On Possible Coexistence of Superconductivity and Charge Density Wave in Hole Doped C$_{60}$

Abstract

We study metallic behavior and superconductivity in C$_{60}$ materials in terms of a tight binding model characterized by an intramolecular, nonretarded attraction. It was shown previously that, at intermediate coupling, the model possesees a state in which s-wave superconductivity coexists with a charge density wave, the latter stabilized by intersite repulsion. The CDW causes $T_c$ to decrease near half filling. We examine the conditions under which such a state may exist in C$_{60}$. The key issue is the role of metallic screening which is treated in a parameter-free fashion. We show that screening is strong enough to stabilize a conventional (i.e., without a CDW) state in electron-doped C$_{60}$ and A$_3$C$_{60}$. But in hole-doped C$_{60}$, for which $T_c$ peaks away from half filling, a CDW-superconductor can not be ruled out. We discuss some normal state anomalies for such a state.