Spin Triplet Superconducting State due to Broken Inversion Symmetry in Li_2Pt_3B

TL;DR

This study reveals that Li_2Pt_3B exhibits spin-triplet superconductivity with line nodes, driven by broken inversion symmetry and enhanced spin-orbit coupling, contrasting with its isostructural s-wave superconductor Li_2Pd_3B.

Contribution

It demonstrates that non-centrosymmetric Li_2Pt_3B hosts a spin-triplet superconducting state, highlighting the role of spin-orbit coupling in unconventional pairing without strong electron correlations.

Findings

Spin susceptibility remains unchanged across T_c.

Spin-lattice relaxation rate follows T^3 below T_c.

Contrasts with Li_2Pd_3B, a spin-singlet superconductor.

Abstract

We report ^{11}B and ^{195}Pt NMR measurements in non-centrosymmetric superconductor Li_2Pt_3B. We find that the spin susceptibility measured by the Knight shift remains unchanged across the superconducting transition temperature T_c. With decreasing temperature (T) below T_c, the spin-lattice relaxation rate 1/T_1 decreases with no coherence peak and is in proportion to T^3. These results indicate that the Cooper pair is in the spin-triplet state and that there exist line nodes in the superconducting gap function. They are in sharp contrast with those in the isostructural Li_2Pd_3B which is a spin-singlet, s-wave superconductor, and are ascribed to the enhanced spin-orbit coupling due to the lack of spatial inversion symmetry. Our finding points to a new paradigm where exotic superconductivity arises in the absence of strong electron-electron correlations.