SPECIFIC-HEAT MEASUREMENTS OF PRESSURE-INDUCED REENTRANT SUPERCONDUCTIVITY IN EU0.9HO0.1MO6S8

Specific heat measurements of Eu0.9Ho0.1Mo6S8 were performed using an ac calorimetry technique under the extreme conditions of low temperature, high magnetic field, and hydrostatic pressure. The title compound is a Chevrel phase material, which is paramagnetic at ambient pressure, becomes superconducting for pressures above 7 kbar, and has a reentrant upper critical field [dHc2(T)/dT>0, as T --> 0 K]. Evidence that this material also has a high field-induced superconducting phase at low temperatures (H > 5 T, T < 1 K) was previously reported. The present ac calorimetry study carried out for 0.15 less-than-or-equal-to T less-than-equal-to 6 K, 0 less-than-or-equal-to H less-than-or-equal-to 20 T, and P congruent-to 8 kbar, shows a sharp superconducting transition for T < 1 K in the specific heat, which broadens at higher fields and temperatures. The results are analyzed to obtain a reentrant phase in agreement with previous transport work, but direct evidence for the high field-induced phase was not found. The mechanism for the field and temperature dependence of the superconductivity of Eu0.9Ho0.1Mo6S8 is discussed.