Inelastic neutron scattering results on Rb3C60 and Rb6C60

Abstract Using inelastic neutron scattering we have obtained the generalized phonon density-of-states PDOS G( hω ) for the superconducting fullerite Rb 3 C 60 and the insulating fullerite Rb 6 C 60 in the energy region from 2 meV to 12 meV and for various temperatures between 10 K and 300 K. The PDOS of Rb 3 C 60 in the range from 4 meV to 7 meV is strongly temperature dependent between 78 K and 300 K. In addition, a weak anomalous softening of excitations in the range from 2 meV to 4 meV is observed for temperatures below 78 K. The PDOS of Rb 6 C 60 is significantly different from the one for Rb 3 C 60 and no significant temperature dependences are observed.