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 with natural heterostructure is an unprecedented “half-magnetic topological insulator,” with the magnetization existing at the surface but not at the opposite surface terminated by triple layers. Our angle-resolved photoemission spectroscopy measurements unveil a massive Dirac gap at the surface and a gapless Dirac cone on the other side. Remarkably, the Dirac gap (about 28 meV) at the surface decreases monotonically with increasing temperature and closes right at the Curie temperature, thereby representing the first smoking-gun spectroscopic evidence of a 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 surface anomalous Hall effect, which serves as direct proof of the general concept of axion electrodynamics in condensed matter systems.
- Received 9 September 2020
- Revised 17 November 2020
- Accepted 13 January 2021
DOI:https://doi.org/10.1103/PhysRevX.11.011039
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Erratum
Erratum: Half-Magnetic Topological Insulator with Magnetization-Induced Dirac Gap at a Selected Surface [Phys. Rev. X 11, 011039 (2021)]
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, Jiawei Mei, Yue Zhao, Cai Liu, Ke Deng, Wen Huang, Bing Shen, Kenya Shimada, Eike F. Schwier, Chang Liu, Qihang Liu, and Chaoyu Chen
Phys. Rev. X 11, 029902 (2021)
Popular Summary
Topological insulators (TIs) support the flow of electric currents only on their surfaces but not in their interiors. Ordered magnetic elements generally destroy the surface conductivity of the TIs, making them insulating throughout. However, such magnetic TIs are promised to host two exotic quantum phenomena: the quantum anomalous Hall effect and the axion insulating state. Partially because of the lack of suitable materials, thus far it is not clear if the latter case can be observed. In this work, we find experimentally that an intrinsic ferromagnetic TI can be an ideal platform for exploring the key signature of axion dynamics.
Specifically, we find that these materials are excellent for studying and manipulating exotic half-quantized surface conductance, in which the electrical conductance at the surface takes on a very particular set of discrete values. Using angle-resolved photoemission, we reveal that the conducting surfaces of a specific ferromagnetic TI become insulating at low temperatures but return to normal TI behavior at exactly the transition temperature where its ferromagnetism is killed. This phenomenon happens only at its magnetic layer but not at its nonmagnetic layers. We further demonstrate theoretically that this system can be termed a “half-magnetic topological insulator,” possessing a half-quantized surface anomalous transverse (or Hall) conductivity.
Our result calls for direct measurements of such half-quantized Hall currents in this system, which would be a direct proof of the general concept of axion electrodynamics in condensed matter systems.