NMR Study of Two-Gap Superconductivity in Lu2Fe3Si5

Abstract

We report 175Lu and 29Si NMR results of the ternary-iron silicide superconductor, Lu2Fe3Si5, with \(T_{\text{c}}\sim 6.1\) K. We confirm the decrease of the Knight shift and the existence of coherence peak of nuclear spin–lattice relaxation rate, \(1/T_{1}\) of 29Si below \(T_{\text{c}}\), indicating apparently that the superconducting (SC) pairing symmetry is of the spin-singlet. The observed 175Lu-NMR signals are attributed to the Zeeman split Φ\(|{\pm} 1/2\rangle\) transition under a large nuclear quadrupole interaction. The temperature dependence of \(1/T_{1}\) of 175Lu obeys a Curie–Weiss behavior in the normal state. In the SC state, \(1/T_{1}\) decreases rapidly, and follows the \(T_{1}T=\text{const.}\) relation below \(T=1\) K, which is suggestive of the existence of the residual density of states of the conduction electrons at the Fermi level. This indicates that the small SC gap is completely suppressed even at small field of \(H\)<\(1.3\) T, and contributes to the residual Knight shift and \(1/T_{1}\) in the SC state. We speculate that the small and large SC gap are associated with the electron-like (3D-Fermi surface) and the quasi-1D hole-like pocket bands, respectively.