Dirac-fermion approach and unexpected gapless surface states of layered magnetic topological insulators

报告题目:Dirac-fermion approach and unexpected gapless surface states of layered magnetic topological insulators

报告人:张海军教授  南京大学

报告时间:2022 12 20日下午 15:30-16:30

报告地点:腾讯会议460-813-754

报告摘要:The recently discovered MnBi2Te4-family magnetic topological insulators (TIs), have aroused great attention, where the interlayer vdW gap is expected to play a crucial role in their topological states. It remains a controversy whether the surface states are gapped or gapless for antiferromagnetic TI MnBi2Te4, and how to understand this controversy is still challenge. In this talk, we first introduce a Dirac-fermion approach to generally describe surface states of layered vdW TIs. In particular, we apply this approach to the surface state of layered antiferromagnetic TI MnBi2Te4. Remarkably, unexpected topologically protected gapless surface states are found to arise under a slight surface vdW gap expansion (~0.2 A), if the surface ferromagnetic layer has a zero Chern number; while the surface states remain gapped for other cases. The unexpected gapless topological states provide a unique intrinsic mechanism to understand the puzzle of the observed surface states of MnBi2Te4. This work also provides a promising way for experiments to realize higher-temperature quantum anomalous Hall effect in MnBi2Te4.

报告人简介:张海军,2004年于中国科学技术大学获得物理学学士学位;2009年于中国科学院物理研究所获得理学博士学位;2010年开始在美国Stanford大学从事博士后研究,2015年加入南京大学,任教授。主要从事计算凝聚态物理方面的前沿基础研究,探索和理解凝聚态物理中的各种新奇物性,在拓扑量子材料探索和拓扑物性研究方面取得了一些具有国际影响力的原创性研究成果。已发表了90余篇论文,总引用超过17300次。获聘教育部长江学者特聘教授(2020);获得香港求是科学基金会‘求是杰出科技成就奖集体奖’(2011)等。

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