Transport through graphene quantum dots

Abstract

We review transport experiments on graphene quantum dots and narrow graphene constrictions. In a quantum dot, electrons are confined in all lateral dimensions, offering the possibility for detailed investigation and controlled manipulation of individual quantum systems. The recently isolated two-dimensional carbon allotrope graphene is an interesting host to study quantum phenomena, due to its novel electronic properties and the expected weak interaction of the electron spin with the material. Graphene quantum dots are fabricated by etching mono-layer flakes into small islands (diameter 60-350 nm) with narrow connections to contacts (width 20-75 nm), serving as tunneling barriers for transport spectroscopy. Electron confinement in graphene quantum dots is observed by measuring Coulomb blockade and transport through excited states, a manifestation of quantum confinement. Measurements in a magnetic field perpendicular to the sample plane allowed to identify the regime with only a few charge carriers in the dot (electron-hole transition), and the crossover to the formation of the graphene specific zero-energy Landau level at high fields. After rotation of the sample into parallel magnetic field orientation, Zeeman spin splitting with a g-factor of g ≈ 2 is measured. The filling sequence of subsequent spin states is similar to what was found in GaAs and related to the non-negligible influence of exchange interactions among the electrons.

Epitaxial graphene quantum dots for high-performance terahertz bolometers

“…The black (red) circles correspond to dots with steps perpendicular (parallel) to the direction of the current flow. The activation energies are roughly proportional to the inverse of the dot diameter.This is consistent with quantum dots from exfoliated graphene 13,14 , where the combination of the charging energy and the confinement energy open a bandgap that is inversely proportional to the dot diameter. Another notable feature in Fig.…”

Measurements of the transport gap in semiconducting multiwalled carbon nanotubes with varying diameter and length

“…GNRs always exhibit a transport gap as the width of them is reduced down to the range of a few or a few tens of nanometers [48,52,53], possibly with the exception for some very recent papers [22]. This is in contrast to the MWNTs of this paper, which also include metallic transport at all diameters, and of course, it has been known since the early days of carbon nanotube research that SWNTs can be both metallic and semiconducting conductors, although, according to Ref.…”

Formation mechanism of bound states in graphene point contacts

“…Nanostructures made of graphene can be patterned using lithography technique [15]. Graphene QPCs have been fabricated and extensively studied [16][17][18][19][20][21][22][23]. A shortest-possible QPC, which is made of a single hexagon and makes an aperture for electrons, has been theoretically examined [22], and typical wave diffraction patterns were predicted.…”