Effect of S 3p and Se 4p holes on charge fluctuations in pyrite-type CuS₂ and CuSe₂ revealed by hard x-ray photoemission spectroscopy

Bulk electronic states of pyrite-type CuS2 and CuSe2 have been investigated by means of hard x-ray photoemission spectroscopy (HAXPES). In the valence-band HAXPES spectra, the Cu 3d subshell is basically fully occupied in CuS2 and CuSe2, and the partially occupied anion p orbitals are responsible for the metallic behavior. This situation is opposite to the various conducting transition-metal compounds with open shell transition-metal cations and closed shell anions. The Cu 2p core-level HAXPES spectra exhibit satellite peaks, which indicate the presence of charge fluctuations mediated by inverse charge transfer from Cu 3d to S 3p/Se 4p. © 2025 American Physical Society.