MnBi2Te4 is an antiferromagnetic topological insulator which stimulates intense interests due to the exotic quantum phenomena and promising device applications. Surface structure is a determinant factor to understand the novel magnetic and topological behavior of MnBi2Te4, yet its precise atomic structure remains elusive. Here, we discovered a spontaneous surface collapse and reconstruction in few-layer MnBi2Te4 exfoliated under delicate protection. Instead of the ideal septuple-layer structure in the bulk, the collapsed surface is shown to reconstruct as Mn-doped Bi2Te3 quintuple-layer and MnxBiyTe double-layer with a clear van der Waals gap in between. Combining with first-principles calculations, such spontaneous surface collapse is attributed to the abundant intrinsic Mn-Bi antisite defects and tellurium vacancy in the exfoliated surface, which is further supported by in-situ annealing and electron irradiation experiments. Our results shed light on the understanding of the intricate surface-bulk correspondence of MnBi2Te4, and provide insightful perspective of the surface-related quantum measurements in MnBi2Te4 few-layer devices.
@article{arxiv.2004.08138,
title = {Spontaneous Surface Collapse and Reconstruction in Antiferromagnetic Topological Insulator MnBi$_2$Te$_4$},
author = {Fuchen Hou and Qiushi Yao and Chun-Sheng Zhou and Xiao-Ming Ma and Mengjiao Han and Yu-Jie Hao and Xuefeng Wu and Yu Zhang and Hongyi Sun and Chang Liu and Yue Zhao and Qihang Liu and Junhao Lin},
journal= {arXiv preprint arXiv:2004.08138},
year = {2020}
}