Abstract：The quantum anomalous Hall effect is a novel topological quantum transport phenomenon that was first   discovered in magnetically doped topological insulator thin films. In recent years, the layered antiferromagnet           topological insulator MnBi2Te4 has emerged as a promising platform for studying quantum anomalous Hall related phenomena. The rich and complex spin dynamics associated with the van der Waals antiferromagnetic order is expected to generate novel topological phases and phase transitions that are unique to MnBi2Te4. The quantum anomalous Hall effect and axion insulator state have been observed in odd- and even-septuple-layer (SL) of MnBi2Te4                respectively. However, it has been a challenging task to fabricate devices that exhibit quantized transport [1], which  hinders the investigation for more exotic topological phases of matter.

In this talk, we present the transport studies of a 7-septuple-layer MnBi2Te4 device covered with AlOx capping  layer, which enables the investigation of antiferromagnetic quantum anomalous Hall effect over wide parameter         spaces. By tuning the gate voltage and perpendicular magnetic field, we uncover a cascade of quantum phase             transitions that can be attributed to the influence of spin configurations on charge transport [2]. Furthermore, we find that an in-plane magnetic field enhances both the coercive field and exchange gap of the surface state, in sharp          contrast to that in ferromagnetic quantum anomalous Hall state. We propose that these peculiar features arise from     the spin flip and flop transitions inherent to van der Waals antiferromagnet. The versatile tunability of the quantum   anomalous Hall effect in MnBi2Te4 paves the way for potential applications in topological antiferromagnetic            spintronics.

References

[1] Y.X. Li et al., Nature Communications 15, 3399 (2024).

[2] Z.C. Lian et al., Nature DOI: 10.1038/s41586-025-08860-z (2025).

专家简介：

    王亚愚，1998年本科毕业于中国科技大学物理系，2004年在美国普林斯顿大学物理系获得博士学位，此后在加州大学伯克利分校任Miller Fellow，2007年12月加入清华大学物理系任教至今。主要从事凝聚态物理实验研究，在量子反常霍尔效应的实验观测、强关联与拓扑系统的量子输运、高温超导体的微观电子结构等领域取得多项系统性研究成果。曾获得中国物理学会“黄昆物理奖”、国家自然科学一等奖（2018年，第二完成人）、首届腾讯“科学探索奖”、入选首届“新基石研究员”项目。