Kinks cannot be ascribed to phonons

In cuprate superconductors, the dispersion of energy with wave vectors features some kinks. As regards the cause of such kinks, suppliers with phonons has appeared. However, this paper [http://www.fkf.mpg.de/metzner/manske/Pub/PRL100_137001.pdf] disfavors such choice.

Using the local density approximation and a realistic phonon spectrum we determine the momentum and frequency dependence of 2F k;! in YBa2Cu3O7 for the bonding, antibonding, and chain band. The resulting self-energy is rather small near the Fermi surface. For instance, for the antibonding band the maximum of Re as a function of frequency is about 7 meVat the nodal point in the normal state and the ratio of bare and renormalized Fermi velocities is 1.18. These values are a factor of 3–5 too small compared to the experiment showing that only a small part of can be attributed to phonons. Furthermore, the frequency dependence of the renormalization factor Z k;! is smooth and has no anomalies at the observed kink frequencies which means that phonons cannot produce well-pronounced kinks in stoichiometric YBa2Cu3O7, at least, within the local density approximation.