Superconductivity in 5 d transition metal Laves phase SrIr 2

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 micro 0 H c1 and upper critical field micro 0 H c2, coherence length xi(0), penetration depth lambda(0) and Ginzburg-Landau (GL) parameter kappa(0) are approximately micro 0 H c1 = 101 Oe, micro 0 H c2(0) = 5.9 T, xi(0) = 7.47 nm, lambda(0) = 237 nm, and kappa(0) = 31.7, respectively. The specific-heat data indicate that SrIr2 is a strong-coupling superconductor because the value of DeltaC/gammaT 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.