High-Temperature Quantum Valley Hall Effect and Topological Valleytronics

One-dimensional edge states arising from a system of non-trivial bulk topology are potential quantum information carriers and platforms to explore the physics of topology and interactions. In this talk, I will discuss our effort in realizing the quantum valley Hall effect and the properties of its edge state, the kink states. Using van der Waals stacking and precision lithography, we create valley-momentum locked kink states in bilayer graphene and demonstrate its precise resistance quantization, a hallmark of ballistic edge state transport. The resistance quantization remains very robust against temperature, only changing by about 3% at ~ 50 K. The all-electrical construction of the kink states gives us the ability to realize a number of valleytronics operations. I will show the workings of a switch drive by topological phase transitions, reconfigurable ballistic waveguides, a topological valley valve, and a continuously tunable electron beam splitter. The cleanness and maneuverability of this platform enables future experiments of edge state physics and bolds well for its potential application as quantum information highways.

In collaboratin with:
Ke Huang, Jing Li, Hailong Fu, Rui-xing Zhang, Zhenxi Yin, K. J. McFaul, Z. Zern, Jianxiao Zhang, Chaoxing Liu, Penn State University
K. Wang, Y. F. Ren, Zhenhua Qiao, University of Science and Technology of China, China
K. Watanabe and T. Taniguchi, The National Instiitute of Materials Science, Japan
References
[1] 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)
[2] 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)
[3] Ke Huang, Hailong Fu, Kenji Watanabe, Takashi Taniguchi, Jun Zhu, “ High-Temperature Quantum Valley Hall Effect with Quantized Resistance and a Topological Switch”, Science, 385, 657 (2024)