Anisotropy of the upper critical field and specific heat in V3Si - a superconductor with cubic symmetry

The specific heat of a V3Si single crystal (T-c = 17 K, H-c2 = 20 T) in mag netic fields up to 8 T is investigated experimentally for three orientation s of the field relative to the crystallographic directions Hi H\\[001], H\\ [110], and H\\[111]. Both the upper critical magnetic field and the specifi c heat of the mixed state are observed to depend on the orientation of the magnetic field relative to the crystallographic directions (anisotropy): Th e critical field reaches its maximum value and the specific heat its minimu m value in a field along the [001] direction. The anisotropy scale in both phenomena increases as the magnetic field and reaches 3% in a 6 T field. Th e interrelationship of the upper critical field anisotropy and the specific -heat anisotropy in type-II superconductors is studied. It is shown that th e anisotropy of the specific heat in the mixed state in weak fields can ser ve as a criterion for nontrivial pairing. (C) 1999 American Institute of Ph ysics. [S0021-3640(99)00601-5].