Anharmonic softening of Raman active phonons in Iron-Pnictides; estimating the Fe isotope effect due to anharmonic expansion

Abstract

We present Raman measurements on the iron-pnictide superconductors CeFeAsO_{1-x}F_{x} and NdFeAsO{1-x}F_{x}. Modeling the Fe-As plane in terms of harmonic and a cubic anharmonic Fe-As interaction we calculate the temperature dependence of the energy and lifetime of the Raman active Fe B_{1g} mode and fit to the observed energy shift. The shifts and lifetimes are in good agreement with those measured also in other Raman studies which demonstrate that the phonon spectrum is well represented by phonon-phonon interactions without any significant electronic contribution. We also estimate the anharmonic expansion from Fe (56->54) isotope substitution to Δa=5.1 10^{-4}Åand Δd_{Fe-As}= 2.510^{-4}Åand the shift of harmonic zero point fluctuations of bond lengths <Δx^2><=3 10^{-5}Å^2, giving a total relative average decrease of electronic hopping integrals of |δt|/t<= 2.0 10^{-4}. The results poses a serious challenge for any theory of superconductivity in the pnictides that does not include electron-phonon interactions to produce a sizable Fe-isotope effect.

arXiv comment7 pages, 6 figures

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Cited by in corpus (8)

• FeAs-based superconductivity: a case study of the effects of transition metal doping on BaFe2As2
• Anomalous optical phonons in FeTe pnictides: spin state, magnetic order, and lattice anharmonicity
• Intrinsic and structural isotope effects in Fe-based superconductors
• Self-energy effects and electron-phonon coupling in Fe-As superconductors
• Small-q Phonon Mediated Unconventional Superconductivity in the Iron Pnictides
• Soft and Isotropic Phonons in PrFeAsO_{1-y}
• Raman scattering in iron-based superconductors
• Lattice expansion from isotope substitution in the Iron based superconductors