Inelastic X-ray scattering investigations of lattice dynamics in SmFeAsO1−xFysuperconductors

We report measurements of the phonon density of states as probed with inelastic X-ray scattering in SmFeAsO1−xFy powders. An unexpected strong renormalization of phonon branches around 23 meV is observed as fluorine is substituted for oxygen. Phonon dispersion measurements on SmFeAsO1−xFy single crystals allow us to identify the 21 meV A1g in-phase (Sm,As) and the 26 meV B1g (Fe,O) modes to be responsible for this renormalization, and may reveal unusual electron–phonon coupling through the spin channel in iron-based superconductors.