PLASMON DAMPING AND RESPONSE FUNCTION IN DOPED C-60 COMPOUNDS

We present experimental and theoretical results for the broadening of the 0.5 eV charge carrier plasmon in A(3)C(60) (A=K, Rb) compounds. Th e experimental width (0.5 eV) is very large and comparable to the plas mon energy. We have performed RPA calculations for a three-band model of orientationally disordered C-60, molecules. We show that it is unli kely that the width can be caused by the disorder or by a decay in sin gle electron-hole pair excitations. Instead we have studied the decay in an electron-hole pair dressed by phonon excitations. We have calcul ated the response function, using Green's functions dressed by the sel f-energy due to the electron-phonon interaction. Vertex corrections ar e included to satisfy the Ward identity. We show that this leads to a width of the plasmon which is comparable to its energy, in agreement w ith experiment.