143 research outputs found
Electron Clusters in Inert Gases
The paper addresses counterintuitive behavior of electrons injected into
dense cryogenic media with negative scattering length . Instead of
expected polaronic effect (formation of density enhancement clusters) which
should substantially reduce the electron mobility, an opposite picture is
observed: with increasing (the trend taking place for inert gases with
the growth of atomic number) and the medium density, the electrons remain
practically free. An explanation of this behaviour is provided based on
consistent accounting for the non-linearity of electron interaction with the
gaseous medium in the gas atom number density
Novel Edge Excitations of Two-dimensional Electron Liquid in a Magnetic Field
We investigate the low-energy spectrum of excitations of a compressible
electron liquid in a strong magnetic field. These excitations are localized at
the periphery of the system. The analysis of a realistic model of a smooth edge
yields new branches of acoustic excitation spectrum in addition to the well
known edge magnetoplasmon mode. The velocities are found and the observability
conditions are established for the new modes.Comment: 9 pages + 2 figures by request preprint TPI-MINN-93/59-
Magnetoplasmon excitations in arrays of circular and noncircular quantum dots
We have investigated the magnetoplasmon excitations in arrays of circular and
noncircular quantum dots within the Thomas-Fermi-Dirac-von Weizs\"acker
approximation. Deviations from the ideal collective excitations of isolated
parabolically confined electrons arise from local perturbations of the
confining potential as well as interdot Coulomb interactions. The latter are
unimportant unless the interdot separations are of the order of the size of the
dots. Local perturbations such as radial anharmonicity and noncircular symmetry
lead to clear signatures of the violation of the generalized Kohn theorem. In
particular, the reduction of the local symmetry from SO(2) to results in
a resonant coupling of different modes and an observable anticrossing behaviour
in the power absorption spectrum. Our results are in good agreement with recent
far-infrared (FIR) transmission experiments.Comment: 25 pages, 6 figures, typeset in RevTe
Quantum Cryptography Based on the Time--Energy Uncertainty Relation
A new cryptosystem based on the fundamental time--energy uncertainty relation
is proposed. Such a cryptosystem can be implemented with both correlated photon
pairs and single photon states.Comment: 5 pages, LaTex, no figure
Relativistic Restrictions on the Distinguishability of Orthogonal Quantum States
We analyze the restrictions on the distinguishability of quantum states
imposed by special relativity. An explicit expression relating the error
probability for distinguishing between two orthogonal single-photon states with
the time elapsed from the start of the measurement procedure until the
measurement result is obtained by the observer.Comment: 9 pages, 1 figure (misprints in formulas corrected
Маркетинг навколишнього середовища
The photophysical properties of silicon semiconductor nanocrystals (SiNCs) are extremely sensitive to the presence of surface chemical defects, many of which are easily produced by oxidation under ambient conditions. The diversity of chemical structures of such defects and the lack of tools capable of probing individual defects continue to impede understanding of the roles of these defects in SiNC photophysics. We use scanning tunneling spectroscopy to study the impact of surface defects on the electronic structures of hydrogen-passivated SiNCs supported on the Au(111) surface. Spatial maps of the local electronic density of states (LDOS) produced by our measurements allowed us to identify locally enhanced defect-induced states as well as quantum-confined states delocalized throughout the SiNC volume. We use theoretical calculations to show that the LDOS spectra associated with the observed defects are attributable to Si-O-Si bridged oxygen or Si-OH surface defects
Transport properties of copper phthalocyanine based organic electronic devices
Ambipolar charge carrier transport in Copper phthalocyanine (CuPc) is studied
experimentally in field-effect transistors and metal-insulator-semiconductor
diodes at various temperatures. The electronic structure and the transport
properties of CuPc attached to leads are calculated using density functional
theory and scattering theory at the non-equilibrium Green's function level. We
discuss, in particular, the electronic structure of CuPc molecules attached to
gold chains in different geometries to mimic the different experimental setups.
The combined experimental and theoretical analysis explains the dependence of
the mobilityand the transmission coefficient on the charge carrier type
(electrons or holes) and on the contact geometry. We demonstrate the
correspondence between our experimental results on thick films and our
theoretical studies of single molecule contacts. Preliminary results for
fluorinated CuPc are discussed.Comment: 18 pages, 16 figures; to be published in Eur. Phys. J. Special Topic
Gravitational Waves from Gravitational Collapse
Gravitational wave emission from the gravitational collapse of massive stars
has been studied for more than three decades. Current state of the art
numerical investigations of collapse include those that use progenitors with
realistic angular momentum profiles, properly treat microphysics issues,
account for general relativity, and examine non--axisymmetric effects in three
dimensions. Such simulations predict that gravitational waves from various
phenomena associated with gravitational collapse could be detectable with
advanced ground--based and future space--based interferometric observatories.Comment: 68 pages including 13 figures; revised version accepted for
publication in Living Reviews in Relativity (http://www.livingreviews.org
Gravitational Wave Astronomy: in Anticipation of First Sources to be Detected
The first generation of long-baseline laser interferometric detectors of
gravitational waves will start collecting data in 2001-2003. We carefully
analyse their planned performance and compare it with the expected strengths of
astrophysical sources. The scientific importance of the anticipated discovery
of various gravitatinal wave signals and the reliability of theoretical
predictions are taken into account in our analysis. We try to be conservative
both in evaluating the theoretical uncertainties about a source and the
prospects of its detection. After having considered many possible sources, we
place our emphasis on (1) inspiraling binaries consisting of stellar mass black
holes and (2) relic gravitational waves. We draw the conclusion that
inspiraling binary black holes are likely to be detected first by the initial
ground-based interferometers. We estimate that the initial interferometers will
see 2-3 events per year from black hole binaries with component masses
10-15M_\odot, with a signal-to-noise ratio of around 2-3, in each of a network
of detectors consisting of GEO, VIRGO and the two LIGOs. It appears that other
possible sources, including coalescing neutron stars, are unlikely to be
detected by the initial instruments. We also argue that relic gravitational
waves may be discovered by the space-based interferometers in the frequency
interval 2x10^{-3}-10^{-2} Hz, at the signal-to-noise ratio level around 3.Comment: latex, 100 pages, including 20 postscript figures. Small typos
corrected, references adde
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