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Eliashberg analysis of optical spectra reveals a strong coupling of charge carriers to spin fluctuations in doped iron-pnictide BaFe2As2 superconductors

The temperature and frequency dependences of the optical conductivity of Co-doped BaFe2As2 are analyzed and the electron-boson spectral density
2F
 are extracted using Eliashberg’s formalism. For the normal state at T=30 K there is a relatively sharp and large peak around 10 meV and a secondary smaller and broader peak centered around 50 meV with the spectrum extending to high energies beyond the maximum phonon energy. The electron-boson mass enhancement parameter is 4.4, a value more consistent with spin-fluctuation scattering rather than with phonons. In addition the spectrum is found to evolve with temperature toward a less structured background at higher energies as in the spin susceptibility.

PACS number
s: 74.25.Gz; 74.20.Mn; 74.20.Rp; 74.70.Xa

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