QUANTITATIVE THEORY OF SUPERCONDUCTIVITY IN DOPED C-60

The electronic part eta-(the Hopfield factor) of the electron-phonon coupling constant-lambda for alkalimetal-doped fullerenes A3C60 is calculated within the rigid muffin-tin-potential approximation. It is found that eta is large for tangential atomic motions, while for the radial vibrations-eta is 20 times smaller. We have calculated-eta for three lattice constants (a = 14.1, 14.4, and 14.6 angstrom), corresponding approximately to those of C60, Rb3C60, and (hypothetical) Cs3C60, and found eta = 21, 32, and 36 eV/angstrom2. Using semiempirical nearest-neighbor force constants we estimated lambda = 0.49, 0.77, and 0.83, and <omega(log)> = 870 cm-1 for the average phonon frequency. The McMillan formula yields T(c) = 5, 36, and 44 K for these lattice constants, in reasonable agreement with the available experimental data. The relatively high-temperature superconductivity in A3C60, as well as the strong dependence of T(c) on the dopant, is fully explained within the framework of the conventional superconductivity theory.