Electrostatically induced quantum point contact in bilayer graphene

TL;DR

This paper demonstrates the fabrication of high-resistance electrostatically defined nanostructures in bilayer graphene, revealing conductance quantization and Landau level degeneracy, advancing quantum device engineering.

Contribution

It introduces a method using a graphite back gate to create nanostructures in bilayer graphene with unprecedented high resistance and observes quantized conductance and Landau levels.

Findings

Leakage resistance exceeds 10 GΩ, surpassing previous values.

Observation of conductance quantization at 2e^2/h and 4e^2/h.

Recovery of four-fold Landau level degeneracy in magnetic fields.

Abstract

We report the fabrication of electrostatically defined nanostructures in encapsulated bilayer graphene, with leakage resistances below depletion gates as high as $R \sim 10~$G$\Omega$. This exceeds previously reported values of $R =~$10 - 100 k$\Omega$.\cite{Zou2010,Yan2010,Zhu2016a} We attribute this improvement to the use of a graphite back gate. We realize two split gate devices which define an electronic channel on the scale of the Fermi-wavelength. A channel gate covering the gap between the split gates varies the charge carrier density in the channel. We observe device-dependent conductance quantization of $\Delta G = 2~e^2/h$ and $\Delta G = 4~e^2/h$. In quantizing magnetic fields normal to the sample plane, we recover the four- fold Landau level degeneracy of bilayer graphene. Unexpected mode crossings appear at the crossover between zero magnetic field and the quantum Hall regime.