Exotic Oddness in Superconducting Sr₂RuO₄

The superconducting gap symmetry of Sr₂RuO₄ is still under debate. Most experiments suggest a triplet state, yet the best candidate order-parameter for odd-parity pairing fails to explain all experiments[1]. The most problematic issue is that the presence of nodes on the Fermi surface would rather support a d-wave symmetry[2]. A less discussed pairing function is odd-frequency Cooper pairing which may explain the intrinsic Kerr effect in this system[3]. In our study, we solve the frequency dependent Eliashberg equation[4] to investigate whether or not this pairing symmetry appears in the leading gap symmetries of Sr₂RuO₄. We used a DFT+DMFT calculation to calculate its spin excitation spectra and in turn the spin-fluctuation mediated pairing interaction. Focusing on the triplet pairing channel, we show that Sr₂RuO₄ has a stronger tendency towards odd-frequency superconductivity than towards any p-wave state.

[1] Mackenzie et al., npj Quantum Materials 2, 40 (2017)
[2] Hassinger et al., Phys. Rev. X 7, 011032 (2017)
[3] Komendová and Black-Schaffer, Phys. Rev. Lett. 119, 087001 (2017)
[4] Nourafkan et al., Phys. Rev. Lett. 117, 137001 (2016)