Identifying spin-triplet pairing in spin-orbit coupled multi-band superconductors

TL;DR

This paper explores how Hund's and spin-orbit couplings influence superconductivity in multi-orbital systems, revealing orbital-singlet spin-triplet pairing and the role of SO coupling in pairing orientation and phase relations.

Contribution

It identifies three orthogonal d-vectors for orbital-singlet spin-triplet pairing and elucidates how spin-orbit coupling affects pairing orientation and phase, advancing understanding of complex superconducting states.

Findings

Hund's interaction promotes orbital-singlet spin-triplet pairing.

Spin-orbit coupling aligns d-vectors and induces phase differences.

The theory explains features observed in Sr2RuO4 superconductivity.

Abstract

We investigate the combined effect of Hund's and spin-orbit (SO) coupling on superconductivity in multi-orbital systems. Hund's interaction leads to orbital-singlet spin-triplet superconductivity, where the Cooper pair wave function is antisymmetric under the exchange of two orbitals. We identify three d-vectors describing even-parity orbital-singlet spin-triplet pairings among t2g-orbitals, and find that the three d-vectors are mutually orthogonal to each other. SO coupling further assists pair formation, pins the orientation of the d-vector triad, and induces spin-singlet pairings with a relative phase difference of \pi/2. In the band basis the pseudospin d-vectors are aligned along the z-axis and correspond to momentum-dependent inter- and intra-band pairings. We discuss quasiparticle dispersion, magnetic response, collective modes, and experimental consequences in light of the superconductor Sr2RuO4.