Quantitative theory of superconductivity in doped C60

Abstract

The electronic part η (the Hopfield factor) of the electron-phonon coupling constant λ for alkali-metal-doped fullerenes A3C60 is calculated within the rigid muffin-tin-potential approximation. It is found that η is large for tangential atomic motions, while for the radial vibrations η is 20 times smaller. We have calculated η for three lattice constants (a=14.1, 14.4, and 14.6 Å) corresponding approximately to those of C60, Rb3C60, and (hypothetical) Cs3C60, and found η=21, 32, and 36 eV/Å2. Using semiempirical nearest-neighbor force constants we estimated λ=0.49, 0.77, and 0.83, and 〈ωlog〉=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.

Source-reported materials — not catalogue approval

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