CM Seminar - Topological valleytronics in bilayer graphene
Abstract : The advent of two-dimensional materials with hexagonal crystal symmetry offers a new electronic degree of freedom, namely valley, the manipulation and detection of which could potentially be exploited to form new many-body ground states as well as new paradigms of electronic applications. In this talk, I will describe how we create valley-momentum locked topological 1D channels, aka quantum valley Hall kink states, in Bernal stacked bilayer graphene by electrically generating inverted band structures. This all-electric construction gives us the ability to realize reconfigurable ballistic waveguides and device operations that explicitly explore the valley-momentum locking of the kink states. I will show the working of a topological valley valve, which does not require valley-polarized current to operate but relies on the control of topology, and a continuously tunable electron beam splitter, which is akin to the function of a quantum point contact for quantum Hall edge states. The high quality and versatile control of the kink states open the door to many exciting fundamental physics inquiries in 1D. Its realization requires the development of high-precision lithography on BN/graphene/BN heterostructures. Time permitting, I will touch upon other works this technique has enabled.
J. Li, K. Wang, K. J. McFaul, Z. Zern, Y. F. Ren, K. Watanabe, T. Taniguchi, Z. H. Qiao, J. Zhu, “Gate-controlled topological conducting channels in bilayer graphene”, Nature Nanotechnology, 11, 1060 (2016)
Jing Li, Rui-Xing Zhang, Zhenxi Yin, Jianxiao Zhang, Kenji Watanabe, Takashi Taniguchi, Chaoxing Liu, Jun Zhu, “A valley valve and electron beam splitter”, Science 362, 1149 (2018)
Biography : Professor Jun Zhu received her PhD from Columbia University in 2003. She was a postdoc fellow in Cornell University from 2003-2005 before joining Penn State University in 2006. She is currently a Professor of Physics at Penn State. Her research interest focuses on the understanding of new physics and device functionalities arising from reduced dimensionality, many-body interactions and the control of new electronic degrees of freedom in nanoscale materials and devices. Her recent research projects explore the electronic properties of van der Waals materials and interferences, with a particular emphasis on valleytronic, topological, and quantum Hall phenomena. Her lab homepage: