  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.

Strongly Correlated Electrons