Transition from Type-II to Type-I Superconductivity with Magnetic Field Direction

Abstract

We report on a new effect in superconductivity and demonstrate experimentally that, because of the correlation of the upper critical field $H_{c2\mathrm{}}$ with crystal directions in single-crystalline $\mathrm{Ta}\mathrm{N}$ samples (anisotropy effect), at certain fixed temperatures the material is a type-I superconductor near the [100] and a type-II superconductor near the [111] directions.