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Many seemingly contradictory experimental findings concerning the superconducting state in Sr2RuO4 can be accounted for on the basis of a conjectured accidental degeneracy between two patterns of pairing that are unrelated to each other under the (D4h) symmetry of the crystal: a dx2-y2-wave (B1g) and a gxy(x2-y2)-wave (A2g) superconducting state. In this paper, we propose a generic multiband model in which the g-wave pairing involving the xz and yz orbitals arises from second-nearest-neighbor BCS channel effective interactions. Even if timereversal symmetry is broken in a d + ig state, such a superconductor remains gapless with a Bogoliubov Fermi surface that approximates a (vertical) line node. The model gives rise to a strain-dependent splitting between the critical temperature Tc and the time-reversal symmetry-breaking temperature TTRSB that is qualitatively similar to some of the experimental observations in Sr2RuO4. 

Abstract A variety of precise experiments have been carried out to establish the character of the superconducting state in Sr 2 RuO 4 . Many of these appear to imply contradictory conclusions concerning the symmetries of this state. Here we propose that these results can be reconciled if we assume that there is a near-degeneracy between a $${d}_{{x}^{2}-{y}^{2}}$$ d x 2 − y 2 (B 1 g in group theory nomenclature) and a $${g}_{xy({x}^{2}-{y}^{2})}$$ g x y ( x 2 − y 2 ) (A 2 g ) superconducting state. From a weak-coupling perspective, such an accidental degeneracy can occur at a point at which a balance between the on-site and nearest-neighbor repulsions triggers a d -wave to g -wave transition.