Evidence of Electron-phonon Interaction in the Infrared Spectra of Oxide Superconductors

We show that the structure in ab-plane infrared spectra of the oxide superconductors can be understood in terms of the electron-phonon interaction. The minima in the optical conductivity seen in the oxygen breathing mode region translate to peaks in the frequency dependent scattering rate. The position and the width of the peaks are in reasonable agreement with structure seen in timeof-flight neutron spectroscopy. We interpret the appearance of phonon modes in the highly metallic ab-plane in terms of a charged phonon model borrowed from the theory of organic conductors.