Observation of individual Josephson vortices in YBa2Cu3O7-delta bicrystal grain-boundary junctions

The response of YBa2Cu3O7-delta bicrystal grain-boundary junctions to small de magnetic fields (0-10 Oe) has been probed with a low-power microwave (r f) signal of 4.4 GHz in a microwave-resonator setup. Peaks in the microwave loss at certain de magnetic fields are observed that result from individua l Josephson vortices penetrating into the grain-boundary junctions under st udy. The system is modeled as a long Josephson junction described by the si ne-Gordon equation with appropriate boundary conditions. Quantitative agree ment between the experimental data and the model has been obtained. The hys teresis effect of de magnetic field is also studied and the results of meas urement and calculation are compared.