Anisotropy dominated radio frequency vortex dynamics in Bi₂Sr₂CaCu₂O₈ thick film on silver tapes

Abstract

Vortex dynamics at radio frequency (rf) is studied in flexible tape samples of Bi₂Sr₂CaCu₂O₈ superconductor as functions of dc magnetic field, temperature and orientation between the field and plane of the tape. The rf response in the geometry when the dc field is perpendicular to the tape suggests two distinct regimes of vortex dynamics, one corresponding to a moderately pinned three-dimensional vortex solid and the other a liquid of two-dimensional vortices. The rf penetration depth in the 3D pinned phase is analyzed in the framework of the theories of single vortex pinning and the behaviour of pinning force constant k_p is discussed. In the vortex solid phase we see evidence of flux lock-in between the CuO₂ planes. The angle dependent response in the liquid state scales with the component of dc field parallel to c-axis. The scaling analysis shows some renormalization of the anisotropy due to non-zero deviations from a perfect alignment of the grains parallel to the plane of the tape.