Electronic correlations in Hund metals

TLDR

The study aims to clarify how electronic correlations in Hund metals relate to Mott physics by analyzing multiorbital systems across varying intraorbital interaction U, Hund coupling J_H, and electronic filling n. The authors analyze multiorbital correlations as functions of U, J_H, and n, and use simple energetic arguments to show that Hund’s coupling induces spin polarization that decouples orbitals. They find that correlation enhancement in Hund metals is driven by suppressed double occupancy, that quasiparticle weight and mass enhancement poorly reflect charge localization, and that the system transitions from spin‑polarization–controlled correlations at moderate interactions to Mott‑like behavior at large U and J_H.

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 ${J}_{H}$, 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 ${J}_{H}$ can happen in 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.