Higher angular momentum pairing states in Sr$_2$RuO$_4$ in the presence of longer-range interactions

TL;DR

This paper investigates how longer-range interactions and spin-orbit coupling influence the pairing symmetry in Sr$_2$RuO$_4$, suggesting a $d_{x^2-y^2} + ig$ state aligns well with experiments.

Contribution

It demonstrates that including second nearest neighbor repulsions and non-local SOC stabilizes complex pairing states, advancing understanding of Sr$_2$RuO$_4$'s superconductivity.

Findings

Longer-range interactions affect pairing stability.

The $d_{x^2-y^2} + ig$ state matches experimental observations.

Non-local SOC influences pairing symmetry.

Abstract

The superconducting symmetry of Sr$_2$RuO$_4$ remains a puzzle. Time-reversal symmetry breaking $d_{x^2-y^2} + ig_{xy(x^2-y^2)}$ pairing has been proposed for reconciling multiple key experiments. However, its stability remains unclear. In this work, we theoretically study the superconducting instabilities in Sr$_2$RuO$_4$, including the effects of spin-orbit coupling (SOC), in the presence of both local and longer-range interactions within a random phase approximation. We show that the inclusion of second nearest neighbor repulsions, together with non-local SOC in the $B_{2g}$ channel or orbital-anisotropy of the non-local interactions, can have a significant impact on the stability of both $d_{x^2-y^2}$- and $g$-wave pairing channels. We analyze the properties, such as Knight shift and spontaneous edge current, of the realized $d_{x^2-y^2} + ig$, $s^{\prime}+id_{xy}$ and mixed helical pairings in different parameter spaces and find that the $d_{x^2-y^2} + ig$ solution is in better agreement with the experimental data.