Superconducting Phase Diagram of Rh₁₇S₁₅

Rh₁₇S₁₅ (Miasite) is a 4d-electron metal which displays superconductivity below T_c = 5.4 K at zero field, with an upper critical field value B_c2 = 19.2 T at T = 0.07 K. Above T_c, Rh₁₇S₁₅ is a paramagnet. The crystallographic structure (Pm3m) of Rh17S15 features a nearest-neighbor Rh-Rh distance even less than in elementary (fcc) Rh, resulting in a high density of 4d-electron states at the Fermi level [1]. In our contribution, we report on measurements of the specific-heat and resistivity in fields up to 14 T and of the magnetic susceptibility in fields up to 20 T of a polycrystalline sample of Rh₁₇S₁₅. Our data allow us to map out the complete superconducting phase diagram. The existence of narrow 4d band states (and thus of strong electronic correlations that seem not to provide magnetic correlations) is supported by the found moderately high electronic contribution to the specific-heat of about 100 mJ/molK2 and favors the existence of a strong superconducting interaction. Together with the remarkably high upper critical field (exceeding the Pauli limit by a factor of two), these facts make Rh₁₇S₁₅ a likely candidate for unconventional superconductivity.