Dynamics of vortex processes in thin-film bridge structures made of high Tc superconductors

Dynamic rf effects in bridge structures made of thin films of high Tc superconductors have been studied experimentally. The resistive state of such structures stems from the motion, driven by the Lorentz force, of magnetic flux quanta (vortices), whose shape in granular high Tc superconductors differs from that of Abrikosov or Josephson vortices. Experiments have been carried out on the narrow-band excitation of electromagnetic waves in bridge structures and on the locking of this excitation process by an external signal. The excitation and the locking are observed in the course of coherent motion of vortices under conditions of weak pinning. If the pinning is instead very strong, structural features are seen on the plot of the impedance of the structure versus the static electric field. The experimental results are compared with the predictions of existing theoretical models