Exciton condensation in a two-band Hubbard model on a square lattice is studied with variational Monte Carlo method. We show that the phase transition from an excitonic insulator to a band insulator is induced by increasing the interband Coulomb interaction. To examine the character of the exciton condensation, the exciton pair amplitudes both in k-space and in real space are calculated. Using these quantities, we discuss the BCS-BEC crossover within the excitonic insulator phase.
@article{arxiv.1505.02208,
title = {A variational Monte Carlo study of exciton condensation},
author = {Hiroshi Watanabe and Kazuhiro Seki and Seiji Yunoki},
journal= {arXiv preprint arXiv:1505.02208},
year = {2015}
}