Valley polarized conductance quantization in bilayer graphene narrow quantum point contact

Abstract

In this study, we fabricated quantum point contacts narrower than 100 nm by using an electrostatic potential to open the finite bandgap by applying a perpendicular electric field to bilayer graphene encapsulated between hexagonal boron nitride sheets. The conductance across the quantum point contact was quantized at a high perpendicular-displacement field as high as 1 V/nm at low temperature, and the quantization unit was 2e2/h instead of mixed spin and valley degeneracy of 4e2/h. This lifted degeneracy state in the quantum point contact indicates the presence of valley polarized state coming from potential profile or effective displacement field in one-dimensional channel.