${}^{119}$Sn-NMR investigations on superconducting Ca${}_3$Ir${}_4$Sn${}_{13}$: Evidence for multigap superconductivity

We report bulk superconductivity (SC) in Ca${}_3$Ir${}_4$Sn${}_{13}$ by means of ${}^{119}$Sn nuclear magnetic resonance (NMR) experiments. Two classical signatures of BCS superconductivity in spin-lattice relaxation rate ($1\mathrm{/}{T}_1$), namely the Hebel-Slichter coherence peak just below the $T_c$ and the exponential decay in the superconducting phase, are evident. The noticeable decrease of ${}^{119}$Sn Knight shift below $T_c$ indicates spin-singlet superconductivity. The temperature dependence of the spin-lattice relaxation rate ($1\mathrm{/}{T}_1$) is convincingly described by the multigap isotropic superconducting gap. Present NMR experiments do not witness any sign of enhanced spin fluctuations in the normal state.