Strong-coupling phonon-mediated scenario of superconductivity in Ca3Ir4Sn13 and Ca3(Ir0.91Co0.09)4Sn13.

We report measurements of the specific heat and electrical resistivity of Ca3(Ir0.91Co0.09)4Sn13 in comparison to Ca3Ir4Sn13. The Co substitution was chosen to suppress the structural anomaly T*=38K reported in Ca3Ir4Sn13. While the superconducting transition temperature of Ca3(Ir0.91Co0.09)4Sn13 is slightly higher than in the stoichiometric parent compound Ca3Ir4Sn13, and it displays a stronger superconducting coupling strength, the absence of a structural phase transition allows us to determine the spectral distribution of phonon states and its relation to superconductivity. The phonon density of states F(w) and the spectral electron-phonon scattering function atr²F(w) are determined by deconvolution of the specific heat and electrical resistivity, respectively. A dominant mode appears in both histograms at hw=12meV, which indicates that this phonon mode is responsible for the superconductivity in Ca3(Ir0.91Co0.09)4Sn13. The data suggest that superconductivity in this material class can be conclusively explained within a conventional strong -coupling phonon-mediated scenario. [ABSTRACT FROM AUTHOR]