本学期第3次午餐会邀请南京大学物理学院杜灵杰教授做学术报告。 

报告题目：Two dimensional topological phenomena in semiconductor artificial structures: from quantum spin Hall effect to artificial graphene

报告人：杜灵杰 教授，南京大学 物理学院

报告时间：10月22日 中午12：00

报告地点：南京大学鼓楼校区唐仲英楼B501

报告摘要：Two-dimensional (2D) topological effects that interplay with electron-electron interactions have attracted lots of attention in the field of condensed matter physics. Quantum spin Hall (QSH) effect is such a typical topological effect. In this talk fist I will present recent experimental studies of QSH effect in inverted InAs/GaSb quantum wells (QWs). In inverted InAs/GaSb QWs, using charge-neutral point (CNP) density as a tuning parameter, we observed that a spontaneous excitonic gap opens in the bulk, with the emergence of time-reversal-symmetry (TRS)-broken QSH effect where helical edges persist under high magnetic fields. To clarify the interesting observation, we performed transport and THz measurements, and observed evidence for long-sought-after 2D excitonic insulator (EI). Then I will present recent progresses of semiconductor artificial graphene (AG) in nanopatterned GaAs QWs, which would offer exclusive tunability to 2D topological effects. In semiconductor AG, through resonant inelastic light scattering we observed linearly dispersing Dirac bands. After triangular antidots geometry was introduced, the processing disorder in AG was strongly suppressed where electron-electron interaction effects become prominent. In the low-disorder AG, we observed THz spin exciton modes, which have very large exchange energies that are comparable with excitonic energies. Then I will discuss recent experimental results in flat bands of the low-disorder AG. The interplay between geometric and topological effects not only exists in AG, but also emerges in fractional quantum Hall(FQH) effects. We observed unexpected collective modes in the FQH regime: intra-Landau-level plasmons, which supports the proposed model of a FQH nematic state. Other explanation such as FQH graviton will be discussed.

报告人简介：杜灵杰，南京大学物理学院教授、博士生导师。 2008年南京大学理科强化部获得物理学学士学位，2011年南京大学物理学院获得物理学硕士学位，2016年美国莱斯大学获得物理学博士学位，2016-2019年在美国哥伦比亚大学从事博士后研究工作，2019年入选中组部国家“千人计划”青年项目，同年全职回南京大学工作。目前主要研究方向：以半导体电子器件为基础，通过电学和光学的综合测量手段在极低温下研究电子的新型凝聚态和新型拓扑态。

欢迎各位老师参加。

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                       江苏省物理学会青年工作委员会

                                     2019年10月21日