Is LaO$_{1-x}$F$_x$FeAs an electron-phonon superconductor ?

TL;DR

This study uses first-principles calculations to evaluate whether electron-phonon interactions can explain superconductivity in LaO$_{1-x}$F$_x$FeAs, concluding they are insufficient and suggesting strong correlations are involved.

Contribution

It provides the first detailed first-principles analysis of electron-phonon coupling in LaO$_{1-x}$F$_x$FeAs, showing it cannot account for the high superconducting transition temperature.

Findings

Electron-phonon coupling constant $mbda=0.21$ for pure LaOFeAs.

Predicted maximum $T_c$ from phonons alone is about 0.8 K.

Electron-phonon coupling is too weak to explain the observed $T_c=26$ K.

Abstract

In this paper we calculate the electron-phonon coupling of the newly-discovered superconductor LaO$_{1-x}$F$_x$FeAs from first-principles, using Density Functional Perturbation Theory. For pure LaOFeAs, the calculated electron-phonon coupling constant $\lambda=0.21$ and logarithmic-averaged frequency $\omega_{ln}=206 K$, give a maximum $T_c$ of 0.8 K, using the standard Migdal-Eliashberg theory. For the $F-$doped compounds, we predict even smaller coupling constants, due to the strong suppression of the electronic Density of States at the Fermi level. To reproduce the experimental $T_c=26 K$, a 5-6 times larger coupling constant would be needed. Our results indicate that electron-phonon coupling is not sufficient to explain superconductivity in the newly-discovered LaO$_{1-x}$F$_x$FeAs superconductor, probably due to the importance of strong correlation effects.