NONADIABATIC EFFECTS IN OPTICAL PHONON SELF-ENERGY

The nonadiabatic renormalization of optical phonon frequencies and lin ewidths is studied. The phonon self-energy is calculated in the one-lo op approximation including electron-phonon interaction and impurity sc attering. The wave vector dispersion and the temperature dependence of the phonon self-energy are calculated for two model Eliashberg spectr al functions. It is shown that a strong electron-phonon interaction di minishes the nonadiabatic renormalization of a phonon frequency and sh ifts the maximum of the linewidth to the values of qv(F) higher than i t follows for Landau damping of noninteracting electrons. The vertex c orrections are studied for a system with isotropic impurity scattering . It is shown that they can give in some cases a serious qualitative c ontribution to the nonadiabatic renormalzation of phonon frequencies a nd linewidths.