1,924 research outputs found
Third edge for a graphene nanoribbon: A tight-binding model calculation
The electronic and transport properties of an extended linear defect embedded
in a zigzag nanoribbon of realistic width are studied, within a tight binding
model approach. Our results suggest that such defect profoundly modify the
properties of the nanoribbon, introducing new conductance quantization values
and modifying the conductance quantization thresholds. The linear defect along
the nanoribbon behaves as an effective third edge of the system, which shows a
metallic behavior, giving rise to new conduction pathways that could be used in
nanoscale circuitry as a quantum wire.Comment: 6 pages, 6 figures. Two new figures and a few references adde
Emergence of magnetism in graphene materials and nanostructures
Magnetic materials and nanostructures based on carbon offer unique
opportunities for future technological applications such as spintronics. This
article reviews graphene-derived systems in which magnetic correlations emerge
as a result of reduced dimensions, disorder and other possible scenarios. In
particular, zero-dimensional graphene nanofragments, one-dimensional graphene
nanoribbons, and defect-induced magnetism in graphene and graphite are covered.
Possible physical mechanisms of the emergence of magnetism in these systems are
illustrated with the help of computational examples based on simple model
Hamiltonians. In addition, this review covers spin transport properties,
proposed designs of graphene-based spintronic devices, magnetic ordering at
finite temperatures as well as the most recent experimental achievements.Comment: tutorial-style review article -- 18 pages, 19 figure
Conductance quantization and transport gap in disordered graphene nanoribbons
We study numerically the effects of edge and bulk disorder on the conductance
of graphene nanoribbons. We compute the conductance suppression due to
localization induced by edge scattering. We find that even for weak edge
roughness, conductance steps are suppressed and transport gaps appear. These
gaps are approximately inversely proportional to the nanoribbon width. On/off
conductance ratios grow exponentially with the nanoribbon length. Our results
impose severe limitations to the use of graphene in ballistic nanowires.Comment: 5 pages, 7 figures; references added, typos fixed, to appear in Phys.
Rev
Effect of disorder with long-range correlation on transport in graphene nanoribbon
Transport in disordered armchair graphene nanoribbons (AGR) with long-range
correlation between quantum wire contact is investigated by transfer matrix
combined with Landauer's formula. Metal-insulator transition is induced by
disorder in neutral AGR. Thereinto, the conductance is one conductance quantum
for metallic phase and exponentially decays otherwise when the length of AGR is
infinity and far longer than its width. Similar to the case of long-range
disorder, the conductance of neutral AGR first increases and then decreases
while the conductance of doped AGR monotonically decreases, as the disorder
strength increases. In the presence of strong disorder, the conductivity
depends monotonically and non-monotonically on the aspect ratio for heavily
doped and slightly doped AGR respectively.Comment: 6 pages, 8 figures; J. Phys: Condensed Matter (May 2012
Transport through graphene nanoribbons: suppression of transverse quantization by symmetry breaking
We investigate transport through nanoribbons in the presence of disorder
scattering. We show that size quantization patterns are only present when SU(2)
pseudospin symmetry is preserved. Symmetry breaking disorder renders transverse
quantization invisible, which may provide an explanation for the necessity of
suspending graphene nanoconstrictions to obtain size quantization signatures in
very recent experiments. Employing a quasi-classical Monte-Carlo simulation, we
are able to reproduce and explain key qualitative features of the full
quantum-mechanical calculations.Comment: 5 figure
Edge modes and non local conductance in graphene superlattices
We study the existence of edge modes in gapped Moir\'e superlattices in
graphene monolayer ribbons. We find that the superlattice bands acquire finite
Chern numbers, which lead to a Valley Hall Effect. The presence of dispersive
edge modes is confirmed by calculations of the band structure of realistic
nanoribbons using tight binding methods. These edge states are only weakly
sensitive to disorder, as short-range scattering processes lead to mean free
paths of the order of microns. The results explain the existence of edge
currents when the chemical potential lies within the bulk superlattice gap, and
offer an explanation for existing non-local resistivity measurements in
graphene ribbons on boron nitride
Conductance of graphene nanoribbon junctions and the tight binding model
Planar carbon-based electronic devices, including metal/semiconductor junctions, transistors and interconnects, can now be formed from patterned sheets of graphene. Most simulations of charge transport within graphene-based electronic devices assume an energy band structure based on a nearest-neighbour tight binding analysis. In this paper, the energy band structure and conductance of graphene nanoribbons and metal/semiconductor junctions are obtained using a third nearest-neighbour tight binding analysis in conjunction with an efficient nonequilibrium Green’s function formalism. We find significant differences in both the energy band structure and conductance obtained with the two approximations
Coherent transport through graphene nanoribbons in the presence of edge disorder
We simulate electron transport through graphene nanoribbons of experimentally
realizable size (length L up to 2 micrometer, width W approximately 40 nm) in
the presence of scattering at rough edges. Our numerical approach is based on a
modular recursive Green's function technique that features sub-linear scaling
with L of the computational effort. We identify the influence of the broken A-B
sublattice (or chiral) symmetry and of K-K' scattering by Fourier spectroscopy
of individual scattering states. For long ribbons we find Anderson-localized
scattering states with a well-defined exponential decay over 10 orders of
magnitude in amplitude.Comment: 8 pages, 6 Figure
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