Magnetic field-orientation independence of large basal-plane critical currents in RBCO films with correlated pinning nanostructure*

It has been widely confirmed that self-assembled columnar stacks of second-phase precipitates aligned near to the $c-$axis provide strong flux pinning in RBCO epitaxial films. Such growth-controlled nanostructures can be produced by at least two different deposition techniques and for several species of oxide precipitates. For many of these systems, the usual dependence of in-plane critical current densities, $J_{c}$, on field-orientation nearly vanishes at a specific temperature-dependent field, $B$*($T)$. The phenomenon can be described by a competition between intrinsic electronic anisotropy and orientation-dependent pinning. A simple model parameterizes the effect through the dependencies $H_{irr}(\theta )$ and the power-law decay exponent $\alpha (\theta )$, where $J_{c} \quad \propto $ $H^{-\alpha }$ in the intermediate field regime. Limits to and fundamental aspects of the model with respect to these parameters will be discussed.