Observation of individual Josephson vortices in YBa 2 Cu 3 O 7¿d bicrystal grain-boundary junctions

The response of YBCO bicrystal grain-boundary junctions to small dc magnetic fields (0 - 10 Oe) has been probed with a low-power microwave (rf) signal of 4.4 GHz in a microwave-resonator setup. Peaks in the microwave loss at certain dc magnetic fields are observed that result from individual Josephson vortices penetrating into the grain-boundary junctions under study. The system is modeled as a long Josephson junction described by the sine-Gordon equation with the appropriate boundary conditions. Excellent quantitative agreement between the experimental data and the model has been obtained. Hysteresis effect of dc magnetic field is also studied and the results of measurement and calculation are compared. Grain-boundary junctions in high-temperature-superconducting (HTS) thin films have been studied extensively 1–9 due to their importance in both device applications and fundamental physics. The dynamics of Josephson vortices in Josephson junctions, which are analogous to the Abrikosov vortices in type II superconductors, 10,11 is a very interesting subject, because of the mesoscopic physics involved. Much effort has been devoted to understanding the collective behavior of Josephson vortices in situations such as flux-flow devices. 12 The study