A study was made of the role played by alkali-metal vacancies in the structure and superconductivity of Rb3C60. This was done by preparing samples with various alkali-metal loadings and annealing temperatures, in order to identify a possible role of non-stoichiometry in superconductivity. Sample-to-sample variations of about 1K were found in the superconducting transition temperature, but this did not correlate with the vacancy concentration. It was concluded that a model of the electronic structure of alkali-metal fullerenes, based upon proximity to a Mott-Hubbard transition at integer doping, was not applicable.

Transition Temperatures and Vacancies in Superconducting Rb3C60. A.Huq, P.W.Stephens: Physical Review B, 2005, 72[9], 092511 (3pp)