Spin-integrated and spin-resolved photoemission study of Fe chalcogenides

The electronic structures of the antiferromagnetic semiconductor FeS and ferrimagnetic metals ${\mathrm{Fe}}_{7}{\mathrm{S}}_{8}$ and ${\mathrm{Fe}}_{7}{\mathrm{Se}}_{8}$ have been studied by spin-integrated and spin-resolved photoemission spectroscopy and inverse-photoemission spectroscopy. The overall Fe $3d$ bandwidth in the photoemission spectra is 25--30 % narrower than the density of states (DOS) predicted by first-principles band-structure calculations and is accompanied by an intense tail on the high-binding-energy side, indicating the correlated nature of electrons in the Fe $3d$ band. Deviation from the band DOS is more significant in ${\mathrm{Fe}}_{7}{\mathrm{S}}_{8}$ than in ${\mathrm{Fe}}_{7}{\mathrm{Se}}_{8}$, and in the minority-spin spectra than in the majority-spin spectra. Cluster-model calculation for FeS has shown satellite structures at high binding energies, but the calculated spectral line shape is not in good agreement with experiment compared to the band DOS. By introducing a self-energy correction to the band DOS, we could explain the narrowing of the overall Fe $3d$ bandwidth and the high-binding-energy tail shape but not for the unusual broadening of the Fe $3d$ band within $\ensuremath{\sim}1 \mathrm{eV}$ of the Fermi level.