Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsO$_{x}$F$_{1-x}$ single crystals

TL;DR

This study investigates how temperature and resonance effects influence Raman scattering of phonons in NdFeAsO$_{x}$F$_{1-x}$ single crystals, revealing weak phonon-electron coupling and resonance enhancement linked to interband transitions.

Contribution

It provides the first detailed analysis of temperature dependence and resonance effects in Raman spectra of NdFeAsO$_{x}$F$_{1-x}$, highlighting weak phonon-electron interactions.

Findings

Phonon lines are sharp and symmetrical with weak doping dependence.

No phonon anomalies at the superconducting transition temperature.

Resonant enhancement of Fe phonon intensity below 2 eV linked to interband transitions.

Abstract

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.