617 research outputs found
Graphene as an electronic membrane
Experiments are finally revealing intricate facts about graphene which go
beyond the ideal picture of relativistic Dirac fermions in pristine two
dimensional (2D) space, two years after its first isolation. While observations
of rippling added another dimension to the richness of the physics of graphene,
scanning single electron transistor images displayed prevalent charge
inhomogeneity. The importance of understanding these non-ideal aspects cannot
be overstated both from the fundamental research interest since graphene is a
unique arena for their interplay, and from the device applications interest
since the quality control is a key to applications. We investigate the membrane
aspect of graphene and its impact on the electronic properties. We show that
curvature generates spatially varying electrochemical potential. Further we
show that the charge inhomogeneity in turn stabilizes ripple formation.Comment: 6 pages, 11 figures. Updated version with new results about the
re-hybridization of the electronic orbitals due to rippling of the graphene
sheet. The re-hybridization adds the next-to-nearest neighbor hopping effect
discussed in the previous version. New reference to recent STM experiments
that give support to our theor
Wavenumber Spectrum in the Gulf Stream from Shipboard ADCP Observations and Comparison with Altimetry Measurements
The wavenumber spectra for velocity and temperature in the Gulf Stream region are calculated from a decade (1994–2004) of shipboard acoustic Doppler current profiler (ADCP) measurements taken as part of the Oleander Project. The velocity and temperature spectra have comparable magnitude, in terms of the kinetic and potential energy, and both indicate a k−3 slope in the mesoscales. In contrast, the corresponding velocity spectrum determined from satellite altimetry sea surface heights yields a significantly higher energy level and a k−2 slope. The discrepancy between altimeter-derived and directly measured velocity spectra suggests that altimetric velocity probably is contaminated by noise in sea surface height measurement. Also, the k−3 slope, which appears to be in agreement with two-dimensional quasigeostrophic turbulence theory, does not support the contemporary surface quasigeostrophic theory. These results highlight large gaps in the current understanding of the nature of surface geostrophic turbulence
Low Energy Electron Point Projection Microscopy of Suspended Graphene, the Ultimate "Microscope Slide"
Point Projection Microscopy (PPM) is used to image suspended graphene using
low-energy electrons (100-200eV). Because of the low energies used, the
graphene is neither damaged or contaminated by the electron beam. The
transparency of graphene is measured to be 74%, equivalent to electron
transmission through a sheet as thick as twice the covalent radius of
sp^2-bonded carbon. Also observed is rippling in the structure of the suspended
graphene, with a wavelength of approximately 26 nm. The interference of the
electron beam due to the diffraction off the edge of a graphene knife edge is
observed and used to calculate a virtual source size of 4.7 +/- 0.6 Angstroms
for the electron emitter. It is demonstrated that graphene can be used as both
anode and substrate in PPM in order to avoid distortions due to strong field
gradients around nano-scale objects. Graphene can be used to image objects
suspended on the sheet using PPM, and in the future, electron holography
The inverse nullity pair problem and the strong nullity interlacing property
The inverse eigenvalue problem studies the possible spectra among matrices
whose off-diagonal entries have their zero-nonzero patterns described by the
adjacency of a graph . In this paper, we refer to the -nullity pair of a
matrix as , where
is the matrix obtained from by removing the -th row and column.
The inverse -nullity pair problem is considered for complete graphs, cycles,
and trees. The strong nullity interlacing property is introduced, and the
corresponding supergraph lemma and decontraction lemma are developed as new
tools for constructing matrices with a given nullity pair
Manipulation of graphene's dynamic ripples by local harmonic out-of-plane excitation
With use of carefully designed molecular dynamics simulations, we demonstrate
tuning of dynamic ripples in free-standing graphene by applying a local
out-of-plane sinusoidal excitation. Depending on the boundary conditions and
external modulation, we show control of the local dynamic morphology, including
flattening and stable rippling patterns. In addition to studying the dynamic
response of atomically thin layers to external time-varying excitation, our
results open intriguing possibilities for modulating their properties via local
dynamic morphology control
Non-resonant dot-cavity coupling and its applications in resonant quantum dot spectroscopy
We present experimental investigations on the non-resonant dot-cavity
coupling of a single quantum dot inside a micro-pillar where the dot has been
resonantly excited in the s-shell, thereby avoiding the generation of
additional charges in the QD and its surrounding. As a direct proof of the pure
single dot-cavity system, strong photon anti-bunching is consistently observed
in the autocorrelation functions of the QD and the mode emission, as well as in
the cross-correlation function between the dot and mode signals. Strong Stokes
and anti-Stokes-like emission is observed for energetic QD-mode detunings of up
to ~100 times the QD linewidth. Furthermore, we demonstrate that non-resonant
dot-cavity coupling can be utilized to directly monitor and study relevant QD
s-shell properties like fine-structure splittings, emission saturation and
power broadening, as well as photon statistics with negligible background
contributions. Our results open a new perspective on the understanding and
implementation of dot-cavity systems for single-photon sources, single and
multiple quantum dot lasers, semiconductor cavity quantum electrodynamics, and
their implementation, e.g. in quantum information technology.Comment: 17 pages, 4 figure
UNOLS Establishes SCOAR to Promote Research Aircraft Facilities for U.S. Ocean Sciences
Oceanography, Vol. 17, No. 4, pp. 176-185, December 2004
On-demand semiconductor single-photon source with near-unity indistinguishability
Single photon sources based on semiconductor quantum dots offer distinct
advantages for quantum information, including a scalable solid-state platform,
ultrabrightness, and interconnectivity with matter qubits. A key prerequisite
for their use in optical quantum computing and solid-state networks is a high
level of efficiency and indistinguishability. Pulsed resonance fluorescence
(RF) has been anticipated as the optimum condition for the deterministic
generation of high-quality photons with vanishing effects of dephasing. Here,
we generate pulsed RF single photons on demand from a single,
microcavity-embedded quantum dot under s-shell excitation with 3-ps laser
pulses. The pi-pulse excited RF photons have less than 0.3% background
contributions and a vanishing two-photon emission probability.
Non-postselective Hong-Ou-Mandel interference between two successively emitted
photons is observed with a visibility of 0.97(2), comparable to trapped atoms
and ions. Two single photons are further used to implement a high-fidelity
quantum controlled-NOT gate.Comment: 11 pages, 11 figure
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