Fermi surfaces of pure and K-doped C$_{60}$ monolayer on Cu(111) surfaces studied by high resolution angle-resolved photoemission spectroscopy

The electronic structure of C$_{60}$ on Cu(111) surfaces has been studied by high-resolution photoemission. The LEED pattern for one monolayer C$_{60}$ on a Cu(111) surface shows a sharp (4x4) pattern. In photoemission the LUMO-derived band is a partially filled by charge transfer from Cu surface and the spectrum is similar to that of gas phase C$_{60}^{-}$. The satellite peaks of LUMO indicate strong electron-phonon coupling. Comparing to spectra of K doped films the undoped 1 ML film was found to have nearly half-filled LUMO or ``K$_{3}$C$_{60}$,'' in contrast to 0.8e found in a recent calculation. [1] The Fermi surface was mapped by angle-resolved photoemission. It shows a clear electron-like pocket near the zone center, unlike the hole-like Fermi surface in ``K$_{3}$C$_{60}$'' on Ag(111), [2] due to different C$_{60}$ orientation. In the case of Cu the Fermi surface near the zone center accounts for only 0.1 electrons. Near the K-point at least one hole-like Fermi surface can be observed. The detailed Fermi surface will be discussed. [1] L.-L. Wang and H.-P. Cheng, Phys. Rev. B 69, 045404 (2004). [2] W. L. Yang et al., Science 300, 303 (2003).