Superconducting Symmetries of Sr₂RuO₄ from Spin- and Charge-fluctuations

Although the normal state of Sr₂RuO₄ is well understood, its pairing symmetry is still debated [1]. From its correlated multi-orbital normal state, we construct the spin- and charge-fluctuation pairing interactions. These interactions depend on the proximity to an instability and on the size of the screened Hund's coupling. We present the leading gap function symmetries obtained by solving the frequency dependent linearized Eliashberg equation [2]. Close to magnetic instabilities, we find spin-singlet d-wave pairing. Away, where charge-fluctuations increase, we observe the emergence of two even-parity spin-triplet states: an odd in frequency s-wave and two degenerate momentum-independent states that pair electrons on different orbitals and are odd in orbial indices. We will explain by what means spin- and charge-fluctuations mediated pairing favors such symmetries, how to understand them from specific features of the correlated electronic structure and compare their gap value with experiments.

[1] Mackenzie et al., npj Quantum Materials 2, 40 (2017)
[2] Gingras et al., arXiv:1808.02527 [cond-mat] (2018)