应6163银河net163am安钧鸿教授邀请，湖南大学物理与微电子科学学院童庆军教授来访并做学术报告。欢迎广大师生届时参加！

题目：Novel physics in moiré superlattices of van der Waals heterobilayers

时间：2018年11月15日（周四）下午2：30

地点：格致楼4022

摘要：Van der Waals (vdW) heterostructures formed by two-dimensional atomic crystals provide a powerful approach towards designer condensed matter systems. Incommensurate heterobilayers with small twisting and/or lattice mismatch lead to the interesting concept of moiré superlattices, where the atomic registry is locally indistinguishable from commensurate bilayers but has local-to-local variation over long range.
In this talk, I will show that the moiré superlattices can lead to periodic modulation of local topological order in vdW heterobilayers formed by two massive Dirac materials1. By tuning the vdW heterojunction from normal to the inverted type-II regime via an interlayer bias, the commensurate heterobilayer can become a topological insulator (TI), depending on the interlayer hybridization controlled by the atomic registry between the vdW layers. This results in a mosaic pattern of TI regions and normal insulator (NI) regions in moiré superlattices, where topologically protected helical modes exist at the TI/NI phase boundaries. In van der Waals heterobilayer formed by 2D magnets, I will show a new origin of skyrmions in the 2D magnets, from the lateral modulation of interlayer magnetic coupling by the locally different atomic registries in moiré2. The moiré skyrmions are doubly degenerate with opposite topological charge, and trapped at an ordered array of sites with the moiré periodicity that can be dramatically tuned by strain and interlayer translation. At relatively strong interlayer coupling, the ground states are skyrmion lattices, where magnetic field can switch the skyrmion vorticity and location in the moiré. At weak interlayer coupling limit, we find metastable skyrmion excitations on the ferromagnetic ground state that can be deterministically moved between the ordered moiré trapping sites by current pulses.

个人简介：童庆军，湖南大学物理与微电子科学学院教授。2013年于兰州大学获得理学博士学位，导师是罗洪刚教授和安钧鸿教授。读博期间曾在新加坡国立大学做访问研究助理，合作导师是 Prof. C. H. Oh。2014年8月至2018年9月在香港大学做博士后，合作导师是 Prof. Wang Yao。
研究方向是量子光学和理论凝聚态物理。目前的研究兴趣包括：二维材料和范德瓦尔斯异质结中的自旋能谷现象，平衡以及非平衡量子系统中的拓扑性质，开放系统中的退相干及其抑制。迄今在Nature physics, Nano letters, Phys.Rev.Lett., Phys.Rev.A/B等期刊发表了14篇学术论文。