Comparative photoemission study of RbxC60, RbxC70 and RbC8

A comparative photoemission study on RbxC60, RbxC70 and RbC8 (graphite intercalation compound) is reported. It was found that the Fermi level of Rb3C60 is located at the bottom of a valley of the density of states, while that of RbC8 is at a maximum point of the occupied states. This experimental result is explained in terms of the existence of a pseudo-gap at the Fermi level in the fulleride. This indicates that a rigid-band picture is not a good starting point for understanding the change of the electronic structure upon the alkaline-doping. It was also found that the density of states at the Fermi level is much smaller in RbxC70 than in RbxC60. This accounts for the less conductive nature and the absence of superconductivity in RbxC70.