Experimental realization of gate controlled topological conducting channels in bilayer graphene

Manipulating the valley degree of freedom in two-dimensional honeycomb lattices can potentially lead to a new type of electronics called valleytronics. In electrically gapped bilayer graphene, the broken inversion symmetry leads to non-zero and asymmetric Berry curvature $\Omega$ in the K and K$^\prime$ valleys of the Brillouin zone. Reversing the sign of $\Omega$ at the internal line junction of two oppositely gated bilayer graphene is predicted to yield counter-propagating edge modes, the so-called kink states, with quantized conductance of $4e^2/h$ in the absence of valley mixing. We have overcome fabrication challenges to implement high-quality hBN encapsulated, dual-split-gates structures necessary to observe the kink states. Here I present experimental evidences of the kink states. In the absence of a magnetic field, the kink states have a mean free path of a few hundred nm. Ballistic conductance of $4e^2/h$ is achieved in a perpendicular magnetic field. We discuss the potential valley-mixing mechanisms and the role of the magnetic field. Experimental results are supported by numerical studies. We will also discuss ongoing efforts in realizing valley-controlled transmission and guiding of the kink states, which is a significant step towards the development of valleytronics.