Triplet $p_z$-wave pairing in quasi one dimensional A$_2$Cr$_3$As$_3$ superconductors

TL;DR

This study models the quasi-one-dimensional superconductor K$_2$Cr$_3$As$_3$ and finds that triplet $p_z$-wave pairing, driven by ferromagnetic fluctuations, is the leading pairing symmetry with line nodes on the Fermi surface.

Contribution

It introduces a minimal three-band model capturing the band structure and demonstrates triplet $p_z$-wave pairing as the dominant symmetry using RPA and mean-field analysis.

Findings

Triplet $p_z$-wave pairing is the leading symmetry.

Ferromagnetic fluctuations drive the pairing.

Line nodes exist on the $k_z=0$ plane.

Abstract

We construct minimum effective models to investigate the pairing symmetry in the newly discovered quasi-one-dimensional superconductor K$_2$Cr$_3$As$_3$. We show that a minimum three-band model based on the $d_{z^2}$, $d_{xy}$ and $d_{x^2-y^2}$ orbitals of one Cr sublattice can capture the band structures near Fermi surfaces. In both weak and strong coupling limits, the standard random phase approximation (RPA) and mean-field solutions consistently yield the triplet $p_z$-wave pairing as the leading pairing symmetry for physically realistic parameters. The triplet pairing is driven by the ferromagnetic fluctuations within the sublattice. The gap function of the pairing state possesses line gap nodes on the $k_z=0$ plane on the Fermi surfaces.