Electrostatically confined monolayer graphene quantum dots with orbital and valley splittings

TL;DR

This paper demonstrates a novel method to create electrostatically confined quantum dots in monolayer graphene using a magnetic field and STM tip, overcoming Klein tunneling and edge disorder issues.

Contribution

It introduces an alternative electrostatic confinement technique in monolayer graphene that does not rely on physical edges or band gap engineering.

Findings

Observed Coulomb peaks with addition energies of 7-20 meV

Detected orbital splittings of 4-10 meV

Measured valley splitting of about 3 meV

Abstract

The electrostatic confinement of massless charge carriers is hampered by Klein tunneling. Circumventing this problem in graphene mainly relies on carving out nanostructures or applying electric displacement fields to open a band gap in bilayer graphene. So far, these approaches suffer from edge disorder or insufficiently controlled localization of electrons. Here we realize an alternative strategy in monolayer graphene, by combining a homogeneous magnetic field and electrostatic confinement. Using the tip of a scanning tunneling microscope, we induce a confining potential in the Landau gaps of bulk graphene without the need for physical edges. Gating the localized states towards the Fermi energy leads to regular charging sequences with more than 40 Coulomb peaks exhibiting typical addition energies of 7-20 meV. Orbital splittings of 4-10 meV and a valley splitting of about 3 meV for the first orbital state can be deduced. These experimental observations are quantitatively reproduced by tight binding calculations, which include the interactions of the graphene with the aligned hexagonal boron nitride substrate. The demonstrated confinement approach appears suitable to create quantum dots with well-defined wave function properties beyond the reach of traditional techniques.