Half-Magnetic Topological Insulator with Magnetization-Induced Dirac Gap at a Selected Surface
Ruie Lu, Hongyi Sun, Shiv Kumar, Yuan Wang, Mingqiang Gu, Meng Zeng, Yu‐Jie Hao, Jiayu Li, Jifeng Shao, Xiao‐Ming Ma, Zhanyang Hao, Ke Zhang, Wumiti Mansuer, Jia‐Wei Mei, Yüe Zhao, Cai Liu, Ke Deng, Wen Huang, Bing Shen, K. Shimada, Eike F. Schwier, Chang Liu, Qihang Liu, Kai Chen
Abstract
Topological magnets are a new family of quantum materials providing great potential to realize emergent phenomena, such as the quantum anomalous Hall effect and the axion-insulator state. Here, we present our discovery that the stoichiometric ferromagnet MnBi 8 Te 13 with natural heterostructure MnBi 2 Te 4 =Bi 2 Te 3 3 is an unprecedented "half-magnetic topological insulator," with the magnetization existing at the MnBi 2 Te 4 surface but not at the opposite surface terminated by triple Bi 2 Te 3 layers. Our angle-resolved photoemission spectroscopy measurements unveil a massive Dirac gap at the MnBi 2 Te 4 surface and a gapless Dirac cone on the other side. Remarkably, the Dirac gap (about 28 meV) at the MnBi 2 Te 4 surface decreases monotonically with increasing temperature and closes right at the Curie temperature, thereby representing the first smoking-gun spectroscopic evidence of a magnetizationinduced topological surface gap among all known magnetic topological materials. We further demonstrate theoretically that the half-magnetic topological insulator is desirable to realize the surface anomalous Hall effect, which serves as direct proof of the general concept of axion electrodynamics in condensed matter systems.