The role of spin-orbit coupling for the superconducting state in Sr ₂ RuO ₄

The odd-parity spin-triplet Cooper pairing states show a six-fold degeneracy for a quasi–two-dimensional electron system. In this article we show how spin-orbit coupling can lift this degeneracy for Sr 2 RuO 4 taking the band structure based on the three relevant t 2 g -orbitals of the Ru-ions into account. The stabilized state depends on the relative strength of the pairing interaction. We show that under reasonable assumptions the chiral pairing state d ( k ) = ẑ ( k x ± ik y ) is favored against the others.