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Possible two-gap behavior in noncentrosymmetric superconductor Mg10 Ir19 B16: A penetration depth study

Abstract:

We report measurements of the magnetic penetration depth λ (T) of Mg10 Ir19 B16 down to 50 mK (<0.01 Tc). 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 Mg10 Ir19 B16. 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. © 2009 The American Physical Society.