Sharp increase of microwave absorption due to shaking of Josephson vortices in BiSCCO superconductor

We study microwave (9.36 GHz) dissipation in the layered, highly anisotropic superconductors Bi2212 and Bi2223 subjected to a constant magnetic field parallel to the layers. The signal has a characteristic magnetic field dependence, increasing linearly at small fields, reaching a maximum, and decreasing at large fields. We demonstrate experimentally that the microwave absorption is strongly enhanced by application of a low frequency ac magnetic field parallel to the static field. The results are interpreted in the framework of Josephson phase electrodynamics in layered superconductors. In particular, the enhancement is explained as a result of the depinning of the Josephson vortices by the ac field shaking. The theoretical dc field dependence of the microwave absorption for Hdc Hac is in good agreement with experiment. The magnitude of the microwave signal increases rapidly with the anisotropy of the superconductor.