SPECIFIC-HEAT OF PBMO6S8 IN HIGH MAGNETIC-FIELD

In order to investigate the volume upper critical field of the Chevrel-phase superconductor PbMo6S8,, specific-heat measurements have been performed in magnetic fields up to 24.5 T. The superconducting transition temperature T-c of 14.3 ( +/- 0.1)K is suppressed by the maximum magnetic field to 10.1 ( +/- 0.3) K, which extrapolates to an upper critical field of 56 T (confirming measurements at fields up to 14 T). For a mixed state in the magnetic field a linear term gamma(m)T, related to the core states, is present in the electronic contribution to the specific heat. At a magnetic field of 24.5 T, gamma(m) amounts to 50% of the normal state value gamma of 6.5 mJ/K-2 g-at. By extrapolation, an upper critical field of 54 T can be derived.