Motivated by the recent discovery of superconductivity in the iron-based ladder compound BaFe2S3 under high pressure, we derive low-energy effective Hamiltonians from first principles. We show that the complex band structure around the Fermi level is represented only by the Fe 3dxz (mixed with 3dxy) and 3dx2−y2 orbitals. The characteristic band degeneracy allows us to construct a four-band model with the band unfolding approach. We also estimate the interaction parameters and show that the system is more correlated than the 1111 family of iron-based superconductors. Provided the superconductivity is mediated by spin fluctuations, the 3dxz-like band plays an essential role, and the gap function changes its sign between the Fermi surface around the Γ point and that around the Brillouin-zone boundary.
@article{arxiv.1507.05715,
title = {Ab initio downfolding study of the iron-based ladder superconductor BaFe$_2$S$_3$},
author = {Ryotaro Arita and Hiroaki Ikeda and Shiro Sakai and Michi-To Suzuki},
journal= {arXiv preprint arXiv:1507.05715},
year = {2015}
}