Enhancing superconductivity of the nonmagnetic quasiskutterudites by atomic disorder

Abstract

We investigated the effect of enhancement of superconducting transition temperature Tc by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La3 M4 Sn13, Ca3 Rh4 Sn13, Y5 Rh6 Sn18, Lu5 Rh6 Sn18; M = Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale ξ in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with Tc⋆ > Tc (dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of Tc⋆ ∼ 2Tc (dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase Tc⋆in respect to the bulk Tc one and proposed a model that explains the Tc⋆ > Tc behavior in the series of nonmagnetic skutterudite-related compounds.