Normal state resistivity of Ba$_{1-x}$K$_x$Fe$_2$As$_2$: evidence for multiband strong-coupling behavior

We present theoretical analysis of the normal state resistivity in multiband superconductors in the framework of Eliashberg theory. The results are compared with measurements of the temperature dependence of normal state resistivity of high-purity Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ single crystals with the highest reported transition temperature $T_c = 38.5$ K. The experimental data demonstrate strong deviations from the Bloch–Grüneisen behavior, namely the tendency to saturation of the resistivity at high temperatures. The observed behavior of the resistivity is explained within the two band scenario when the first band is strongly coupled and relatively clean, while the second band is weakly coupled and is characterized by much stronger impurity scattering.