Microscopic nature of correlations in multi-orbital AFe2As2 (A=K, Rb, Cs): Hund's coupling versus Coulomb repulsion

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We investigate via LDA+DMFT (local density approximation combined with dynamical mean field theory) the manifestation of correlation effects in a wide range of binding energies in the hole-doped family of Fe-pnictides AFe₂As₂ (A= K, Rb, Cs) as well as the fictitious FrFe₂As₂ and a-axis stretched CsFe₂As₂. This choice of systems allows for a systematic analysis of the interplay of Hund's coupling Jₕ and on-site Coulomb repulsion U in multi-orbital Fe-pnictides under negative pressure. With increasing ionic size of the alkali metal, we observe a non-trivial change in the iron 3d hoppings, an increase of orbitally-selective correlations and the presence of incoherent weight at high-binding energies that do not show the typical lower Hubbard-band behavior but rather characteristic features of a Hund's metal. This is especially prominent in a-stretched CsFe₂As₂. We also find that the coherent/incoherent electronic behavior of the systems is, apart from temperature, strongly dependent on Jₕ and we provide estimates of the coherence scale T*. We discuss these results in the framework of reported experimental observations.