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In 2015 superconductivity with Tc~24 K was discovered in BaFe₂S₃ [1]. Superconductivity appears under pressure, when a stripe antiferromagnetic phase is suppressed. Contrary to what happens in other 2D materials BaFe₂S₃ is not a layered material but it contains quasi-one dimensional Fe₂S₃ ladders and the antiferromagnetic state is insulating. BaFe₂S₃ has been claimed to be a Mott insulator. By using slave-spin methods we have analyzed the correlation strength of BaFe₂S_3. We find that at zero pressure BaFe₂S₃ is very strongly correlated. Some of the orbitals can be considered to be localized while others remain metallic. At pressures at which the superconductivity appears the correlations have been reduced to values similar to those in iron superconductors, close to the Hund metal crossover, but still shows important orbital differentiation. Our work emphasizes the role of intermediate correlations in the appearance of high-Tc superconductivity.
[1] H.Takahashi et al, Nat. Mat. 14, 1008 (2015)