Using the projector-based renormalization method we investigate the formation of the excitonic insulator phase in the two-dimensional (2D) spinless Falicov-Kimball model with dispersive f electrons and address the existence of excitonic bound states at high temperatures on the semiconductor side of the semimetal-semiconductor transition. To this end we calculate the imaginary part of the dynamical electron-hole pair susceptibility and analyze the wave-vector and energy dependence of excitonic resonances emerging in the band gap. We thereby confirm the existence of the exciton insulator and its exciton environment within a generic two-band lattice model with local Coulomb attraction.
@article{arxiv.1102.0837,
title = {Excitonic resonances in the 2D extended Falicov-Kimball model},
author = {Van-Nham Phan and Holger Fehske and Klaus W. Becker},
journal= {arXiv preprint arXiv:1102.0837},
year = {2015}
}