  We report an angle-resolved photoemission study of a series of hole and
electron doped iron-based superconductors, their parent compound BaFe2As2, and
their cousins BaCr2As2 and BaCo2As2. We focus on the energy (E) dependent
scattering rate Gamma(E) as a function of the 3d count and on the
renormalization function Z(E) of the inner hole pocket, which is the hot spot
in these compounds. We obtain a non-Fermi-liquid-like linear in energy
scattering rate Gamma(E>> kBT), independent of the dopant concentration. The
main result is that the slope beta=Gamma(E >> kBT)/E, reaches its maxima near
optimal doping and scales with the superconducting transition temperature. This
supports the spin fluctuation model for superconductivity for these materials.
In the optimally hole-doped compound, the slope of the scattering rate of the
inner hole pocket is about three times bigger than the Planckian limit
Gamma(E)/E~1. This result together with the energy dependence of the
renormalization function Z(E) signals very incoherent charge carriers in the
normal state which transform at low temperatures to a coherent unconventional
superconducting state.
