Surface electronic structure of epitaxial Ce and La films

We report on a detailed photoemission (PE) study of monocrystalline Ce and La metal films grown on W(110). Angle-resolved PE reveals that both systems have very similar valence-band structures, with the observed dispersions being in good agreement with local-density approximation band-structure calculations. These calculations were performed for three different close-packed crystal structures of La and Ce metal, giving evidence for a double hcp structure of the films, i.e., a β phase in the case of Ce. The pronounced surface state, characteristic for the close-packed surfaces of trivalent lanthanide metals, is shown to exist also for β-Ce(0001), extending over a wide range of the surface Brillouin zone. The 4f electronic structure of the Ce film was studied by resonant PE at the 4→d4f threshold. A separation of bulk and surface contributions with high resolution was achieved by quenching the surface signal with a Dy overlayer. In this way, a surface shift of (140±40) meV of the 4f⁰ final state emission was found for β-Ce, which is discussed in connection with f-d hybridization.