Theory for superconductivity in alkali chromium arsenides A2Cr3As3 (A=K,Rb,Cs)

TL;DR

This paper develops a theoretical model for superconductivity in alkali chromium arsenides, revealing spin triplet pairing mechanisms and different gap symmetries depending on interaction strength.

Contribution

It introduces an extended Hubbard model with molecular orbitals and analyzes pairing interactions, providing insights into the pairing symmetry and gap structure in A$_2$Cr$_3$As$_3$.

Findings

Spin triplet pairing is most attractive in certain channels.

Different pairing states emerge depending on interaction strength.

Line nodes and fully gapped states are predicted.

Abstract

We propose an extended Hubbard model with three molecular orbitals on a hexagonal lattice with $D_{3h}$ symmetry to study recently discovered superconductivity in A$_2$Cr$_3$As$_3$ (A=K,Rb,Cs). Effective pairing interactions from paramagnon fluctuations are derived within the random phase approximation, and are found to be most attractive in spin triplet channels. At small Hubbard $U$ and moderate Hund's coupling, the pairing arises from 3-dimensional (3D) $\gamma$ band and has a spatial symmetry $f_{y(3x^{2}-y^{2})}$, which gives line nodes in the gap function. At large $U$, a fully gapped $p$-wave state, $p_{z}\hat{z}$ dominates at the quasi-1D $\alpha $-band.