Valley-symmetric quantized conductance in bilayer graphene constrictions

Electrical transport across top-gated short constrictions of bilayer graphene is investigated. Realizing a quasi-one-dimensional (quasi-1D) channel along a physically tailored graphene layer turns out to be extremely challenging due to scattering by the edge disorder and charged puddles. In this study, to obtain the ballistic quasi-1D channel by minimizing the edge scattering in bilayer graphene, we prepared short constrictions of bilayer graphene encapsulated between a pair of crystalline hexagonal boron nitride (hBN) flakes. At high charge carrier densities, lateral confinement of charge carriers in the short constriction (~200 nm wide and ~50 nm long) of hBN-encapsulated bilayer graphene leads to the formation of quasi-1D channels, showing the quantized conductance in steps of ~4e²/h for varying the Fermi wavelength. This signifies that both spin and valley degeneracies are preserved for the carrier transport through the short constriction. We study the evolution of quantized conductance with varying parameters such as magnetic field, temperature, and bias voltage.