*
A.I. Liechtenstein (a), O.Gunnarsson (a), M. Knupfer (b), J. Fink (b) and J.F. Armbruster (c)
(a) Max-Planck-Institut für Festkörperforschung, Stuttgart
(b) Institut für Festkörperforschung, IFW Dresden, Dresden
(c) Forschungszentrum Karlsruhe, Institut für Nukleare Festkörperphysik, Karlsruhe
*

We present experimental and theoretical results for the broadening of the 0.5 eV charge carrier plasmon in A3C60 (A=K, Rb) compounds. The experimental width (0.5 eV) is very large and comparable to the plasmon energy. We have performed RPA calculations for a three-band model of orientationally disordered C60 molecules. We show that it is unlikely that the width can be caused by the disorder or by a decay in single electron-hole pair excitations. Instead we have studied the decay in an electron-hole pair dressed by phonon excitations. We have calculated the response function, using Green's functions dressed by the self-energy due to the electron-phonon interaction. Vertex corrections are 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 with experiment.

J. Phys.: Condens. Matter **8**, 4001 (1996).

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