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

Christoph M. Puetter¹ and Hae-Young Kee^1,2a

¹ Department of Physics, University of Toronto - Toronto, Ontario M5S 1A7, Canada
² Canadian Institute for Advanced Research, Quantum Materials Program - Toronto, Ontario M5G 1Z8, Canada

^a hykee@physics.utoronto.ca

Received: 17 February 2012
Accepted: 30 March 2012

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 t_2g-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 π/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.