Experimental evidence for importance of Hund's exchange interaction for incoherence of charge carriers in iron-based superconductors

Angle-resolved photoemission spectroscopy is used to study the scattering rates of charge carriers from the hole pockets near Gamma in the iron-based high-T-c hole-doped superconductors K-x Ba1-x Fe2As2, x = 0.4, and K-x Eu1-x Fe2As2, x = 0.55, and the electron-doped compound Ba(Fe1-x Co-x)(2)As-2, x = 0.075. The scattering rate for any given band is found to depend linearly on the energy, indicating a non-Fermi-liquid regime. The scattering rates in the hole-doped compound are considerably higher than those in the electron-doped compounds. In the hole-doped systems the scattering rate of the charge carriers of the inner hole pocket is about three times higher than the binding energy, indicating that the spectral weight is heavily incoherent. The strength of the scattering rates and the difference between electron-and hole-doped compounds signals the importance of Hund's exchange coupling for correlation effects in these iron-based high-T-c superconductors. The experimental results are in qualitative agreement with theoretical calculations in the framework of combined density functional dynamical mean-field theory.