Soft-phonon-mediated superconductivity in Ca₃(Ir_0:55Co_0:45)₄Sn₁₃ from specific heat, magnetization and resistivity

We report measurements of the DC magnetization, specific heat and electric resistivity of 45% Cobalt-doped Ca₃(Ir_0:55Co_0:45)₄Sn₁₃. The anomaly T* ≈ 38K reported in Ca₃Ir₄Sn₁₃ is suppressed to T_c in this 45% Cobalt-doped sample. The superconducting transition temperature is 7.3 K. The phonon density of states F(ω) and the spectral electron-phonon scattering function α²_trF(ω) are determined by deconvolution of the specific heat and resistivity curves, respectively. A dominant mode at 12meV appears in both histograms, which indicates that low-lying soft phonon modes, presumably related to the vicinity to the structural instability, are responsible for the superconductivity of Ca₃(Ir_0:55Co_0:45)₄Sn₁₃. This points to a conventional phonon-mediated origin of superconductivity in Ca₃Ir₄Sn₁₃, and rules out a magnetic spin fluctuation mediated pairing scenario.