One-electron spectrum in strongly coupled electron-phonon system

Using the perturbation expansion for the one-electron Green function a new selfconsistent method for the determination of parameters f lambda , denoting the lattice distortions around an excess electron is introduced. It is shown that f lambda depends mainly on the quotient between the polaron group velocity and the phonon phase velocity, and on the damping Gamma of the polaron states. From polaron eigenstates and their Gamma , the one-electron spectrum is calculated for the adiabatic and the nonadiabatic case. Abrupt temperature-dependent changes in the spectrum are not observed.