Strong interplay between electron-phonon interaction and disorder in low doped systems.

The effects of doping on the spectral properties of low-doped systems are investigated by means of the coherent potential approximation to describe the distributed disorder induced by the impurities and the phonon-phonon noncrossing approximation to characterize a wide class of electron-phonon interactions that dominate the low- energy spectral features. When disorder and electron-phonon interaction work on comparable energy scales, a strong interplay between them arises, the effect of disorder can no longer be described as a mere broadening of the spectral features, and the phonon signatures are still visible despite the presence of strong disorder. As a consequence, the disorder-induced metal-insulator transition is strongly affected by a weak or moderate electron-phonon coupling, which is found to stabilize the insulating phase.