Shadowed Triplet Pairings in Hund's Metals with Spin-Orbit Coupling

Hund’s coupling in multi-orbital systems allows for the possibility of even-parity orbital-antisymmetric spin-triplet pairing which can be stabilized by spin-orbit coupling (SOC). This pairing appears at the Fermi surface (FS) as a pseudospin-singlet, with the momentum-dependence determined by the SOC and the underlying triplet character remaining in the form of interband pairing away from the FS. Here, we examine the role of momentum-dependent SOC (k-SOC) in generating non-trivial pairing symmetries at the FS, and the hidden triplet nature associated with this inter-orbital pairing, which we dub a “shadowed triplet”. Applying this concept to Sr₂RuO₄, we first derive several forms of k-SOC with d-wave form-factors from a microscopic model and subsequently show that for a reasonable range of SOC parameters, a pairing state with s + id_xy symmetry at the FS can be stabilized. This pairing state is distinct from pure spin-singlet and -triplet pairings due to its unique character of pseudospin-singlet pairing on the FS with underlying pseudospin-triplet nature away from the FS. We discuss experimental probes to differentiate the shadowed triplet pairing from conventional pseudospin-triplet and -singlet pairings.

[1] J. Clepkens, A. W. Lindquist, and H.-Y. Kee, arXiv:2009.08597