Renormalization group analysis for the quasi-one-dimensional superconductor BaFe2 S3

Motivated by the discovery of superconductivity in the two-leg, quasi-one-dimensional ladder compound BaFe2S3, we present a renormalization group study of electrons moving on a two-leg, two-orbital ladder, subjected to Hubbard repulsion U and Hund's coupling J. In our calculations, we adopt tight-binding parameters obtained from ab initio studies on this material. At incommensurate filling, the long-wavelength analysis displays four phases as a function of 0≤J/U<1. We show that a fully gapped superconductor is stabilized at sufficiently large Hund's coupling, the relative phases at the three Fermi points are "+,-,-". By contrast, when the system is tuned to half-filling, umklapp scattering gives rise to Mott insulating phases. We discuss the general implications of our study for the broad class of iron-based superconductors.