title: Size quantization of Dirac fermions in graphene constrictions.
abstract: Quantum point contacts are cornerstones of mesoscopic physics and central building blocks for quantum electronics. Although the Fermi wavelength in high-quality bulk graphene can be tuned up to hundreds of nanometres, the observation of quantum confinement of Dirac electrons in nanostructured graphene has proven surprisingly challenging. Here we show ballistic transport and quantized conductance of size-confined Dirac fermions in lithographically defined graphene constrictions. At high carrier densities, the observed conductance agrees excellently with the Landauer theory of ballistic transport without any adjustable parameter. Experimental data and simulations for the evolution of the conductance with magnetic field unambiguously confirm the identification of size quantization in the constriction. Close to the charge neutrality point, bias voltage spectroscopy reveals a renormalized Fermi velocity of ∼1.5 × 10(6) m s(-1) in our constrictions. Moreover, at low carrier density transport measurements allow probing the density of localized states at edges, thus offering a unique handle on edge physics in graphene devices.
authors.affiliation: JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52056 Aachen, Germany.|Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Terrés
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, 1040 Vienna, Austria.
authors.forename: L A
authors.initials: LA
authors.lastname: Chizhova
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, 1040 Vienna, Austria.
authors.forename: F
authors.identifier: 0000-0001-5641-9458
authors.initials: F
authors.lastname: Libisch
authors.affiliation: JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52056 Aachen, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Peiro
authors.affiliation: JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52056 Aachen, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Jörger
authors.affiliation: JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52056 Aachen, Germany.|Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Engels
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, 1040 Vienna, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Girschik
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: K
authors.identifier: 0000-0003-3701-8119
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52056 Aachen, Germany.|Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015, USA.|Center for Advanced Materials and Nanotechnology, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
authors.forename: S V
authors.initials: SV
authors.lastname: Rotkin
authors.affiliation: Institute for Theoretical Physics, Vienna University of Technology, 1040 Vienna, Austria.|Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), 4001 Debrecen, Hungary.
authors.forename: J
authors.initials: J
authors.lastname: Burgdörfer
authors.affiliation: JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52056 Aachen, Germany.|Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Stampfer