Superconductivity in 5d transition metal Laves phase SrIr₂

We report here the superconducting properties of a Laves phase superconductor SrIr₂, which has a cubic MgCu₂ structure. SrIr₂ is a type-II superconductor, with a T _c of 5.9 K. The estimated superconducting parameters of lower critical field µ ₀ H _c1 and upper critical field µ ₀ H _c2, coherence length ξ(0), penetration depth λ(0) and Ginzburg-Landau (GL) parameter κ(0) are approximately µ ₀ H _c1 = 101 Oe, µ ₀ H _c2(0) = 5.9 T, ξ(0) = 7.47 nm, λ(0) = 237 nm, and κ(0) = 31.7, respectively. The specific-heat data indicate that SrIr₂ is a strong-coupling superconductor because the value of ΔC/γT _c is approximately 1.71, which is larger than the value of 1.43 that is expected from the BCS theory. The physical properties obtained in this study are explained well by theoretical calculations including spin-orbit coupling (SOC). This result indicates that the physical properties of SrIr₂ are strongly affected by the presence of SOC.