Browsing by Author "Rösch, Oliver"

Now showing 1 - 1 of 1

Open Access
Electron phonon interaction in strongly correlated materials
(2005) Rösch, Oliver; Andersen, Ole Krogh (Prof. Dr.)
We study electron-phonon interaction in strongly correlated systems where the interplay with electron-electron interactions needs to be taken into account explicitly. We specifically consider cuprate high-temperature superconductors but also investigate in more general terms the influence of strong correlations. We first develop a model framework by deriving an effective low-energy model from a three-band model of the copper oxide planes in the cuprates allowing for the modulation of its parameters by lattice distortions. The electron-phonon interaction in the resulting t-J model with phonons is dominated by the on-site coupling due to phonon-induced changes in the large energy gain of Zhang-Rice singlets. Using exact diagonalization of finite clusters, we find that this model successfully describes the anomalous softening upon doping of the oxygen half-breathing mode in these compounds. Both the dependence on doping and the phonon wavevector are in good agreement with experiment. A comparison with results from a Hartree-Fock mean-field approximation of the three-band model shows the importance of treating strong correlations directly. After deriving the additional electron-phonon interaction that arises in undoped cuprates from the modulation of the electrostatic potential, we conclude that the coupling is strong enough to lead to the polaronic behavior seen in photoemission from these systems. Based on an adiabatic approximation, we explain the dispersion of the phonon side band according to predictions from purely electronic models and develop an efficient method for calculating spectra. Applying it to our model yields results that agree well with experiment. Finally, we use sum rules for the phonon and the electron self-energy to show generally that due to strong correlations the effect of electron-phonon interaction can be at variance from what is expected for non-interacting electrons. Electronic and phononic properties are affected differently leading to a mismatch of the respective apparent electron-phonon couplings. We also discuss the importance of vertex corrections to the electron-phonon interaction in strongly correlated materials.