Condensed Matter Seminar - "The 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 quantization is robust down to milliKelvin and up to tens of Kelvin. The all-electrical construction of the kink states gives us the ability to realize a variety of electron quantum optics operations.

I will show the workings of a reconfigurable ballistic waveguide, a topological valley valve, and a continuously tunable electron beam splitter. The cleanness and controllability of the kink states enable future experiments exploring the fundamental properties of helical edge states and their potential use as quantum interconnects.

1-3 Li, J. et al. Gate-controlled topological conducting channels in bilayer graphene. Nature Nanotechnology 11, 1060, doi:10.1038/Nnano.2016.158 (2016).Li, J. et al. A valley valve and electron beam splitter.

Science 362, 1149, doi:10.1126/science.aao5989 (2018).Huang, K., Fu, H., Watanabe, K., Taniguchi, T. & Zhu, J. High-temperature quantum valley Hall effect with quantized resistance and a topological switch.

Science 385, 657, doi:10.1126/science.adj3742 (2024).