Screening, Coulomb Pseudopotential, and Superconductivity in Alkali-Doped Fullerenes

We study the static screening in a Hubbard-like model using quantum Monte Carlo methods. We find that the random phase approximation is surprisingly accurate almost up to the Mott transition. We argue that in alkali-doped fullerenes the Coulomb pseudopotential μ* is not very much reduced by retardation effects. Therefore efficient screening is important in reducing μ* sufficiently to allow for an electron-phonon driven superconductivity. In this way the fullerides differ from the conventional picture, where retardation effects play a major role in reducing the electron-electron repulsion.