantization. These observations and analysis of Josephson-vortex effects at microwave frequencies have important i mplications for understanding rf power handling in high-T-c films.