Superconducting Symmetries of Sr$_2$RuO$_4$ from First-Principles Electronic Structure

Abstract

Although correlated electronic-structure calculations explain very well the normal state of Sr$_2$RuO$_4$, its superconducting symmetry is still unknown. Here we construct the spin and charge fluctuation pairing interactions based on its correlated normal state. Correlations significantly reduce ferromagnetic in favor of antiferromagnetic fluctuations and increase inter-orbital pairing. From the normal-state Eliashberg equations, we find spin-singlet $d$-wave pairing close to magnetic instabilities. Away from these instabilities, where charge fluctuations increase, we find two time-reversal symmetry-breaking spin-triplets: an odd-frequency $s$-wave, and a doubly-degenerate inter-orbital pairing between $d_{xy}$ and ($d_{yz},d_{xz}$).