MODEL OF HIGHER T-C IN PHONON-MEDIATED SUPERCONDUCTORS A(3)C(60)

In alkali fullerides A(3)C(60) (A = alkali metal), a simplified BCS-li ke theory is presented in order to understand phonon-mediated supercon ductivity with a rather high transition temperature T-c. It is pointed out that the higher T-c caused by intra-molecular vibrations is relat ed with the existence of a A(+)-ion on the tetrahedral site surrounded with four nearest-neighbor C-60 molecules. The role of a A(+)-ion opt ical phonon is discussed to explain the relation between T-c and FCC-S C phase transition in ternary compounds Na(2)A'C-60 (A' = K, Rb, Cs).