Electronic Raman scattering of antiferromagnetic excitonic insulators

TL;DR

This paper proposes Raman spectroscopy as an effective method to detect exciton condensation in correlated transition metal oxides, and demonstrates its application in identifying exciton condensation in Sr₃Ir₂O₇ under pressure.

Contribution

It develops a mean field Raman operator for the Hubbard model and applies it to show how Raman scattering reveals exciton condensation in a specific material.

Findings

Raman scattering can directly detect exciton condensation.

Application to Sr₃Ir₂O₇ under pressure confirms excitonic state.

Provides a theoretical framework linking Raman spectra to exciton order.

Abstract

The excitonic insulator, a quantum mechanical state arising from exciton condensation, was proposed theoretically many years ago but has yet to be experimentally confirmed. The discovery of correlated transition metal oxides based on $4d$ and $5d$ elements, where the on-site Coulomb repulsion is comparable to the dominant hopping amplitude, presents a unique opportunity to study exciton condensation. By constructing an effective mean field Raman operator for the Hubbard model, we derive the low-energy electronic Raman scattering cross section, demonstrating Raman spectroscopy as a powerful tool for detecting exciton condensation. Here, we demonstrate that Raman scattering directly reveals exciton condensation in the bilayer iridate Sr$_3$Ir$_2$O$_7$ under pressure.