Formation of Molecular-Orbital Bands in a Twisted Hubbard Tube: Implications for Unconventional Superconductivity in K2Cr3As3

TL;DR

This paper models the molecular-orbital bands in a twisted Hubbard tube representing quasi-one-dimensional superconductors A2Cr3As3, revealing interaction-driven instabilities including spin-triplet superconductivity and spin-density waves.

Contribution

It provides an exact solution for molecular-orbital bands and derives an effective Hamiltonian showing reduced local interactions and various instabilities in a three-channel Luttinger liquid.

Findings

Identification of two spin-triplet superconducting instabilities.

Discovery of a spin-density-wave phase in certain regimes.

Reduced local interactions compared to atomic orbitals.

Abstract

We study a twisted Hubbard tube modeling the [CrAs] structure of quasi-one-dimensional superconductors A2Cr3As3 (A = K, Rb, Cs). The molecular-orbital bands emerging from the quasi-degenerate atomic orbitals are exactly solved. An effective Hamiltonian is derived for a region where three partially filled bands intersect the Fermi energy. The deduced local interactions among these active bands show a significant reduction compared to the original atomic interactions. The resulting three-channel Luttinger liquid shows various interaction-induced instabilities including two kinds of spin-triplet superconducting instabilities due to gapless spin excitations, with one of them being superseded by the spin-density-wave phase in the intermediate Hund's coupling regime. The implications of these results for the alkali chromium arsenides are discussed.