LOWER CRITICAL FIELDS OF ALKALI-METAL-DOPED FULLERENE SUPERCONDUCTORS

We report on the lower critical field of fullerene superconductors der ived from a ''trapped magnetic moment'' method. Superconducting K3C60, Rb3C60, and RbCs2C60 crystals and powders with shielding fractions be tween 3 and 100 % were investigated. In contrast to all previous inves tigations made by other methods, the values of H-c1 are much smaller a nd of the order of 1 mT at T=0. We show that the smallness of H-c1 is not related to Josephson junctions and granularity, but is an intrinsi c property of the fullerenes.