Phonon Damping in YBaCuO: Simplicity of a Complex System

We report a study of the phonon spectra in YBa2Cu3O7—x single crystals with varied oxygen content. We have experimentally investigated the temperature dependence of the widths of phonon Raman lines, including the resonantly enhanced additional ones. Upon comparing our results with those from studies of infrared-active phonons, we have found that the phonon dampings over whole spectral range and a wide range of temperatures can be described in a framework of a rather simple model despite the intricacy of the phonon anharmonicity phenomenon and the complexity of the multi-atom unit cell of YBa2Cu3O7—x. We attribute such a simplification to the effective averaging of the phonon–phonon interaction, which is both wave-vector- and energy-dependent due to the large number of phonons involved.