DOPANT ISOTOPE EFFECT ON SUPERCONDUCTIVITY IN RB3C60

In order to distinguish between the role of intra- and inter-molecular phonons in the mechanism of C60 superconductors, the dopant isotope effect has been studied for the Rb3C60 superconductor using three different samples: Rb-85, Rb-87 and natural Rb isotopic composition. Unlike the carbon isotope effect, changing the mass of the Rb dopant does not change the superconductive onset temperature T(c) of the material beyond experimental error. From these results it is concluded that the active phonons in the superconductivity are of intra-molecular and not of inter-molecular nature.