Superconductivity in expanded fcc C-60(3-) fullerides

The behavior of A(2)C(60) superconductors at the large inter-fulleride sepa ration where the transition temperatures (T-c) are highest is investigated by the synthesis and structural and electronic characterization of face-cen tered cubic (fcc) A(3)C(60) compounds with the largest lattice parameters y et found. In this family T-c decreases with increasing inter-fulleride sepa ration, despite a continued increase in the density of states at the Fermi level. This contrasts with T-c(a) relationships previously demonstrated for these materials and is consistent with recent suggestions that the interel ectron repulsions between carriers in the t(1u) band are important in deter mining T-c in a fulleride metal near the Mott-Hubbard transition.