Anomalous magneto-elastic coupling in Au-doped BaFe2As2

Authors:  S.-F. Wu, W.-L. Zhang, L. Li, H.-B. Cao, H.-H. Kung, A. S. Sefat, H. Ding, P. Richard, and G. Blumberg

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We used polarization-resolved Raman scattering to study magneto-elastic coupling in Ba(Fe1-xAux)2As2 crystals as a function of light Au-doping, materials for which temperatures of the structural transition (TS) and of the magnetic ordering transition (TN) split. We study the appearance of the Ag (As)phonon intensity in the XY scattering geometry that is very weak just below TS, but for which the intensity is significantly enhanced below TN. In addition, the Ag (As) phonon shows an asymmetric line shape below TN and an anomalous linewidth broadening upon Au-doping in the magnetic phase. We demonstrate that the anomalous behavior of the Ag (As) phonon mode in the XY scattering geometry can be consistently described by a Fano model involving the Ag (As) phonon mode interacting with the B2g symmetry-like magnetic continuum in which the magneto-elastic coupling constant is proportional to the magnetic order parameter.