Nonlocal Coulomb interaction and spin-freezing crossover as a route to valence-skipping charge order

TL;DR

This paper demonstrates that nonlocal Coulomb interactions induce valence-skipping charge order in a three-orbital model, with the transition being significantly enhanced during the spin-freezing crossover regime, revealing new insights into Hund's metals.

Contribution

It shows that intersite Coulomb interaction drives charge order and that this effect is amplified in the spin-freezing crossover, linking atomic multiplet populations to charge instability in Hund's metals.

Findings

Charge order transition driven by intersite Coulomb interaction V.

Enhanced instability in the spin-freezing crossover regime.

Atomic multiplet populations influence charge order formation.

Abstract

Multiorbital systems away from global half-filling host intriguing physical properties promoted by Hund's coupling. Despite increasing awareness of this regime dubbed Hund's metal, effect of nonlocal interaction is still elusive. Here we study a three-orbital model with $1/3$ filling (two electrons per site) including the intersite Coulomb interaction ($V$). Using the $GW$ plus extended dynamical mean-field theory, the valence-skipping charge order transition is shown to be driven by $V$. Most interestingly, the instability to this transition is significantly enhanced in the spin-freezing crossover regime, thereby lowering the critical $V$ to the formation of charge order. This behavior is found to be closely related to the population profile of the atomic multiplet states in the spin-freezing regime. In this regime, maximum spin states are dominant in each total charge subspace with substantial amount of one- and three-electron occupations, which leads to almost equal population of one- and the maximum spin three-electron state. Our finding unveils another feature of the Hund's metal, and has potential implications for the broad range of multiorbital systems as well as the recently discovered charge order in iron-pnictides.