Signatures of single quantum dots in graphene nanoribbons within the quantum Hall regime.

Endre Tóvári,Peter Rickhaus,Péter Makk,Christian Schönenberger,Szabolcs Csonka

doi:10.1039/c6nr00187d

Abstract

We report on the observation of periodic conductance oscillations near quantum Hall plateaus in suspended graphene nanoribbons. They are attributed to single quantum dots that are formed in the narrowest part of the ribbon, in the valleys and hills of a disorder potential. In a wide flake with two gates, a double-dot system's signature has been observed. Electrostatic confinement is enabled in single-layer graphene due to the gaps that are formed between the Landau levels, suggesting a way to create gate-defined quantum dots that can be accessed with quantum Hall edge states.

Highlights

The high mobility of graphene offers a good platform for field effect transistors, whereas the low spin–orbit coupling[5] and small amount of 13C nuclear spins make it promising for the realization of long-lifetime spin qubits.[6,7,8,9]
From an application point of view, the absence of a band gap places limitations: it hinders effective electrostatic confinement of electrons, which makes the fabrication of spin qubits challenging and results in high OFF state currents for field effect transistors
The common technique to confine electrons in a graphene quantum dot (QD) or ribbon is based on tailoring the graphene sheet by etching

Summary

Introduction

The Dirac spectrum results in several peculiar features in the charge transport of graphene, such as Klein tunneling, or the special Berry phase and the half-integer quantum Halleffect.[1,2,3,4] The high mobility of graphene offers a good platform for field effect transistors, whereas the low spin–orbit coupling[5] and small amount of 13C nuclear spins make it promising for the realization of long-lifetime spin qubits.[6,7,8,9] from an application point of view, the absence of a band gap places limitations: it hinders effective electrostatic confinement of electrons, which makes the fabrication of spin qubits challenging and results in high OFF state currents for field effect transistors. Other confinement strategies involve opening a gap in bilayer graphene using perpendicular electric fields, or exploiting the angle-dependent transmission in p–n junctions. Both techniques require ultra-clean high mobility junctions, for which encapsulation in hBN24,25 or suspension of the graphene flake[26,27] is required. Quantum dots and point contacts have been created by utilizing the gap opening in bilayer graphene.[28,29,30] beamsplitters and waveguides were fabricated using p–n junctions,[31,32] the confinement offered by the p–n transition is imperfect and electrons can leak out. Our findings show a proof of principle that the B-field induced Landau gap and a local electric field can be used to confine charges to quantum dots

Results and discussion

Conclusions

Methods