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

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) ${\hat{I}}^3$ 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 $\hat{I}\pm$-band.