Spin Triplet Superconductivity in Sr2RuO4 due to Orbital and Spin Fluctuations: Analysis by Two-Dimensional Renormalization Group Theory

TL;DR

This paper demonstrates that orbital and spin fluctuations, enhanced by vertex corrections, induce triplet superconductivity in Sr2RuO4, with a specific gap structure confirmed by advanced diagrammatic calculations.

Contribution

It introduces a two-dimensional renormalization group analysis including vertex corrections to explain triplet superconductivity in Sr2RuO4.

Findings

Orbital and spin fluctuations at Q=(2π/3,2π/3) are strongly enhanced.

Triplet superconductivity with E_u symmetry is realized due to cooperative fluctuations.

The gap structure is a linear combination of sin 3kx and sin 3ky functions.

Abstract

We study the mechanism of the triplet superconductivity in Sr2RuO4 based on the multiorbital Hubbard model. The electronic states are studied using the renormalization group method. Thanks to the vertex correction (VC) for the susceptibility, which is dropped in the mean-field-level approximations, strong orbital and spin fluctuations at $Q=(2\pi/3,2\pi/3)$ emerge in the quasi one-dimensional Fermi surfaces composed of $d_{xz}$ and $d_{yz}$ orbitals. Due to the cooperation of both fluctuations, we obtain the triplet superconductivity in the $E_u$ representation, in which the superconducting gap is given by the linear combination of $(\Delta_x(k),\Delta_y(k))=(\sin 3k_x,\sin 3k_y)$. These results are confirmed by a diagrammatic calculation called the self-consistent VC method.