Singlet-triplet mixed state in spin-orbital-parity coupled superconductors

TL;DR

This paper investigates how spin-orbit-parity coupling in centrosymmetric superconductors induces mixing of singlet and triplet pairings, explaining high critical fields and proposing experimental detection methods.

Contribution

It reveals the strong singlet-triplet pairing mixing caused by spin-orbit-parity coupling near topological band inversion in centrosymmetric superconductors.

Findings

Enhanced in-plane critical fields beyond Pauli limit.

Anisotropic critical field behavior explained by pairing mixing.

Proposed measurement of Andreev reflection to detect triplet pairing.

Abstract

Unlike noncentrosymmetric superconductors, the effects of spin singlet- and spin triplet-pairing mixing in centrosymmetric superconductors remain ambiguous. Recently, it was experimentally demonstrated that an anisotropically enhanced in-plane critical fields beyond Pauli limit would be induced by the coupling of spin,orbit and parity ($p$-, $d$-orbitals) degrees of freedom in centrosymmetric transition metal dichacogenides , which is called as spin-orbit-parity coupled (SOPC) superconductors. In this work, we show that the SOPC would induce a strong spin-singlet and spin-triplet pairing mixing near the topological band inversion in this system. Moreover, we find that the presence of such mixing provides a close explanation of the observed the in-plane upper critical fields $B_{c2}$ in terms of both the enhancement and anisotropy. We also propose measuring the equal-spin Andreev reflection between 2M-WS$_2$ and a ferromagnetic (FM) lead to detect the spin-triplet pairing in 2M-WS$_2$. Our work paves a way to study the spin-singlet and spin-triplet pairing in centrosymmetric superconductors with strong spin-orbital parity coupling.