Abstract
The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3
[H. Takahashi et al., Nat. Mater. 14, 1008 (2015)] opens a broad avenue of research, because it represents the
first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor.
Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body
techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In
this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders
of BaFe2S3. The model is studied with the density matrix renormalization group. These first reported results are
exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the
rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments;
and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of
two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with
doping, with only oneWannier orbital receiving the hole carriers while the other remains half-filled. These results
suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies
and other exotic properties of iron-based high-critical-temperature superconductors in general.
