THE synthesis of macroscopic quantities1,2 of the fullerenes C60 and C70 has led to discoveries of several unusual properties3-10, in particular the high conductivity3 and superconductivity4-6 of alkali-metal-doped phases. Here we report a superconducting phase of C60 doped with caesium and rubidium, which has the highest transition temperature Tc and the largest diamagnetic shielding found so far for the alkali-metal-doped compounds. CSxRbyC60 (x = 2 and y = 1 in the dopant feed) exhibits a Tc of 33 K and a diamagnetic shielding of over 60%. This is also the highest Tc yet observed in a molecular superconductor. The vari-ation of Tc with dopant, Tc (KxC60) [18 K]< Tc (RbxC60) [∼29 K]< Tc (CsxRbyC60) [33 K], supports the interpretation that the transi-tion temperature of these fullerides is determined mainly by the density of states at the Fermi level.
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