Roles of Hund's rule coupling in excitonic density-wave states

TL;DR

This study investigates how Hund's rule coupling influences excitonic density-wave states in a two-band Hubbard model, revealing that it stabilizes spin-density-wave states while destabilizing charge-density-wave states, with implications for material properties.

Contribution

The paper demonstrates the specific effects of Hund's rule coupling and pair hopping on excitonic density-wave states using variational cluster approximation.

Findings

Hund's rule coupling stabilizes excitonic spin-density-wave states

Hund's rule coupling destabilizes excitonic charge-density-wave states

Pair hopping enhances these effects

Abstract

Excitonic density-wave states realized by the quantum condensation of electron-hole pairs (or excitons) are studied in the two-band Hubbard model with Hund's rule coupling and the pair hopping term. Using the variational cluster approximation, we calculate the grand potential of the system and demonstrate that Hund's rule coupling always stabilizes the excitonic spin-density-wave state and destabilizes the excitonic charge-density-wave state and that the pair hopping term enhances these effects. The characteristics of these excitonic density-wave states are discussed using the calculated single-particle spectral function, density of states, condensation amplitude, and pair coherence length. Implications of our results in the materials' aspects are also discussed.