385 research outputs found
Electronic transport in locally gated graphene nanoconstrictions
We have developed the combination of an etching and deposition technique that
enables the fabrication of locally gated graphene nanostructures of arbitrary
design. Employing this method, we have fabricated graphene nanoconstrictions
with local tunable transmission and characterized their electronic properties.
An order of magnitude enhanced gate efficiency is achieved adopting the local
gate geometry with thin dielectric gate oxide. A complete turn off of the
device is demonstrated as a function of the local gate voltage. Such strong
suppression of device conductance was found to be due to both quantum
confinement and Coulomb blockade effects in the constricted graphene
nanostructures.Comment: 3 pages 3 figures; separated and expanded from arXiv:0705.3044v
Electronic Transport in Dual-gated Bilayer Graphene at Large Displacement Fields
We study the electronic transport properties of dual-gated bilayer graphene
devices. We focus on the regime of low temperatures and high electric
displacement fields, where we observe a clear exponential dependence of the
resistance as a function of displacement field and density, accompanied by a
strong non-linear behavior in the transport characteristics. The effective
transport gap is typically two orders of magnitude smaller than the optical
band gaps reported by infrared spectroscopy studies. Detailed temperature
dependence measurements shed light on the different transport mechanisms in
different temperature regimes.Comment: 4 pages, 3 figure
Single electron tunneling through high-Q single-wall carbon nanotube NEMS resonators
By first lithographically fabricating contact electrodes and then as last
step growing carbon nanotubes with chemical vapour deposition across the
ready-made chip, many potential contamination mechanisms for nanotube devices
can be avoided. Combining this with pre-defined trenches on the chip, such that
the nanotubes are freely suspended above the substrate, enables the formation
of highly regular electronic systems. We show that, in addition, such suspended
ultra-clean nanotubes provide excellent high-frequency and low-dissipation
mechanical resonators. The motion detection mechanism of our experiment is
discussed, and we measure the effect of Coulomb blockade and the back-action of
single electron tunneling on the mechanical motion. In addition data on the
mechanical higher modes is presented.Comment: 7 pages, 6 figure
Excited state spectroscopy in carbon nanotube double quantum dots
We report on low temperature measurements in a fully tunable carbon nanotube
double quantum dot. A new fabrication technique has been used for the top-gates
in order to avoid covering the whole nanotube with an oxide layer as in
previous experiments. The top-gates allow us to form single dots, control the
coupling between them and we observe four-fold shell filling. We perform
inelastic transport spectroscopy via the excited states in the double quantum
dot, a necessary step towards the implementation of new microwave-based
experiments.Comment: 16 pages, 6 figures, submitted to nanoletter
Long wavelength local density of states oscillations near graphene step edges
Using scanning tunneling microscopy and spectroscopy, we have studied the
local density of states (LDOS) of graphene over step edges in boron nitride.
Long wavelength oscillations in the LDOS are observed with maxima parallel to
the step edge. Their wavelength and amplitude are controlled by the energy of
the quasiparticles allowing a direct probe of the graphene dispersion relation.
We also observe a faster decay of the LDOS oscillations away from the step edge
than in conventional metals. This is due to the chiral nature of the Dirac
fermions in graphene.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
Quantum Hall Effect, Screening and Layer-Polarized Insulating States in Twisted Bilayer Graphene
We investigate electronic transport in dual-gated twisted bilayer graphene.
Despite the sub-nanometer proximity between the layers, we identify independent
contributions to the magnetoresistance from the graphene Landau level spectrum
of each layer. We demonstrate that the filling factor of each layer can be
independently controlled via the dual gates, which we use to induce Landau
level crossings between the layers. By analyzing the gate dependence of the
Landau level crossings, we characterize the finite inter-layer screening and
extract the capacitance between the atomically-spaced layers. At zero filling
factor, we observe magnetic and displacement field dependent insulating states,
which indicate the presence of counter-propagating edge states with inter-layer
coupling.Comment: 4 pages, 3 figure
Electronic transport and quantum Hall effect in bipolar graphene p-n-p junction
We have developed a device fabrication process to pattern graphene into
nanostructures of arbitrary shape and control their electronic properties using
local electrostatic gates. Electronic transport measurements have been used to
characterize locally gated bipolar graphene -- junctions. We observe a
series of fractional quantum Hall conductance plateaus at high magnetic fields
as the local charge density is varied in the and regions. These
fractional plateaus, originating from chiral edge states equilibration at the
- interfaces, exhibit sensitivity to inter-edge backscattering which is
found to be strong for some of the plateuas and much weaker for other plateaus.
We use this effect to explore the role of backscattering and estimate disorder
strength in our graphene devices.Comment: 4 pages 4 figures, to appear in Phys. Rev. Lett. Original version
arXiv:0705.3044v1 was separated and expanded to this current version and
arXiv:0709.173
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