Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany

Using exact diagonalization techniques, we study a model of interacting electrons and phonons. The spectral width of the phonons is found to be reduced as the Coulomb interaction U is increased. For a system with two modes per site, we find a transfer of coupling strength from the upper to the lower mode. This transfer is reduced as U is increased. These results give a qualitative explanation of differences between Raman and photoemission estimates of the electron-phonon coupling constants for A₃C₆₀ (A=K, Rb).

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Physical Review B, 61 8628-30, 2000.