Scanning gate microscopy of localized states in a gate-defined bilayer graphene channel

Carolin Gold,Klaus Ensslin,Takashi Taniguchi,Thomas Ihn,Annika Kurzmann,Kenji Watanabe

doi:10.1103/physrevresearch.2.043380

Carolin Gold, Klaus Ensslin + Show 4 more

Open Access

https://doi.org/10.1103/physrevresearch.2.043380

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Abstract

We use Scanning Gate Microscopy to demonstrate the presence of localized states arising from potential inhomogeneities in a 50nm-wide, gate-defined conducting channel in encapsulated bilayer graphene. When imaging the channel conductance under the influence of a local tip-induced potential, we observe ellipses of enhanced conductance as a function of the tip position. These ellipses allow us to infer the location of the localized states and to study their dependence on the displacement field. For large displacement fields, we observe that localized states tend to occur halfway into the channel. All our observations can be well explained within the framework of stochastic Coulomb blockade.

Highlights

Graphene is a promising material for semiconducting quantum-dot-based qubits due to its small spin-orbit coupling and small hyperfine interaction [1]
We presented scanning gate measurements on a gatedefined channel in high-quality bilayer graphene
The scanning gate images reveal the occurrence of stochastic Coulomb blockade in the conductance through the channel at various displacement fields

Summary

INTRODUCTION

Graphene is a promising material for semiconducting quantum-dot-based qubits due to its small spin-orbit coupling and small hyperfine interaction [1]. If the latter condition is met, their smooth edge potentials in comparison to the previously etched devices minimize the appearance of localized edge states This made it possible to prepare high-quality quantum point contacts [8,12] as well as few-electron or few-hole quantum dots in bilayer-graphene channels [13,14]. Scanning the voltagebiased metallic tip of an atomic force microscope over the channel perturbs the potential landscape locally This technique has previously been used to image localized states, both disorder induced as well as engineered, in systems as diverse as InAs nanowires [20], GaAs heterostructures [21,22], carbon nanotubes [23,24,25,26], and graphene [27,28,29]. Insights into the evolution of the localized states as a function of the band-gap size and electron concentration

SAMPLE CHARACTERIZATION

TIP INFLUENCE ON THE CONDUCTANCE RESONANCES

CONCLUSION