1,476 research outputs found
An Evaluation of the Optical Maser Photon Rate Gyroscope
Mathematical development of resonant frequencies of electromagnetic cavity - Evaluation of optical maser photon rate gyroscop
Adiabatic orientation of rotating dipole molecules in an external field
The induced polarization of a beam of polar clusters or molecules passing
through an electric or magnetic field region differs from the textbook
Langevin-Debye susceptibility. This distinction, which is important for the
interpretation of deflection and focusing experiments, arises because instead
of acquiring thermal equilibrium in the field region, the beam ensemble
typically enters the field adiabatically, i.e., with a previously fixed
distribution of rotational states. We discuss the orientation of rigid
symmetric-top systems with a body-fixed electric or magnetic dipole moment. The
analytical expression for their "adiabatic-entry" orientation is elucidated and
compared with exact numerical results for a range of parameters. The
differences between the polarization of thermodynamic and "adiabatic-entry"
ensembles, of prolate and oblate tops, and of symmetric-top and linear rotators
are illustrated and identified.Comment: 18 pages, 4 figure
Non-invasive nanoscale potentiometry and ballistic transport in epigraphene nanoribbons
The recent observation of non-classical electron transport regimes in
two-dimensional materials has called for new high-resolution non-invasive
techniques to locally probe electronic properties. We introduce a novel hybrid
scanning probe technique to map the local resistance and electrochemical
potential with nm- and V resolution, and we apply it to study epigraphene
nanoribbons grown on the sidewalls of SiC substrate steps. Remarkably, the
potential drop is non uniform along the ribbons, and m-long segments show
no potential variation with distance. The potential maps are in excellent
agreement with measurements of the local resistance. This reveals ballistic
transport in ambient condition, compatible with micrometer-long
room-temperature electronic mean free paths
Multiple plasmon resonances in naturally-occurring multiwall nanotubes: infrared spectra of chrysotile asbestos
Chrysotile asbestos is formed by densely packed bundles of multiwall hollow
nanotubes. Each wall in the nanotubes is a cylindrically wrapped layer of . We show by experiment and theory that the infrared spectrum
of chrysotile presents multiple plasmon resonances in the Si-O stretching
bands. These collective charge excitations are universal features of the
nanotubes that are obtained by cylindrically wrapping an anisotropic material.
The multiple plasmons can be observed if the width of the resonances is
sufficiently small as in chrysotile.Comment: 4 pages, 5 figures. Revtex4 compuscript. Misprint in Eq.(6) correcte
Multiparticle Clusters and Intermittent Fluctuations
An approach for understanding the behavior of multiplicity distributions in
restricted phase-space intervals derived on the basis of global observables is
proposed. We obtain a unifying connection between local multiparticle clusters
and the scale-invariant power-law behavior of normalized factorial moments. The
model can be used to describe multiparticle processes in terms of a
decomposition of the observed intermittent signal into contributions from
clusters with varying number of particles.Comment: 13 pages, LaTeX, 3 figures, epsfig.sty, cite.sty, Presented at 5th
Ann. Int. Seminar ``Non-Linear Phenomena in Complex Systems'' Minsk, Belarus,
February 199
Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene
We report results from two-dimensional Raman spectroscopy studies of
large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large
variation in Raman peak position across the sample resulting from inhomogeneity
in the strain of the graphene film, which we show to be correlated with
physical topography by coupling Raman spectroscopy with atomic force
microscopy. We report that essentially strain free graphene is possible even
for epitaxial graphene.Comment: 10 pages, 3 figure
Semiclassical theory for spatial density oscillations in fermionic systems
We investigate the particle and kinetic-energy densities for a system of
fermions bound in a local (mean-field) potential V(\bfr). We generalize a
recently developed semiclassical theory [J. Roccia and M. Brack, Phys. Rev.\
Lett. {\bf 100}, 200408 (2008)], in which the densities are calculated in terms
of the closed orbits of the corresponding classical system, to
dimensions. We regularize the semiclassical results for the U(1) symmetry
breaking occurring for spherical systems at and near the classical
turning points where the Friedel oscillations are predominant and well
reproduced by the shortest orbit going from to the closest turning point
and back. For systems with spherical symmetry, we show that there exist two
types of oscillations which can be attributed to radial and non-radial orbits,
respectively. The semiclassical theory is tested against exact
quantum-mechanical calculations for a variety of model potentials. We find a
very good overall numerical agreement between semiclassical and exact numerical
densities even for moderate particle numbers . Using a "local virial
theorem", shown to be valid (except for a small region around the classical
turning points) for arbitrary local potentials, we can prove that the
Thomas-Fermi functional reproduces the oscillations in
the quantum-mechanical densities to first order in the oscillating parts.Comment: LaTeX, 22pp, 15 figs, 1 table, to be published in Phys. Rev.
Directed self-organization of graphene nanoribbons on SiC
Realization of post-CMOS graphene electronics requires production of
semiconducting graphene, which has been a labor-intensive process. We present
tailoring of silicon carbide crystals via conventional photolithography and
microelectronics processing to enable templated graphene growth on
4H-SiC{1-10n} (n = 8) crystal facets rather than the customary {0001} planes.
This allows self-organized growth of graphene nanoribbons with dimensions
defined by those of the facet. Preferential growth is confirmed by Raman
spectroscopy and high-resolution transmission electron microscopy (HRTEM)
measurements, and electrical characterization of prototypic graphene devices is
presented. Fabrication of > 10,000 top-gated graphene transistors on a 0.24 cm2
SiC chip demonstrates scalability of this process and represents the highest
density of graphene devices reported to date.Comment: 13 pages, 5 figure
Formalism for Multiphoton Plasmon Excitation in Jellium Clusters
We present a new formalism for the description of multiphoton plasmon
excitation processes in jellium clusters. By using our method, we demonstrate
that, in addition to dipole plasmon excitations, the multipole plasmons
(quadrupole, octupole, etc) can be excited in a cluster by multiphoton
absorption processes, which results in a significant difference between plasmon
resonance profiles in the cross sections for multiphoton as compared to
single-photon absorption. We calculate the cross sections for multiphoton
absorption and analyse the balance between the surface and volume plasmon
contributions to multipole plasmons.Comment: 29 pages, 1 figur
Electronic entropy, shell structure, and size-evolutionary patterns of metal clusters
We show that electronic-entropy effects in the size-evolutionary patterns of
relatively small (as small as 20 atoms), simple-metal clusters become prominent
already at moderate temperatures. Detailed agreement between our
finite-temperature-shell-correction-method calculations and experimental
results is obtained for certain temperatures. This agreement includes a
size-dependent smearing out of fine-structure features, accompanied by a
measurable reduction of the heights of the steps marking major-shell and
subshell closings, thus allowing for a quantitative analysis of cluster
temperatures.Comment: Latex/Revtex, 4 pages with 3 Postscript figure
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