Saturating T squared resistivity in iron-based superconductors

Many correlated metals exhibit a crossover from low-temperature ρ proportional to T squared behavior to a slower increase of the resistivity at elevated temperatures. Distinguishing phonon scattering from electron--electron correlations as the origin of this crossover is experimentally challenging. We introduce a simple phenomenological framework that isolates the contribution responsible for the high-temperature saturating tendency. This approach reveals a clear contrast between systems well known for the predominance of electron--phonon scattering and several iron-based superconductors. For the latter, the conductivity can be expressed as the sum of a Fermi-liquid-like term (proportional to 1/T squared) and a temperature-independent component, which together describe ρ(T) up to about 250 K in LiFeAs, KFe 2 As 2, and KCaFe 4 As 4. In FeSe, the same approach identifies a similar regime above the nematic transition, with a pronounced change toward nearly linear-in- T resistivity below it. We discuss these findings in the broader context of coherence and electronic correlations in Hund's metals.