The electronic part (the Hopfield factor) of the electron-phonon coupling constant for alkali-metal-doped fullerenes A3C60 is calculated within the rigid muffin-tin-potential approximation. It is found that is large for tangential atomic motions, while for the radial vibrations is 20 times smaller. We have calculated for three lattice constants (a=14.1, 14.4, and 14.6) corresponding approximately to those of C60, Rb3C60, and (hypothetical) Cs3C60, and found =21, 32, and 36 eV/Ai2. Using semiempirical nearest-neighbor force constants we estimated =0.49, 0.77, and 0.83, and log=870 cm-1 for the average phonon frequency. The McMillan formula yields Tc=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 Tc on the dopant, is fully explained within the framework of the conventional superconductivity theory.
ASJC Scopus subject areas
- Condensed Matter Physics