Photoemission and inverse photoemission of alkali-doped C60

Photoemission and inverse photoemission measurements were performed on alkali-doped C60. It was found that alkali-doping in solid C60 does not cause a rigid shift of the Fermi level as in a rigid band model, but cause splitting of the LUMO band across the Fermi level, resulting in formation of an energy gap at the Fermi level at the composition of A3C60 (A;alkali metal). Strong electron correlation and lattice distortion (Jahn-Teller effect) were discussed as possible origins for the pseudo-gap. It was also found that the density of states at the Fermi level in nonsuperconducting compounds (Na-C60, Cs-C60, Rb-C70) is much smaller than those of superconducting compounds (K-C60, Rb-C60). Comparison of photoemission and inverse photoemission spectra with cuprate high-Tc superconductors were also made.