Magnetic field and temperature specific isotropic critical currents in strong-pinning high-temperature superconductors

We report the observation of a unique temperature-dependent magnetic field, $H$*($T)$, at which the critical current of (R)BaCuO (R=rare earth) films with strong $c$-axis pinning can be nearly isotropic. That is, $J_{c}(\theta $, $H$*) $\cong $ constant over nearly the entire interval of sample orientation from \textit{H$\vert \vert $c} to \textit{H$\vert \vert $ab }(in the full Lorentz force configuration). The phenomenon is observed in classes of HTS coatings that contain self-assembled, strongly pinning columnar stacks of second-phase precipitates, BaZrO$_{3}$, oriented near the $c$ axis, and appears to originate from the combination of and offsetting effects of material anisotropies. Systematics of this behavior will be explored and several important control parameters will be identified.