Momentum Dependence of the Electron-Phonon Coupling and Self-Energy Effects in Superconducting YBa₂Cu₃O₇ within the Local Density Approximation

Using the local density approximation and a realistic phonon spectrum we determine the momentum and frequency dependence of α²F(k,ω) in YBa₂Cu₃O₇ for the bonding, antibonding, and chain band. The resulting self-energy Σ is rather small near the Fermi surface. For instance, for the antibonding band the maximum of ReΣ as a function of frequency is about 7 meV at 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 Σ can be attributed to phonons. Furthermore, the frequency dependence of the renormalization factor Z(k,ω) 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.