Interband Coulomb Interaction and Horizontal Line Nodes in Triplet Superconductor Sr$_2$RuO$_4$

TL;DR

This paper proposes that interlayer Coulomb interactions in Sr$_2$RuO$_4$ lead to horizontal line nodes in its triplet superconducting gap, offering a new mechanism for understanding its unconventional pairing symmetry.

Contribution

It introduces a novel mechanism involving interband Coulomb interactions and their second-order effects to explain horizontal line nodes in Sr$_2$RuO$_4$.

Findings

Interlayer Coulomb interactions induce $ ext{cos} rac{q_z}{2}$ dependence.

Horizontal line nodes arise from the effective interaction.

Second-order perturbation reveals the nodal structure mechanism.

Abstract

A possible mechanism for the horizontal line nodes in triplet superconductor, Sr$_2$RuO$_4$, is proposed. We consider the interlayer Coulomb interaction, as well as the on-site Coulomb repulsion, between electrons in different bands. In the second order perturbation in the interband interaction, the effective interaction becomes dependent on $\cos \frac{q_z}{2}$, resulting in the horizontal line nodes.