Superconducting state in the non-centrosymmetric Mg_{9.3}Ir_{19}B_{16.7} and Mg_{10.5}Ir_{19}B_{17.1} revealed by NMR

TL;DR

This study uses ^{11}B NMR to investigate the superconducting properties of non-centrosymmetric Mg-Ir-B compounds, revealing predominantly spin-singlet pairing with defect-induced spin-triplet components.

Contribution

It provides new insights into the pairing symmetry and the role of defects in non-centrosymmetric superconductors Mg_{9.3}Ir_{19}B_{16.7} and Mg_{10.5}Ir_{19}B_{17.1}.

Findings

Cooper pairs are mainly spin-singlet with an isotropic gap.

Defects increase spin-orbit coupling and induce spin-triplet components.

Finite spin susceptibility persists at zero temperature in more defective samples.

Abstract

We report ^{11}B NMR measurements in non-centrosymmetric superconductors Mg_{9.3}Ir_{19}B_{16.7} (T_c=5.8 K) and Mg_{10.5}Ir_{19}B_{17.1} (T_c=4.8 K). The spin lattice relaxation rate and the Knight shift indicate that the Cooper pairs are predominantly in the spin-singlet state with an isotropic gap. However, Mg_{10.5}Ir_{19}B_{17.1} is found to have more defects and the spin susceptibility remains finite even in the zero-temperature limit. We interpret this result as that the defects enhance the spin-orbit coupling and bring about more spin-triplet component.