First-principles density functional theory plus Bethe-Salpeter equation calculations are employed to investigate the electronic and excitonic properties of monolayer titanium trichalcogenide alloys TiS3−xSex (x=1 and 2). It is found that bandgap and exciton binding energy display asymmetric dependence on the substitution of Se for S. While the bandgap can be significantly decreased as compared to that of pristine TiS3, the exciton binding energy just varies a little, regardless of position and concentration of the Se substitution. A negative exciton formation energy is found when the central S atoms are replaced by Se atoms, suggesting a many-body ground state with the spontaneous exciton condensation. Our work thus offers a new insight for engineering an excitonic insulator.
@article{arxiv.2009.12805,
title = {Transition from band insulator to excitonic insulator via alloying Se into Monolayer TiS$_3$: A Computational Study},
author = {Shan Dong and Yuanchang Li},
journal= {arXiv preprint arXiv:2009.12805},
year = {2020}
}