Angular anisotropy of the upper critical field in YNi2B2C

The borocarbide series of materials exhibits a strong anisotropy in its superconducting characteristics such as the upper critical field and critical current. Until now, however, the complete angular dependency of the anisotropies has been lacking, reported only in the principal crystallographic directions. Measurements are presented here of both the out-of-plane and in-plane angular variation in the upper critical field made on epitaxial thin films of the non-magnetic borocarbide compound YNi2B2C. An unconventional behaviour is observed in the full out-of-plane anisotropy, previously unreported and therefore unconsidered by current theories. Within the basal plane, a weaker but still significant anisotropy is observed. A full understanding of this behaviour is required before the behaviour of the magnetic borocarbides can be properly interpreted