Breakdown of the Migdal-Eliashberg theory in the strong-coupling adiabatic regime
Breakdown of the Migdal-Eliashberg theory in the strong-coupling adiabatic regime
In view of some recent works on the role of vertex corrections in the electron-phonon system we readress an important question of the validity of the Migdal-Eliashberg theory. Based on the solution of the Holstein model and inverse coupling constant expansion, we argue that the standard Feynman-Dyson perturbation theory by …