Topological magnets are a new family of quantum materials providing great potential to realize emergent phenomena, such as quantum anomalous Hall effect and axion-insulator state. Here we present our discovery that stoichiometric ferromagnet MnBi8Te13 with natural heterostructure MnBi2Te4-(Bi2Te3)3 is an unprecedented half-magnetic topological insulator, with the magnetization existing at the MnBi2Te4 surface but not at the opposite surface terminated by triple Bi2Te3 layers. Our angle-resolved photoemission spectroscopy measurements unveil a massive Dirac gap at the MnBi2Te4 surface, and gapless Dirac cone on the other side. Remarkably, the Dirac gap (~28 meV) at MnBi2Te4 surface decreases monotonically with increasing temperature and closes right at the Curie temperature, thereby representing the first smoking-gun spectroscopic evidence of magnetization-induced topological surface gap among all known magnetic topological materials. We further demonstrate theoretically that the half-magnetic topological insulator is desirable to realize the half-quantized surface anomalous Hall effect, which serves as a direct proof of the general concept of axion electrodynamics in condensed matter systems.
@article{arxiv.2009.04140,
title = {Half-Magnetic Topological Insulator},
author = {Ruie Lu and Hongyi Sun and Shiv Kumar and Yuan Wang and Mingqiang Gu and Meng Zeng and Yu-Jie Hao and Jiayu Li and Jifeng Shao and Xiao-Ming Ma and Zhanyang Hao and Ke Zhang and Wumiti Mansuer and Jiawei Mei and Yue Zhao and Cai Liu and Ke Deng and Wen Huang and Bing Shen and Kenya Shimada and Eike F. Schwier and Chang Liu and Qihang Liu and Chaoyu Chen},
journal= {arXiv preprint arXiv:2009.04140},
year = {2021}
}