Strong-coupling phonon-mediated scenario of superconductivity in C a3 i r4 S n13 and C a3(I r0.91 C o0.09)4 S n13

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(ω) and the spectral electron-phonon scattering function atr2F(ω) are determined by deconvolution of the specific heat and electrical resistivity, respectively. A dominant mode appears in both histograms at ℏω=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.