Electronic correlations in Hund metals

Abstract

To clarify the nature of correlations in Hund metals and its relationship with Mott physics we analyze the electronic correlations in multiorbital systems as a function of intraorbital interaction U, Hund's coupling JH and electronic filling n. We show that the main process behind the enhancement of correlations in Hund metals is the suppression of the double-occupancy of a given orbital, as it also happens in the Mott-insulator at half-filling. However, contrary to what happens in Mott correlated states the reduction of the quasiparticle weight Z with JH can happen on spite of increasing charge fluctuations. Therefore, in Hund metals the quasiparticle weight and the mass enhancement are not good measurements of the charge localization. Using simple energetic arguments we explain why the spin polarization induced by Hund's coupling produces orbital decoupling. We also discuss how the behavior at moderate interactions, with correlations controlled by the atomic spin polarization, changes at large $U$ and $J_H$ due to the proximity to a Mott insulating state.