Quadratic band crossing points (QBCPs) and quantum anomalous Hall effect (QAHE) have attracted the attention of both theoretical and experimental researchers in recent years. Based on first-principle calculations, we find that the FeB2 monolayer is a nonmagnetic semimetal with QBCPs at K. Through symmetry analysis and k⋅p invariant theory, we find that the QBCP is not protected by rotation symmetry and consists of two Dirac points with same chirality (Berry phase of 2π). Once introducing Coulomb interactions, we find that there is a spontaneous-time-reversal-breaking instability of the spinful QBCPs, which gives rise to a C=2 QAH insulator with orbital moment ordering.
@article{arxiv.2110.11058,
title = {Unprotected quadratic band crossing points and quantum anomalous Hall effect in FeB2 monolayer},
author = {Dongyu Wu and Yunpeng Huang and Song Sun and Jiacheng Gao and Zhaopeng Guo and Hongming Weng and Zhong Fang and Kun Jiang and Zhijun Wang},
journal= {arXiv preprint arXiv:2110.11058},
year = {2022}
}