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 南京大学物理学院

报告时间： 2022.11.25（星期五）   14：30-15：30

报告地点：腾讯会议ID: 665-461-811

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 topological surface states. However, it remains a serious controversy whether the surface states are gapped or gapless for magnetic TI MnBi2Te4, which is a crucial issue for the prospect of various magnetic topological states. In this talk, we introduce a Dirac-fermion approach to generally describe surface states of layered nonmagnetic/magnetic vdW TIs under the interlayer vdW gap modulation. In particular, we apply this approach to the surface states of vdW antiferromagnetic TIs. Remarkably, unexpected topologically protected gapless Dirac-cone surface states are found to arise under a slight surface vdW gap expansion, if the surface ferromagnetic layer has a zero Chern number, while the surface states remain gapped for all other cases. The unexpected gapless Dirac-cone states are invaluable in solving the puzzle of the observed gapless surface states in MnBi2Te4. This work provides a promising way for experiments to realize intrinsic magnetic quantum anomalous Hall effect with a large energy gap.

报告人简介：

张海军，南京大学物理学院教授，博士生导师，长江学者特聘教授。2011年获得香港求是科学基金会“求是杰出科技成就奖集体奖”。2015年入选“国家海外高层次人才引进计划”（青年项目）。2020年入选教育部“长江学者奖励计划”特聘教授。长期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，特别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。譬如，发现了一系列代表性的拓扑量子体系（迄今最重要的Bi2Se3类拓扑绝缘体、本征磁性的轴子绝缘体MnBi2Te4，二维材料拓扑超导2M-WS2）；原创性提出了一系列的拓扑物性数值计算方法（基于最局域Wannier函数）等。目前发表SCI学术论文80余篇，包括Science3篇，Nature子刊/PRL 30篇等，论文总引用超过17300次。