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

TL;DR

This study uses $^{119}$Sn-NMR to confirm bulk multigap superconductivity in Ca$_3$Ir$_4$Sn$_{13}$, showing classic BCS signatures and spin-singlet pairing without enhanced spin fluctuations.

Contribution

First NMR evidence of multigap superconductivity in Ca$_3$Ir$_4$Sn$_{13}$, demonstrating classic BCS features and spin-singlet pairing.

Findings

Observation of Hebel-Slichter coherence peak

Exponential decay of relaxation rate below $T_c$

No signs of enhanced spin fluctuations in normal state

Abstract

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.