397 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
Bipolar High Field Excitations in Co/Cu/Co Nanopillars
Current-induced magnetic excitations in Co/Cu/Co bilayer nanopillars
(50 nm in diameter) have been studied experimentally at low temperatures
for large applied fields perpendicular to the layers. At sufficiently high
current densities excitations, which lead to a decrease in differential
resistance, are observed for both current polarities. Such bipolar excitations
are not expected in a single domain model of spin-transfer. We propose that at
high current densities strong asymmetries in the longitudinal spin accumulation
cause spin-wave instabilities transverse to the current direction in bilayer
samples, similar to those we have reported for single magnetic layer junctions.Comment: 4 pages, 4 figures+ 2 additional jpg figures (Fig. 2d and Fig. 3)
high resolution figures and recent related articles are available at:
http://www.physics.nyu.edu/kentlab/news.htm
Energy Band Gap Engineering of Graphene Nanoribbons
We investigate electronic transport in lithographically patterned graphene
ribbon structures where the lateral confinement of charge carriers creates an
energy gap near the charge neutrality point. Individual graphene layers are
contacted with metal electrodes and patterned into ribbons of varying widths
and different crystallographic orientations. The temperature dependent
conductance measurements show larger energy gaps opening for narrower ribbons.
The sizes of these energy gaps are investigated by measuring the conductance in
the non-linear response regime at low temperatures. We find that the energy gap
scales inversely with the ribbon width, thus demonstrating the ability to
engineer the band gap of graphene nanostructures by lithographic processes.Comment: 7 pages including 4 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
Dependence of quantum-Hall conductance on the edge-state equilibration position in a bipolar graphene sheet
By using four-terminal configurations, we investigated the dependence of
longitudinal and diagonal resistances of a graphene p-n interface on the
quantum-Hall edge-state equilibration position. The resistance of a p-n device
in our four-terminal scheme is asymmetric with respect to the zero point where
the filling factor () of the entire graphene vanishes. This resistance
asymmetry is caused by the chiral-direction-dependent change of the
equilibration position and leads to a deeper insight into the equilibration
process of the quantum-Hall edge states in a bipolar graphene system.Comment: 5 pages, 4 figures, will be published in PR
Symmetry breaking and friction in few layer phosphorene
National Defense Science and Engineering Graduate Fellowshi
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