Valley subband splitting in bilayer graphene quantum point contact

TL;DR

This study investigates the valley subband splitting in a bilayer graphene quantum point contact, revealing full valley degeneracy lifting at high magnetic fields and valley mixing phenomena, advancing understanding of quantum confinement in graphene.

Contribution

It provides the first detailed observation of valley degeneracy lifting and valley mixing in bilayer graphene quantum point contacts under high magnetic fields.

Findings

Quantized conductance steps of 4e^2/h observed.

Full valley degeneracy lifting at high magnetic fields.

Valley mixing between non-adjacent subbands explained by a semi-phenomenological model.

Abstract

We report a study of one-dimensional subband splitting in a bilayer graphene quantum point contact in which quantized conductance in steps of $4\,e^2/h$ is clearly defined down to the lowest subband. While our source-drain bias spectroscopy measurements reveal an unconventional confinement, we observe a full lifting of the valley degeneracy at high magnetic fields perpendicular to the bilayer graphene plane for the first two lowest subbands where confinement and Coulomb interactions are the strongest and a peculiar merging/mixing of $K$ and $K'$ valleys from two non-adjacent subbands with indices $(N,N+2)$ which are well described by our semi-phenomenological model.