Stabilizing even-parity chiral superconductivity in Sr_{2}RuO_{4}

Abstract

Strontium ruthenate (Sr_{2}RuO_{4}) has long been thought to host a spin-triplet chiral p-wave superconducting state. However, the singletlike response observed in recent spin-susceptibility measurements casts serious doubts on this pairing state. Together with the evidence for broken time-reversal symmetry and a jump in the shear modulus c_{66} at the superconducting transition temperature, the available experiments point towards an even-parity chiral superconductor with k_{z}(k_{x}±ik_{y})-like E_{g} symmetry, which has consistently been dismissed based on the quasi-two-dimensional electronic structure of Sr_{2}RuO_{4}. Here, we show how the orbital degree of freedom can encode the two-component nature of the E_{g} order parameter, allowing for a local orbital-antisymmetric spin-triplet state that can be stabilized by on-site Hund's coupling. We find that this exotic E_{g} state can be energetically stable once a complete, realistic three-dimensional model is considered, within which momentum-dependent spin-orbit coupling terms are key. This state naturally gives rise to Bogoliubov Fermi surfaces.