Phonon Density of States in Nd(O$_{1-x}$F$_{x}$)FeAs

TL;DR

This study measures the phonon density of states in Nd(O$_{1-x}$F$_{x}$)FeAs superconductors, revealing phonon softening with F doping and comparing experimental results with theoretical calculations.

Contribution

It provides experimental phonon density-of-states data in iron oxypnictide superconductors and uncovers doping-induced phonon softening not predicted by standard ab-initio models.

Findings

Good agreement with ab-initio calculations without strong electronic correlations

Unpredicted phonon softening under F doping

Softening occurs at finite momentum transfer, not zone center

Abstract

We report measurements of the phonon density-of-states in iron oxypnictide superconductors by inelastic x-ray scattering. A good agreement with ab-initio calculations that do not take into account strong electronic correlations is found, and an unpredicted softening of phonon branches under F doping of these compounds is observed. Raman scattering experiments lead us to conclude that this softening is not related to zone center phonons, and consequently imply an important softening of the relevant phonon branches at finite momentum transfer Q.