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

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 multiorbital Fe pnictides under negative pressure. With increasing ionic size of the alkali metal, we observe a nontrivial 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 ab-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.