Superconductivity in the Cu(Ir_1-xPt_x) ₂Se₄ spinel

We report the observation of superconductivity in the CuIr ₂Se₄ spinel induced by partial substitution of Pt for Ir. The optimal doping level for superconductivity in Cu(Ir_1-xPt _x)₂Se₄ is x = 0.2, where T_c is 1.76 K. A superconducting T_c vs composition dome is established between the metallic, normal conductor CuIr₂Se₄ and semiconducting CuIrPtSe₄. Electronic structure calculations show that the optimal T_c occurs near the electron count of a large peak in the calculated electronic density of states and that CuIrPtSe₄ is a band-filled insulator. Characterization of the superconducting state in this heavy metal spinel through determination of ΔC/γT_c indicates that it is BCS-like. The relatively high upper critical field at the optimal superconducting composition [H_c2(0) = 3.2 T] is much larger than that reported for analogous rhodium spinels and is comparable to or exceeds the Pauli field (μ₀H_P), suggesting that strong spin-orbit coupling may influence the superconducting state. Further, comparison to doped CuIr₂S₄ suggests that superconductivity in iridium spinels is not necessarily associated with the destabilization of a charge-ordered spin-paired state through doping.