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Zhiqiang Li, Seminar, May 25, 2016

Published: May 19, 2016

Optical Study of Topological Crystalline Insulators and Graphene/BN Heterostructures



TIME:May 25, 2016

PRESENTER: Zhiqiang Li, Sichuan University

LOCATION: 4F, Building 2

TYPE: Seminar


Abstract:


The surface states of topological crystalline insulators (TCI) arise from the topology of the bulk bands and are protected by crystalline symmetries. So far, the surface states remain mostly elusive in optical and transport experiments. We investigated the infrared (IR) reflectance spectrum of a TCI Pb1-xSnxSe in zero and high magnetic fields. Analysis of the interband Landau level transitions of the TCI phase shows that their bulk bands can be well described by massive Dirac fermions. Moreover, our optical data have revealed several signatures of the surface states in the TCI phase. We will discuss and compare the mobility and DC conductivity of the surface and bulk states. These findings provide new insights in the unique surface states of TCIs.

In the second half of the talk, we report the observation of multiple hot-carrier collection in graphene/boron-nitride Moiré superlattice structures. A record-high zero-bias photoresponsivity of 0.3 A/W (equivalently, an external quantum efficiency exceeding 50%) is achieved using graphene’s photo-Nernst effect, which demonstrates a collection of at least five carriers per absorbed photon. We reveal that this effect arises from the enhanced Nernst coefficient through Lifshtiz transition at low-energy Van Hove singularities, which is an emergent phenomenon due to the formation of Moiré minibands. Our observation points to a new means for extremely efficient and flexible optoelectronics based on van der Waals heterostructures.




Biography:


李志强,四川大学教授,北京大学学士,美国加州大学圣地亚哥分校博士。2015年入选中组部“青年千人计划”,2016年入选四川省“千人计划”。研究领域: 实验凝聚态物理,低维拓扑量子体系的物理及光电子学。发表英文SCI论文34,包括Nature Physics 2篇, Nature Communications 1篇, Science Advances 1, Physical Review Letters 8, Nano Letters 4篇等,论文被引用超过2300次。




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