Electron-Phonon Vertex Corrections and Superconductivity inAlkali-Metal-Doped C₆₀ Solids

The narrow conduction band of C₆₀ leads to the breakdown of the Migdal theorem and the McMillan formula is no longer applicable. In this letter, the second-order electron-phonon vertex correction is considered to explain the superconductivity in doped C₆₀ solids and the transition temperature T_c thus obtained is in accordance with the experimental results.