Valence-band photoemission study of R₃S₄ (R=La, Ce)

Electronic structures of R₃S₄ (R=La, Ce) has been investigated by using photoemission spectroscopy (PES) and electronic structure calculations performed in the LSDA and the LSDA+U method. The valence-band spectrum of La₃S₄ reveals that the electronic states near E_F have mainly La 5d character, in agreement with the LSDA calculation. The Ce 4f PES spectrum exhibits three prominent features at about -0.5 eV, -2.5 eV, and -5.5 eV. We interpret the Ce 4f spectrum as the essentially trivalent Ce 4f spectrum, and identify the peaks at -0.5 eV and -2.5 eV as the correlation-split 4f states, and the -5.5 eV peak as the hybridized 4f/5d states with S p electrons. The CIS and CFS yield spectra show that Ce₃S₄ has formally trivalent Ce³⁺ ions. Nearly half-metallic nature is obtained for ferromagnetic Ce₃S₄, and the LSDA+U calculation provides a reasonably good description of the electronic structure of Ce₃S₄. Superconductivity in La₃S₄ and the absence of the tetragonal distortion in Ce₃S₄ have been discussed based on their electronic structures.