ELECTRONIC STATES AND SUPERCONDUCTIVITY IN ALKALI-INTERCALATED FULLERIDES - C-13-NMR STUDY IN NA2RBC60, NA2CSC60, K3C60, K2RBC60, K2CSC60, KRBCSC60, RB2CSC60 AND RBCS2C60

A systematic C-13 NMR experiment is reported in alkali-fullerides A3C6 0 (where A3 is alkali-metals) between superconducting transition tempe rature T(c) and approximately 100 K. Careful C-13 NMR spin-lattice rel axation time study clarified the properties of the conduction electron wave functions at Fermi surface. An upper limit of Stoner exchange pa rameter was estimated to be approximately 3 eV/(spin-carbon), which is far from spin-wave instability criterion. Based on these studies, a v ariation of the density of states at Fermi level, N(E(f)), with T(c) w as deduced. The results were analyzed in terms of McMillan formula, le ading to weak or medium electron-phonon coupling constants and relevan t phonon energy larger than 600 K. It was strongly suggested that the A3C60 superconductor is described within a framework of the convention al phonon-mediated BCS superconductivity.