SIMILARITY AND DISSIMILARITY OF DOPED FULLERENES AND OXIDE SUPERCONDUCTORS FROM THE VIEWPOINT OF ELECTRONIC-STRUCTURE

Photoemission spectroscopy shows that a very narrow peak and a broad d istribution of density-of-states coexist near the Fermi level (E(F)) i n K3C60, while the narrow peak at E(F) is not present in nonmetallic K 4C60. This shows that K4C60 is a semiconductor with an energy gap at E (F), contrary to the prediction from band structure calculations, and suggests that electron correlation is important in understanding the e lectronic structure of doped fullerenes, both metallic K3C60 and nonme tallic K4C60. The combination of photoemission, inverse photoemission and polarized oxygen-K-absorption in high T(c) oxide superconductors s hows that the hole-doping results in a similar electronic structure to that of doped fullerenes with the coexistence of a very narrow peak a nd a broad distribution of density-of-states near E(F). We discuss the similarities and differences between doped fullerenes and high-T(c) o xide superconductors based upon a comparison of their electronic struc tures.