Angle-resolved ultraviolet photoemission study of first stage alkali-metal graphite intercalation compounds

The electronic band structure of the first stage alkali-metal graphite intercalation compounds (C₈K, C₈Rb and C₈Cs) was determined by angle-resolved ultraviolet photoelectron spectroscopy. The dispersive feature of the π^* bands at {Mathematical expression} point in the Brillouin zone was clearly observed in all the compounds. The electron occupancies in the π^* band of C₈K, C₈Rb and C₈Cs were estimated to be 0.5±0.05 e (e; unit electronic charge), 0.45±0.05 e and 0.4±0.05 e, respectively. This strongly suggests that another half of the unit electronic charge is accommodated in the three-dimensional band at Γ point, which forms a spherical Fermi surface at the center of the Brillouin zone. The character of the three-dimensional band at Γ point was also discussed.