ELECTRONIC-STRUCTURE OF EU AND YB GRAPHITE-INTERCALATION COMPOUNDS

An angle-resolved photoemission (PE) study is performed on graphite in tercalation compounds (GIC's) with Eu and Yb prepared in situ by depos ition of the pure metals onto single-crystalline graphite (0001) surfa ces and subsequent annealing. The low-energy-electron-diffraction patt erns reveal a sharp (root 3 x root 3)R30 degrees overstructure as obse rved for other rare-earth (RE) and alkali GIC's. The PE data are in ex cellent agreement with local-density-approximation band-structure calc ulations for stage-2 GIC's that indicate charge transfer of about 0.5 electrons per RE atom into graphite-derived states of pi symmetry. Thi s charge transfer is caused by an energetical lowering of the graphite -derived pi bands and leads to the appearance of an intense Fermi-leve l structure in the PE spectra taken around the K(Gamma') point of the Brillouin zone. Admixtures of rare-earth-derived d states are found cl ose to the Fermi energy in the region of the Gamma and the M' points.