Raman scattering and electron phonon coupling in A3C60

Raman scattering measurements performed in situ in UHV on thin and ultrathin films of doped C60 are reported for variations in alkali-metal type, composition and temperature. The results emphasize the important role of disorder on Raman processes and the probing of electron-phonon coupling relevant to superconductivity. Detailed comparisons of free carrier phonon damping effects on selected radial and tangential intramolecular phonons are discussed in Rb3C60 and K3C60 using nonmetallic Na3C60 as a reference. Elevated temperature studies of Na3C60 suggest a transition to a more metallic state. Intermolecular Raman scattering associated with alkali-metal motion, weakly coupled to C60 clusters is reported. The effects of alkali size, lattice thermal expansion and disorder are discussed.