Correlation induced spin freezing transition in FeSe and FeAsLaO: a dynamical mean field study

Dynamical mean field theory (DMFT) combined with finite-temperature exact diagonalization (ED) has recently been used to study the role of Coulomb interactions in several transition metal oxides and other strongly correlated materials. The focus here is on iron pnictides and chalcogenides. Although compounds such as FeAsLaO and FeSe have similar one-electron properties, experiments suggest significant differences. Evaluating the effect of Coulomb correlations within ED/DMFT we show that in FeSe the formation of 3d local moments gives rise to non-Fermi-liquid behavior. In FeAsLaO Coulomb interactions are not strong enough to cause spin freezing, so that this compound merely exhibits moderate effective mass enhancement. The relation between these kinds of multi-orbital correlations and multi-site correlations that are important in high-T_c cuprates will also be addressed.