Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsOxF1-x single crystals

We report plane-polarized Raman-scattering spectra of iron oxypnictide superconductor NdFeAsO(1-x)F(x) single crystals with varying fluorine x content. The spectra exhibit sharp and symmetrical phonon lines with a weak dependence on fluorine doping x. The temperature dependence does not show any phonon anomaly at the superconducting transition. The Fe related phonon intensity shows a strong resonant enhancement below 2 eV. We associate the resonant enhancement to the presence of an interband transition around 2 eV observed in optical conductivity. Our results point to a rather weak coupling between Raman-active phonons and electronic excitations in iron oxypnictides superconductors.