Formation of Molecular-Orbital Bands in a Twisted Hubbard Tube: Implications for Unconventional Superconductivity inK2Cr3As3

Abstract

We study a twisted Hubbard tube modeling the $[\mathrm{CrAs}{]}_{\infty }$ structure of quasi-one-dimensional superconductors $A_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ ($A=\mathrm{K}$, 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two kinds of spin-triplet superconducting instabilities due to gapless spin excitations, with one of them being superseded by the spin-density-wave phase in the intermediate Hund’s coupling regime.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.