$^{119}$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 ($1/T_1$), 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 ($1/T_1$) 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. 
R. Sarkar, F. Br\"uckner, M. G\"unther, C. Petrovic, Kefeng Wang, P.   K. Biswas, H. Luetkens, E. Morenzoni, A. Amato, and H...
cond-mat.supr-con