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We study electron-phonon interaction in strongly correlated materials like the cuprate superconductors. Using sum rules, we show that its effect on phonon properties is strongly suppressed at low doping, while there is no corresponding reduction for the electron self-energy. This can lead to discrepancies between apparent coupling constants calculated from different experiments when relations are used which were derived assuming non-interacting electrons [1].
Photoemission experiments on undoped cuprates indicate polaronic coupling between bosons and charge carriers. We calculate the electron-phonon interaction within a shell model and find it sufficiently strong to give polaronic behavior. Using an adiabatic approximation we explain why the broad phonon side band disperses like the quasi-particle in a purely electronic model without electron-phonon interaction [2]. We develop an efficient method for calculating ARPES spectra in undoped systems. Width and binding energy of the phonon side band are found in reasonable agreement with experiment using the calculated coupling for La2CuO4. We analyze reasons for the observed dependence of the width on the binding energy and discuss the temperature dependence. [1] O. Rösch and O. Gunnarsson, Phys. Rev. Lett. 92, 146403 (2004). [2] O. Rösch and O. Gunnarsson, Eur. Phys. J. B 43, 11 (2005). |