  High-temperature superconductors (HTS) are finding use as high - current
wires for potential application in power devices. The dependence of their
basal-plane critical current properties on orientation in a magnetic field can
pose important design problems. Here we report material and operating parameter
conditions where prototype HTS tape conductors exhibit critical current
characteristics that are essentially field-orientation independent. The novel
phenomenon is observed for specific magnetic field intensities that depend on
the operating temperature, and in materials having strong flux pinning by
extended nanoscale structures aligned roughly along the HTS crystalline c-axis.
The effect can be described by a simple model for the field dependence of
critical current density, generalized for anisotropic electronic response. This
description may provide insight into means to fine-tune the material properties
for nearly isotropic performance characteristics at a preferred field and
temperature.
