RAMAN STUDIES OF ELECTRON-PHONON INTERACTION IN KXC70

The Raman spectra of pristine C70 films and KxC70 doped to the maximum-conductivity phase (nominally K4C70) are studied. All the Raman modes for C70 are only moderately broadened upon K doping, distinctively different from the superconducting K3C60 where several H(g) modes are broadened to the extent that they have almost disappeared from the spectrum. Assuming that the electron-phonon interaction is responsible for the broadening, the electron-phonon coupling strength is found to be comparable to the Coulomb repulsion. These results are important for understanding the absence of superconductivity in KxC70.