First-principles calculations reveal an unusual electronic state (dubbed as half excitonic insulator) in monolayer 1T-MX2 (M = Co, Ni and X = Cl, Br). Its one spin channel has a many-body ground state due to excitonic instability, while the other is characterized by a conventional band insulator gap. This disparity arises from a competition between the band gap and exciton binding energy, which exhibits a spin-dependence due to different orbital occupations. Such a state can be identified by optical absorption measurements and angle-resolved photoemission spectroscopy. Our theory not only provides new insights for the study of exciton condensation in magnetic materials but also suggests that strongly-correlated materials could be fertile candidates for excitonic insulators.
@article{arxiv.1811.03738,
title = {Half Excitonic Insulator: A Single-Spin Bose-Einstein Condensate},
author = {Zeyu Jiang and Yuanchang Li and Wenhui Duan and Shengbai Zhang},
journal= {arXiv preprint arXiv:1811.03738},
year = {2019}
}