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

摘要

We report bulk superconductivity (SC) in Ca$_3$Ir$_4$Sn$_{13}$ by means of$^{119}$Sn nuclear magnetic resonance (NMR) experiments. Two classicalsignatures of BCS superconductivity in spin-lattice relaxation rate ($1/T_1$),namely the Hebel-Slichter coherence peak just below the $T_c$ and theexponential decay in the superconducting phase, are evident. The noticeabledecrease of $^{119}$Sn Knight shift below $T_c$ indicates spin-singletsuperconductivity. The temperature dependence of the spin-lattice relaxationrate ($1/T_1$) is convincingly described by the multigap isotropicsuperconducting gap. Present NMR experiments do not witness any sign ofenhanced spin fluctuations in the normal state.