title: Electrostatically Confined Monolayer Graphene Quantum Dots with Orbital and Valley Splittings.
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 toward 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.
authors.affiliation: II. Institute of Physics B and JARA-FIT, RWTH Aachen University , Otto-Blumenthal-Straße, 52074 Aachen, Germany.
authors.forename: Nils M
authors.initials: NM
authors.lastname: Freitag
authors.affiliation: Institute for Theoretical Physics, TU Wien , Wiedner Hauptstraße 8-10, 1040 Vienna, Austria, EU.
authors.forename: Larisa A
authors.initials: LA
authors.lastname: Chizhova
authors.affiliation: II. Institute of Physics B and JARA-FIT, RWTH Aachen University , Otto-Blumenthal-Straße, 52074 Aachen, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Nemes-Incze
authors.affiliation: School of Physics and Astronomy, University of Manchester , Manchester M13 9PL, United Kingdom.
authors.forename: Colin R
authors.initials: CR
authors.lastname: Woods
authors.affiliation: School of Physics and Astronomy, University of Manchester , Manchester M13 9PL, United Kingdom.
authors.forename: Roman V
authors.initials: RV
authors.lastname: Gorbachev
authors.affiliation: School of Physics and Astronomy, University of Manchester , Manchester M13 9PL, United Kingdom.
authors.forename: Yang
authors.initials: Y
authors.lastname: Cao
authors.affiliation: School of Physics and Astronomy, University of Manchester , Manchester M13 9PL, United Kingdom.
authors.forename: Andre K
authors.initials: AK
authors.lastname: Geim
authors.affiliation: School of Physics and Astronomy, University of Manchester , Manchester M13 9PL, United Kingdom.
authors.forename: Kostya S
authors.initials: KS
authors.lastname: Novoselov
authors.affiliation: Institute for Theoretical Physics, TU Wien , Wiedner Hauptstraße 8-10, 1040 Vienna, Austria, EU.
authors.forename: Joachim
authors.initials: J
authors.lastname: Burgdörfer
authors.affiliation: Institute for Theoretical Physics, TU Wien , Wiedner Hauptstraße 8-10, 1040 Vienna, Austria, EU.
authors.forename: Florian
authors.initials: F
authors.lastname: Libisch
authors.affiliation: II. Institute of Physics B and JARA-FIT, RWTH Aachen University , Otto-Blumenthal-Straße, 52074 Aachen, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Morgenstern
keywords: Graphene; Landau quantization; STM; orbital splitting; quantum dot; valley splitting