Intrinsic pinning and dissipation at high current density in epitaxial thin films of YBa 2Cu 2O 7− y

Abstract

Dissipation in the mixed state of YBa 2Cu 3O 7− y under magnetic fields applied parallel and nearly parallel to the basal plane is studied by use of epitaxial thin film samples and a measurement system with angular precision of ∼0.02°. It is found that the dependence of resistivity on the relative angle between the field and current diminishes as the film thickness is decreased, indicating a tendency of approach to the two-dimensional limit. The anomalous peak in the angular dependence of resistivity at high current densities, which we reported in our previous paper, is further investigated. It is found that the phenomenon is most distinct in the transverse magnetoresistance geometry and high transport current densities, indicatiing that it is caused by a strong Lorentz force acting on the segment of a flux line parallel to the layers. We attribute the phenomenon to a thermally assisted depinning of flux line segment (parallel to the layers) out of the intrinsic pinning potential.