Quantum spin-hall insulator (QSHI) processes nontrivial topology. We notice that the electronic structures of some particular QSHIs are favorable for realization of excitonic insulators (EIs). Using first-principles many-body perturbation theory (GW+BSE) and k⋅p model, we show that high-temperature (T) topological EIs with unlike spin can exist in such QSHIs with non-vanishing band gaps, e.g. 2D AsO and Mo2TiC2O2. Spin-triplet type EI phase induced by strong electron-hole interaction preserves time-reversal symmetry and the topological characteristics. A novel optical selection rule exists, upon going through the phase transition from the normal QSHIs to the topological EIs, absorption spectroscopy shows pronounced T-dependent changes, providing guidance for future experimental detections. The demonstrated coupling between EIs and topology also means that rich physics exists in such materials which retain such interdisciplinary features.
@article{arxiv.2304.00463,
title = {Spin-Triplet Topological Excitonic Insulators in Two-dimensional Materials},
author = {Huaiyuan Yang and Jiaxi Zeng and Yuelin Shao and Yuanfeng Xu and Xi Dai and Xin-Zheng Li},
journal= {arXiv preprint arXiv:2304.00463},
year = {2023}
}