Grimaldi, C. Max Planck Institute for the Physics of Complex Systems, Max Planck Society;
Grimaldi, C., Pietronero, L., & Strässler, S. (1995). Nonadiabatic Superconductivity: Electron-Phonon Interaction Beyond Migdal's Theorem. Physical Review Letters, 75(6), 1158-1161. doi:10.1103/PhysRevLett.75.1158.