Upper critical field anisotropy in the Chevrel phase compound PbMo6S8

Abstract

The anisotropy of the upper critical field,H c2, was measured on deoxygenated single crystals of the Chevrel phase compound PbMo6S8. The superconducting transition temperature,T c, was determined with the applied field pointing in various directions in the hexagonal $$(2\overline 1 0)$$ plane. At a fixed value of the external field,T c is an oscillating function of direction. Since theH c2 versusT curve is linear in the field region we probed, the shape of the anisotropy inT c at constantH is the same as the anisotropy ofH c2 at constantT. The data reflect the low-temperature symmetry of the crystal structure. Two-fold symmetry was observed in the $$(2\overline 1 0)$$ plane. The data were fitted to the effective mass model with uniaxial symmetry. The anisotropy ofH c2 is more complex than that previously observed by us in Cu1.8Mo6S8. We relate this observation to the structural differences of these compounds.