Possible altermagnetic band splitting in a Fe spin ladder system. Angle-resolved photoemission spectroscopy on BaFe2S3

We have studied the electronic structure of BaFe2S3, which is a Mott insulator with two-leg ladder structure and exhibits superconductivity under pressure, by means of angle-resolved photoemission spectroscopy. The intense spectral features with small dispersion around −0.8 and −2.0 eV are respectively attributed to Fe 3d t2g and eg bands with localized character. The weak and broad feature is observed around −0.2 eV and can be assigned to a rather itinerant eg band, which unexpectedly exhibits an energy splitting below the magnetic transition temperature. The band splitting is potentially related to altermagnetism or a novel type of ferroic order in the two-leg ladder system.