Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder

We investigated the effect of enhancement of superconducting transition temperature [Formula: see text] by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La [Formula: see text] Sn [Formula: see text] , Ca [Formula: see text] Rh [Formula: see text] Sn [Formula: see text] , Y [Formula: see text] Rh [Formula: see text] Sn [Formula: see text] , Lu [Formula: see text] Rh [Formula: see text] Sn [Formula: see text]; [Formula: see text] 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 [Formula: see text] in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with [Formula: see text] (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 [Formula: see text] (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 [Formula: see text] in respect to the bulk [Formula: see text] one and proposed a model that explains the [Formula: see text] behavior in the series of nonmagnetic skutterudite-related compounds.