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Seminar: Optical Study of Graphene Heterostructures and Topological Materials

 Zhiqiang Li

College of Physical Science and Technology, Sichuan University 

Time: 4:00-5:00pm, Monday, Oct. 29th, 2018

Location: Room 242, East-4, Zijingang Campus


Abstract:

 
Many new quantum phenomena have been observed in graphene heterostructures recently, which have attracted great interest. In this talk, we will present photocurrent study of graphene/BN heterostructures in magnetic field. A record-high zero-bias photoresponsivity of 0.3 A/W is achieved using graphene’s photo-Nernst effect, which demonstrates a collection of at least five carriers per absorbed photon. We show that this effect arises from the enhanced Nernst coefficient through Lifshtiz transition at low-energy Van Hove singularities. This observation points to a new means for efficient and flexible optoelectronics based on van der Waals heterostructures.

In many topological materials, it remains a challenge to probe optical and transport properties of the topological surface states. We will report our infrared study of a topological crystalline insulator (TCI) Pb0.7Sn0.3Se. We demonstrate that the far-infrared conductivity is dominated by the surface states as a result of their unique band structure and the consequent high surface carrier density. Moreover, our experiments yield a surface mobility of 40,000 cm2 V-1 s-1, which suggests the viability of surface-dominated conduction in thin TCI crystals. These findings open up new opportunities for exploring the exotic physics predicted for TCIs. We will also report cyclotron resonance study of SmB6, a candidate for topological Kondo insulator. Features associated with surface states of this material will be analyzed and discussed.


About the Speaker:

 
Dr. Zhiqiang Li (李志强) obtained his B.S. degree from Peking University in 2002 and Ph.D. from University of California at San Diego in 2008. After being a postdoc researcher at Columbia University (2008-2011) and research faculty at the National High Magnetic Field Lab. (2011-2015), he joined the college of Physical Science and Technology at Sichuan University as a full professor in 2015. Dr. Li’s research interests include experimental studies on the optical and electronic properties of low-dimensional systems and topological materials, such as graphene and other novel 2D materials, topological insulators, etc. He is also a fellow of the national youth thousand talents and Sichuan thousand talents.