SUPERCONDUCTIVITY IN DOPED FULLERENES - SUPERCONDUCTORS WITH WIDE-FREQUENCY-REGION PHONON-SPECTRUM

Contrary to conventional superconductors the alkali-metal-doped fuller enes have a wide-frequency-region phonon spectrum whose high- and low- frequency phonon modes are comparable to the Fermi energy E(F) and the zero-temperature gap Delta(0), respectively. This property will lead to a modification of the theory of conventional strong coupling superc onductivity. In this paper, by solving the Eliashberg equations, the e xpressions of T-c and Delta(0) are obtained. The results show that bot h the intermolecular low-frequency modes and the intramolecular high-f requency modes participate in the electron-phonon interactions; T-c ma inly arises from the high-frequency modes while Delta(0)'s enhancement mainly arises from the low-frequency modes. For this reason, the expe rimental results can be explained, especially the large ratio of 2 Del ta(0)/k(B)T(c).