We employ the multi-orbital dynamical mean-field theory to examine the ground state of a three-orbital Hubbard model with a relativistic spin-orbit coupling (SOC) at four electrons per site. We demonstrate that the interplay between the strong electron correlations and the SOC induces a Van Vleck-type nonmagnetic insulator and its magnetic exciton condensation. We also find in the moderate electron correlation regime that the SOC induces another type of a nonmagnetic excitonic insulator, in addition to a relativistic band insulator. The characteristic features among these insulators are manifested in the momentum resolved single-particle excitations, thus accessible by angle-resolved photoemission spectroscopy experiments.
@article{arxiv.1603.01800,
title = {Spin-Orbital Entangled Excitonic Insulators in $(t_{2g})^4$ Correlated Electron Systems},
author = {Toshihiro Sato and Tomonori Shirakawa and Seiji Yunoki},
journal= {arXiv preprint arXiv:1603.01800},
year = {2019}
}