Phase Diagrams of the Excitonic Insulator State: Analyzing the Excitonic Susceptibility

Abstract

In this paper, the formation of the excitonic insulator state in the rare-earth chalcogenides has
been investigated through the extended Falicov-Kimball model. Adapting the unrestricted Hartree-Fock
approximation, we have derived a set of explicitly self-consistent equations determining expectation
values and the excitonic susceptibility in the system. Analyzing the excitonic susceptibility, we have
established phase diagrams of the excitonic insulator state depending on the model parameters. The phase
structures confirmed the excitonic insulator state is found at low temperature and between two critical
values of the Coulomb interaction. The effect of the external pressure on the formation of the excitonic
insulator state is also shown.