Plasmon damping and response function in doped C60 compounds

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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