Electron-phonon coupling and superconductivity in alkali-intercalatedC60solid
We propose that superconductivity in ${\mathit{A}}_{3}$${\mathrm{C}}_{60}$ (A=K, Rb) with ${\mathit{T}}_{\mathit{c}}$\ensuremath{\ge}30 K results from a favorable combination of high phonon frequencies and the existence of two different energy scales optimizing the coupling constant \ensuremath{\lambda}=NV. Calculations show that electron scattering V is dominated by particular on-ball Jahn-Teller-type modes on the scale of the large on-ball \ensuremath{\pi}-hopping energy, while the density of states N is controlled by the weak interball hopping energy. This factorization has several observed experimental consequences. Crucial differences to intercalated graphite explain the much smaller ${\mathit{T}}_{\mathit{c}}$ values in the graphite compounds.