Possible two-gap behavior in noncentrosymmetric superconductor Mg₁₀Ir₁₉B₁₆: A penetration depth study

We report measurements of the magnetic penetration depth λ(T) of Mg₁₀Ir₁₉B₁₆ down to 50 mK (<0.01T_c). We observe a sample-independent small second drop around 0.8 K and an overall low-temperature response that indicate a possible two-gap superconductivity in Mg₁₀Ir₁₉B₁₆. A two-isotropic-gap model can account for the present penetration depth data. However, the lack of inversion symmetry in this compound with the heavy transition element Ir may lead to a large antisymmetric spin-orbit coupling that splits the spin bands and mixes spin-singlet and spin-triplet states. A model based on the two spin-split bands, with nodeless anisotropic gaps and dominant spin-triplet components, can also explain the present results. The data rule out an isotropic spin-singlet gap structure, as suggested by specific-heat measurements.