Anisotropic flux pinning in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// single crystals

Direct transport measurements of the critical currents as well as their angular and field dependencies in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// single crystals were performed. The role of twin planes as extended defects, which provide a vortex locking, is studied and their contribution to the J/sub c/ anisotropy is analyzed. The angular dependence of the critical current is represented as a combination of a contribution from extended defects and a point-like-defect-induced anisotropic background. The latter is responsible for the major part of the measured J/sub c/ anisotropy. The observed Kramer-like scaling law concerning the dependencies of the volume pinning force versus the applied magnetic field component along the c-axis indicates a three-dimensional flux line lattice behavior and excludes vortex decoupling as a possible mechanism of the "fishtail-effect".<>