Raman scattering in calcium-doped C-60

Experimental results on Raman-scattering spectra of CaxC60 (x=3,5) taken at room temperature are presented and discussed. The high-frequency lines associated with the tangential vibrational modes are observed to down-shift relative to their position in C-60, which is similar to that of alkali-metal-doped C-60 In contrast, the low-frequency line of the radial Ag mode strongly shifts to higher frequencies with increasing calcium concentrations. This upshift is much larger than that of alkali-doped C-60 for the same charge transfer. This behavior indicates that the radial Ag mode is strongly dependent on the doping metal and that there exists a strong interaction between the C-60 molecule and the surrounding metal ions. In superconducting Ca5C60, a strong damping of Hg(7) and Hg(8) modes is observed due to substantial electron-phonon coupling.