Electron-Phonon Properties of Pnictide Superconductors

TL;DR

This study uses theoretical calculations to analyze electron-phonon interactions in pnictide superconductors, finding that standard electron-phonon coupling explains Ni-As compounds but is insufficient for Fe-As based superconductors.

Contribution

It provides a detailed theoretical analysis of electron-phonon properties in LaOFeAs and LaONiAs, highlighting the limitations of phonon-mediated pairing in Fe-As superconductors.

Findings

Electron-phonon coupling in LaOFeAs is too weak to account for observed Tc.

Ni-As compounds exhibit stronger electron-phonon coupling consistent with experimental data.

Standard Migdal-Eliashberg theory describes Ni-As compounds well, but not Fe-As superconductors.

Abstract

In this paper we discuss the normal and superconducting state properties of two pnictide superconductors, LaOFeAs and LaONiAs, using Migdal-Eliashberg theory and 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. Inclusion of multiband effects increases the Tc only marginally. To reproduce the experimental $T_c$, a 5-6 times larger coupling constant would be needed. Our results indicate that standard electron-phonon coupling is not sufficient to explain superconductivity in the whole family of Fe-As based superconductors. At the same time, the electron-phonon coupling in Ni-As based compounds is much stronger and its normal and superconducting state properties can be well described by standard Migdal-Eliashberg theory.