Collective Motion of Vortices Induced by A.C. Magnetic Field in the High Anisotropy BSCCO

Abstract

The microwave dissipation induced by an ac magnetic field collinear to the dc magnetic field in the highly anisotropic BSCCO shows two signals. One, that occurs just below Tc in all superconductors, corresponds to changes in the microwave dissipation of the TAFF resistivity caused by a magnetic modulation. The other signal arises from a double frequency process, where the ac field prepares the vortex system to enable its interaction with the microwave. This signal whose response to the ac field is non-linear (NL) is studied in this work, mostly for the configuration where the dc and the ac magnetic field are parallel the a−b plane. We demonstrate that below Bdc=0.0025 T the ac field interacts with individual non-interacting vortices. Above Bdc=0.005 T, the ac induces simultaneously, collective motions of pinned vortices and Josephson unpinned vortices. The latter has a bell-shaped form and therefore can be identified as an oscillation mode induced by the magnetic microwave field. This oscillation mode is excited by the microwave magnetic field and therefore it differs from the Josephson plasma excitation mode or the vortex excitation mode where both are excited by the microwave electric field. Defects, high temperatures and high ac fields impedes the excitation of this mode. The results are discussed with respect to the “vortex shaking” effect and other experimental and theoretical results.