Orientational Dependence of the Flux-Flow Resistivity and Critical Current Density in Type-II Superconducting Foils

Flux-flow measurements on type-II superconducting foils show that the Lorentz force is fully adequate to describe the angular dependence of the flux-flow resistivity. The orientational dependence of the critical-current density is not simply obtained, however, by assuming that flow begins when the Lorentz force achieves a critical value. Instead, the results imply an anisotropy in the pinning force which we interpret in terms of the natural anisotropy of the surface in a foil sample. The role of the surface in flux pinning is therefore emphasized again.