Electronic correlations in Hund metals

TL;DR

This paper investigates the nature of electronic correlations in Hund metals, revealing how Hund's coupling influences quasiparticle weight, charge fluctuations, and orbital decoupling, and clarifies their relationship with Mott physics.

Contribution

It provides a detailed analysis of correlation effects in multiorbital systems, highlighting the distinct roles of Hund's coupling and Mott physics, and explains the mechanisms behind orbital decoupling and correlation enhancement.

Findings

Suppression of double-occupancy drives correlation enhancement in Hund metals.

Quasiparticle weight reduction can occur despite increasing charge fluctuations.

Hund's coupling induces orbital decoupling through spin polarization effects.

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.