Observation of Individual Josephson Vortices in YBCO Bicrystal Grain-boundary Junctions

摘要

The response of YBCO bicrystal grain-boundary junctions to small dc magneticfields (0 - 10 Oe) has been probed with a low-power microwave (rf) signal of4.4 GHz in a microwave-resonator setup. Peaks in the microwave loss at certaindc magnetic fields are observed that result from individual Josephson vorticespenetrating into the grain-boundary junctions under study. The system ismodeled as a long Josephson junction described by the sine-Gordon equation withthe appropriate boundary conditions. Excellent quantitative agreement betweenthe experimental data and the model has been obtained. Hysteresis effect of dcmagnetic field is also studied and the results of measurement and calculationare compared.