110 research outputs found
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
Diffractive wave guiding of hot electrons by the Au (111) herringbone reconstruction
The surface potential of the herringbone reconstruction on Au(111) is known
to guide surface-state electrons along the potential channels. Surprisingly, we
find by scanning tunneling spectroscopy that hot electrons with kinetic
energies twenty times larger than the potential amplitude (38 meV) are still
guided. The efficiency even increases with kinetic energy, which is reproduced
by a tight binding calculation taking the known reconstruction potential and
strain into account. The guiding is explained by diffraction at the
inhomogeneous electrostatic potential and strain distribution provided by the
reconstruction.Comment: 10 pages, 9 figure
Electron-Hole Crossover in Graphene Quantum Dots
We investigate the addition spectrum of a graphene quantum dot in the
vicinity of the electron-hole crossover as a function of perpendicular magnetic
field. Coulomb blockade resonances of the 50 nm wide dot are visible at all
gate voltages across the transport gap ranging from hole to electron transport.
The magnetic field dependence of more than 50 states displays the unique
complex evolution of the diamagnetic spectrum of a graphene dot from the
low-field regime to the Landau regime with the n=0 Landau level situated in the
center of the transport gap marking the electron-hole crossover. The average
peak spacing in the energy region around the crossover decreases with
increasing magnetic field. In the vicinity of the charge neutrality point we
observe a well resolved and rich excited state spectrum.Comment: 4 pages, 3 figure
Negative quantum capacitance in graphene nanoribbons with lateral gates
We present numerical simulations of the capacitive coupling between graphene
nanoribbons of various widths and gate electrodes in different configurations.
We compare the influence of lateral metallic or graphene side gate structures
on the overall back gate capacitive coupling. Most interestingly, we find a
complex interplay between quantum capacitance effects in the graphene
nanoribbon and the lateral graphene side gates, giving rise to an
unconventional negative quantum capacitance. The emerging non-linear capacitive
couplings are investigated in detail. The experimentally relevant relative
lever arm, the ratio between the coupling of the different gate structures, is
discussed.Comment: 8 pages, 6 figure
- …