Resonant photoemission study of pyrite-type, and

The electronic structure of pyrite-type (Formula presented), (Formula presented), and (Formula presented) has been studied by photoemission spectroscopy. From resonant photoemission studies and configuration-interaction cluster-model analysis of the spectra, (Formula presented) is found to be a charge-transfer-type insulator, the band gap of which is formed between the occupied S 3p and the empty Ni 3d states. Cluster-model calculations indicate that the short Fe-S distance favors the low-spin (S=0) ground state in (Formula presented) compared to the high-spin FeS. Resonant photoemission results indicate a sign of electron correlation in the nonmagnetic semiconductor (Formula presented).