ELECTRONIC STATES AND SUPERCONDUCTIVITY IN ALKALI-INTERCALATED FULLERIDES - C-13-NMR STUDY IN NA2RBC60, NA2CSC60, K3C60, K2RBC60, K2CSC60, KRBCSC60, RB2CSC60 AND RBCS2C60
Y. Maniwa et al., ELECTRONIC STATES AND SUPERCONDUCTIVITY IN ALKALI-INTERCALATED FULLERIDES - C-13-NMR STUDY IN NA2RBC60, NA2CSC60, K3C60, K2RBC60, K2CSC60, KRBCSC60, RB2CSC60 AND RBCS2C60, Journal of the Physical Society of Japan, 63(3), 1994, pp. 1139-1148
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.