Inelastic x-ray scattering investigations of lattice dynamics in SmFeAsO$_{1-x}$F$_y$ superconductors

TL;DR

This study uses inelastic x-ray scattering to investigate lattice dynamics in SmFeAsO$_{1-x}$F$_y$ superconductors, revealing phonon renormalization linked to fluorine substitution and potential electron-phonon interactions.

Contribution

First measurement of phonon density of states and dispersion in SmFeAsO$_{1-x}$F$_y$ superconductors, identifying specific phonon modes affected by fluorine doping.

Findings

Strong phonon renormalization around 23 meV with fluorine substitution

Identification of specific phonon modes responsible for renormalization

Evidence suggesting unusual electron-phonon coupling in these materials

Abstract

We report measurements of the phonon density of states as measured with inelastic x-ray scattering in SmFeAsO$_{1-x}$F$_y$ powders. An unexpected strong renormalization of phonon branches around 23 meV is observed as fluorine is substituted for oxygen. Phonon dispersion measurements on SmFeAsO$_{1-x}$F$_y$ single crystals allow us to identify the 21 meV A$_{1g}$ in-phase (Sm,As) and the 26 meV B$_{1g}$ (Fe,O) modes to be responsible for this renormalization, and may reveal unusual electron-phonon coupling through the spin channel in iron-based superconductors.