Strong-coupling phonon-mediated scenario of superconductivity inCa3Ir4Sn13andCa3(Ir0.91Co0.09)4Sn13

We report measurements of the specific heat and electrical resistivity of $\mathrm{C}{\mathrm{a}}₃{(\mathrm{I}{\mathrm{r}}_0.91\mathrm{C}{\mathrm{o}}_0.09)}₄\mathrm{S}{\mathrm{n}}₁₃$ in comparison to $\mathrm{C}{\mathrm{a}}₃\mathrm{I}{\mathrm{r}}₄\mathrm{S}{\mathrm{n}}₁₃$. The Co substitution was chosen to suppress the structural anomaly ${T}^*=38\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ reported in $\mathrm{C}{\mathrm{a}}₃\mathrm{I}{\mathrm{r}}₄\mathrm{S}{\mathrm{n}}₁₃$. While the superconducting transition temperature of $\mathrm{C}{\mathrm{a}}₃{(\mathrm{I}{\mathrm{r}}_0.91\mathrm{C}{\mathrm{o}}_0.09)}₄\mathrm{S}{\mathrm{n}}₁₃$ is slightly higher than in the stoichiometric parent compound $\mathrm{C}{\mathrm{a}}₃\mathrm{I}{\mathrm{r}}₄\mathrm{S}{\mathrm{n}}₁₃$, 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 $F$(\ensuremath{\omega}) and the spectral electron-phonon scattering function ${{a}_tr}²F(\ensuremath{\omega})$ are determined by deconvolution of the specific heat and electrical resistivity, respectively. A dominant mode appears in both histograms at $\ensuremath{\hbar}\ensuremath{\omega}=12\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$, which indicates that this phonon mode is responsible for the superconductivity in $\mathrm{C}{\mathrm{a}}₃{(\mathrm{I}{\mathrm{r}}_0.91\mathrm{C}{\mathrm{o}}_0.09)}₄\mathrm{S}{\mathrm{n}}₁₃$. The data suggest that superconductivity in this material class can be conclusively explained within a conventional strong -coupling phonon-mediated scenario.