Conventional CMOS field effect transistors control current transmission by controlling the charge of carriers. The advent of two-dimensional materials with hexagonal crystal symmetry offers a new electronic degree of freedom, namely valley, the manipulation of which could potentially be exploited to form new many-body ground states as well as new paradigms of electronic applications.  We demonstrated the experimental evidence of the quantum valley Hall effect and its precise resistance quantization at zero magnetic field at the line junction of oppositely gated bilayer graphene regions. The quantization is robust up to several tens of Kelvin and tens of mV in dc bias. We further demonstrate a topological phase transition controlled switch,  gate-controlled transmission of the kink states at a four-way junction. The operations of a valley valve, waveguide and tunable beam splitter are realized. They are examples of valleytronic operations and exploit the topological and helical nature of the kink states. To perform these experiments, we developed precision lithographic techniques to fabricate aligned top and bottom local gates on BN encapsulated bilayer graphene structures. The high quality and versatility of the system opens the door to many exciting opportunities in exploring many-electron physics in one dimension and using the kink states as quantum interconnects.

Publications:

Jun's public lecture as part of the Ashtekar Frontiers Science Lecture Series, March 1, 2025

Press release on Ke's work published in 2024: https://www.psu.edu/news/research/story/kink-state-control-may-provide-pathway-quantum-electronics

K. Huang, H. Fu, K. Watanabe, T. Taniguchi, J. Zhu, "High-temperature quantum valley Hall effect with quantized  resistance and a topological switch", Science  385, 657-661 (2024) 

See press release of Penn State: "Kink state control may provide pathway to quantum electronics".

J. Li, R. Zhang, Z. Yin, J. Zhang, K. Watanabe, T. Taniguchi, C. Liu, J. Zhu, “A valley valve and electron beam splitter", Science 362, 1149 (2018)

See press release of MRI: “New Traffic Rules in 'Graphene City'”.

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 Nanotechnol.  11, 1060 (2016)

See press release at Science Daily: A device to control 'color' of electrons in graphene provides path to future electronics.

See Jun's Penn State 2DCC webinar "Topological valleytronics in bilayer graphene" on Nov 7, 2017