Realization of the quantum anomalous Hall effect and axion electrodynamics in topological materials are among the paradigmatic phenomena in condensed matter physics. Recently, signatures of both phases are observed to exist in thin films of MnBi2Te4, a stoichiometric antiferromagnetic topological insulator. Direct evidence of the bulk topological magnetoelectric response in an axion insulator requires an energy gap at its topological surface state (TSS). However, independent spectroscopic experiments revealed that such a surface gap is absent, or much smaller than previously thought, in MnBi2Te4. Here, we utilize angle resolved photoemission spectroscopy and density functional theory calculations to demonstrate that a sizable TSS gap unexpectedly exists in Sb-doped MnBi2Te4. This gap is found to be topologically nontrivial, insensitive to the bulk antiferromagnetic-paramagnetic transition, while enlarges along with increasing Sb concentration. Our work shows that Mn(Bi1−xSbx)2Te4 is a potential platform to observe the key features of the high-temperature axion insulator state, such as the topological magnetoelectric responses and half-integer quantum Hall effects.
@article{arxiv.2004.09123,
title = {Spectroscopic realization of large surface gap in a doped magnetic topological insulator},
author = {Xiao-Ming Ma and Yufei Zhao and Ke Zhang and Rui'e Lu and Jiayu Li and Qiushi Yao and Jifeng Shao and Xuefeng Wu and Meng Zeng and Yu-Jie Hao and Shiv Kumar and Zhanyang Hao and Yuan Wang and Xiang-Rui Liu and Huiwen Shen and Hongyi Sun and Jiawei Mei and Koji Miyamoto and Taichi Okuda and Masashi Arita and Eike F. Schwier and Kenya Shimada and Ke Deng and Cai Liu and Yue Zhao and Chaoyu Chen and Qihang Liu and Chang Liu},
journal= {arXiv preprint arXiv:2004.09123},
year = {2021}
}