  BaFe2S3 is a special iron superconductor with two-leg ladder structure which
can help to unravel the role played by the electronic correlations in high-Tc
superconductivity. At zero pressure it is insulating with stripe
antiferromagnetic (AF) order and superconductivity emerges under pressure. We
use a slave-spin technique to analyze the strength of the local correlations in
BaFe2S3. We find that at the pressure at which the superconductivity appears
the electronic correlations in BaFe2S3 are similar to the ones measured in
other iron superconductors. However, at zero pressure the strength of the
correlations is strongly enhanced, being particularly severe for the two
orbitals with the largest weight at the Fermi level what invalidates nesting as
the mechanism for AF. The system is not a Mott insulator at zero temperature,
but these two orbitals with mass enhancements m* ~ 12-15 will become incoherent
at higher temperatures. Different from what happens in other iron
superconductors, at both pressures, the Fermi surface is reconstructed by the
electronic correlations.
