Non-unitary triplet pairing in the centrosymmetric superconductor LaNiGa$_2$

TL;DR

This study reveals that LaNiGa$_2$ is a centrosymmetric superconductor exhibiting non-unitary triplet pairing and breaking time reversal symmetry, indicating a new family of paramagnetic non-unitary superconductors.

Contribution

It demonstrates the presence of non-unitary triplet pairing in a centrosymmetric superconductor, expanding understanding of unconventional superconductivity.

Findings

Spontaneous magnetic fields appear at superconducting transition.

Superconducting state breaks time reversal symmetry.

LaNiGa$_2$ is analogous to LaNiC$_2$ in pairing symmetry.

Abstract

Muon spin rotation and relaxation experiments on the centrosymmetric intermetallic superconductor LaNiGa$_2$ are reported. The appearance of spontaneous magnetic fields coincides with the onset of superconductivity, implying that the superconducting state breaks time reversal symmetry, similarly to non-centrosymmetric LaNiC$_2$. Only four triplet states are compatible with this observation, all of which are non-unitary triplets. This suggests that LaNiGa$_2$ is the centrosymmetric analogue of LaNiC$_2$. We argue that these materials are representatives of a new family of paramagnetic non-unitary superconductors.