We show that the interplay between spin and charge fluctuations in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ leads unequivocally to triplet pairing which has a hidden quasi-one-dimensional character. The resulting superconducting state spontaneously breaks time-reversal symmetry and is of the form $\Delta \sim (p_x+i{p}_y)\widehat{z}$ with sharp gap minima and a $d$ vector that is only weakly pinned. The superconductor lacks robust chiral Majorana fermion modes along the boundary. The absence of topologically protected edge modes could explain the surprising absence of experimentally detectable edge currents in this system.

• Received 26 March 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.136401