Electron-phonon coupling strength and implications for superconductivity in alkali-metal-doped fullerenes

Abstract

A comparison between the electron-phonon coupling strength in graphite intercalation compounds and alkali-metal-doped ${\mathrm{C}}_{60}$ is considered. It is shown that the curvature of ${\mathrm{C}}_{60}$ leads to a slight reduction in the modulation of the single-site matrix element in comparison with the corresponding value in graphite. Nevertheless, the curvature of ${\mathrm{C}}_{60}$ makes it possible for electrons to couple with the low-frequency radial modes. This coupling causes the value of the dimensionless electron-phonon coupling parameter, λ, to be reasonably large. The large value of λ together with a large value of the density of states at the Fermi level, in turn, readily yields a transition temperature of the order of 30 K for alkali-metal-doped ${\mathrm{C}}_{60}$ compounds.