Isotropic critical currents in anisotropic superconductors: a simple physical model

Critical current densities, $J_{c}$, that are nearly independent of magnetic field orientation can be observed in intrinsically anisotropic high-temperature superconductors that have specific, very strong flux pinning nanostructure. The phenomenon is observed to occur at specific temperature dependent fields, $H$*($T)$. The possibility of such isotropic behavior can be described by a simple physical model based on the orientation dependence of the irreversibility field $H_{irr}(\theta)$ and the power-law decay exponent $\alpha (\theta )$, where $J_{c}\propto H^{-\alpha }$ in the intermediate field regime. An analysis will be discussed that elucidates necessary conditions for occurrence of the effect, and provides possible predictive tools for tailoring of $H$*($T)$ to practical fields and temperatures by means of defect engineering.