Magneto-elastic coupling in Fe-based superconductors

TL;DR

This study investigates magneto-elastic interactions in Fe-based superconductors using Raman scattering, revealing magnetic order-dependent phonon behavior and strong electron-phonon coupling potentially relevant to superconductivity.

Contribution

It provides new insights into the magneto-elastic coupling mechanisms and phonon-electron interactions in Fe-based superconductors through polarization-resolved Raman spectroscopy.

Findings

Emergent Ag-symmetry As phonon mode enhanced below magnetic transition

Lattice anisotropy alone does not cause phonon intensity changes

Strong electron-phonon coupling observed via Fano line-shape

Abstract

We used polarization-resolved Raman scattering to study the magneto-elastic coupling in the parent compounds of several families of Fe-based superconductors (BaFe2As2, EuFe2As2, NaFeAs, LiFeAs, FeSe and LaFeAsO). We observe an emergent Ag-symmetry As phonon mode in the XY scattering geometry whose intensity is significantly enhanced below the magneto-structural transition only for compounds showing magnetic ordering. We conclude that the small lattice anisotropy is insufficient to induce the in-plane electronic polarizability anisotropy necessary for the observed phonon intensity enhancement, and interpret this enhancement below the Neel temperature in terms of the anisotropy of the magnetic moment and magneto-elastic coupling. We evidence a Fano line- shape in the XY scattering geometry resulting from a strong coupling between the Ag (As) phonon mode and the B2g symmetry-like electronic continuum. Strong electron-phonon coupling may be relevant to superconductivity.