Momentum dependence of the electron-phonon coupling and self-energy effects in YBa_2Cu_3O_7 within the local density approximation

TL;DR

This study uses LDA calculations to analyze the momentum and frequency dependence of electron-phonon interactions in YBa2Cu3O7, finding that phonons contribute only a small part to the observed self-energy effects and cannot explain the prominent kinks.

Contribution

It provides a detailed LDA-based analysis of electron-phonon coupling in YBa2Cu3O7, highlighting its limited role in self-energy effects and kink phenomena.

Findings

Self-energy $ ext{Re}\Sigma$ is small (~7 meV) near the Fermi surface.

Phonons account for only a small part of the experimentally observed self-energy.

No anomalies at kink frequencies suggest phonons do not produce pronounced kinks within LDA.

Abstract

Using the local density approximation (LDA) and a realistic phonon spectrum we determine the momentum and frequency dependence of $\alpha^2F({\bf k},\omega)$ in YBa$_2$Cu$_3$O$_7$ for the bonding, antibonding, and chain band. The resulting self-energy $\Sigma$ is rather small near the Fermi surface. For instance, for the antibonding band the maximum of $Re \Sigma$ 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 1.18. These values are a factor 3-5 too small compared to the experiment showing that only a small part of $\Sigma$ can be attributed to phonons. Furthermore, the frequency dependence of the renormalization factor $Z({\bf k},\omega)$ is smooth and has no anomalies at the observed kink frequencies which means that phonons cannot produce well-pronounced kinks in stoichiometric YBa$_2$Cu$_3$O$_7$, at least, within the LDA.