440 research outputs found
Resonance effects due to the excitation of surface Josephson plasma waves in layered superconductors
We analytically examine the excitation of surface Josephson plasma waves
(SJPWs) in periodically-modulated layered superconductors. We show that the
absorption of the incident electromagnetic wave can be substantially increased,
for certain incident angles, due to the resonance excitation of SJPWs. The
absorption increase is accompanied by the decrease of the specular reflection.
Moreover, we find the physical conditions guaranteeing the total absorption
(and total suppression of the specular reflection). These conditions can be
realized for Bi2212 superconductor films.Comment: 17 pages, 3 figure
Optical Study of GaAs quantum dots embedded into AlGaAs nanowires
We report on the photoluminescence characterization of GaAs quantum dots
embedded into AlGaAs nano-wires. Time integrated and time resolved
photoluminescence measurements from both an array and a single quantum
dot/nano-wire are reported. The influence of the diameter sizes distribution is
evidenced in the optical spectroscopy data together with the presence of
various crystalline phases in the AlGaAs nanowires.Comment: 5 page, 5 figure
Excitation of surface plasmon-polaritons in metal films with double periodic modulation: anomalous optical effects
We perform a thorough theoretical analysis of resonance effects when an
arbitrarily polarized plane monochromatic wave is incident onto a double
periodically modulated metal film sandwiched by two different transparent
media. The proposed theory offers a generalization of the theory that had been
build in our recent papers for the simplest case of one-dimensional structures
to two-dimensional ones. A special emphasis is placed on the films with the
modulation caused by cylindrical inclusions, hence, the results obtained are
applicable to the films used in the experiments. We discuss a spectral
composition of modulated films and highlight the principal role of
``resonance'' and ``coupling'' modulation harmonics. All the originating
multiple resonances are examined in detail. The transformation coefficients
corresponding to different diffraction orders are investigated in the vicinity
of each resonance. We make a comparison between our theory and recent
experiments concerning enhanced light transmittance and show the ways of
increasing the efficiency of these phenomena. In the appendix we demonstrate a
close analogy between ELT effect and peculiarities of a forced motion of two
coupled classical oscillators.Comment: 24 pages, 17 figure
Dynamic Fluctuation Phenomena in Double Membrane Films
Dynamics of double membrane films is investigated in the long-wavelength
limit including the overdamped squeezing mode. We demonstrate that thermal
fluctuations essentially modify the character of the mode due to its nonlinear
coupling to the transversal shear hydrodynamic mode. The corresponding Green
function acquires as a function of the frequency a cut along the imaginary
semi-axis. Fluctuations lead to increasing the attenuation of the squeezing
mode it becomes larger than the `bare' value.Comment: 7 pages, Revte
Finite temperature Casimir effect for graphene
We adopt the Dirac model for quasiparticles in graphene and calculate the
finite temperature Casimir interaction between a suspended graphene layer and a
parallel conducting surface. We find that at high temperature the Casimir
interaction in such system is just one half of that for two ideal conductors
separated by the same distance. In this limit single graphene layer behaves
exactly as a Drude metal. In particular, the contribution of the TE mode is
suppressed, while one of the TM mode saturates the ideal metal value. Behaviour
of the Casimir interaction for intermediate temperatures and separations
accessible for an experiment is studied in some detail. We also find an
interesting interplay between two fundamental constants of graphene physics:
the fine structure constant and the Fermi velocity.Comment: 13 pages, 2 figures, to appear in Physical Review
Large Charge Four-Dimensional Extremal N=2 Black Holes with R^2-Terms
We consider N=2 supergravity in four dimensions with small R^2 curvature
corrections. We construct large charge extremal supersymmetric and
non-supersymmetric black hole solutions in all space, and analyze their
thermodynamic properties.Comment: 18 pages. v2,3: minor fixe
Exact Resummations in the Theory of Hydrodynamic Turbulence: I The Ball of Locality and Normal Scaling
This paper is the first in a series of three papers that aim at understanding
the scaling behaviour of hydrodynamic turbulence. We present in this paper a
perturbative theory for the structure functions and the response functions of
the hydrodynamic velocity field in real space and time. Starting from the
Navier-Stokes equations (at high Reynolds number Re) we show that the standard
perturbative expansions that suffer from infra-red divergences can be exactly
resummed using the Belinicher-L'vov transformation. After this exact (partial)
resummation it is proven that the resulting perturbation theory is free of
divergences, both in large and in small spatial separations. The hydrodynamic
response and the correlations have contributions that arise from mediated
interactions which take place at some space- time coordinates. It is shown that
the main contribution arises when these coordinates lie within a shell of a
"ball of locality" that is defined and discussed. We argue that the real
space-time formalism developed here offers a clear and intuitive understanding
of every diagram in the theory, and of every element in the diagrams. One major
consequence of this theory is that none of the familiar perturbative mechanisms
may ruin the classical Kolmogorov (K41) scaling solution for the structure
functions. Accordingly, corrections to the K41 solutions should be sought in
nonperturbative effects. These effects are the subjects of papers II and III in
this series, that will propose a mechanism for anomalous scaling in turbulence,
which in particular allows multiscaling of the structure functions.Comment: PRE in press, 18 pages + 6 figures, REVTeX. The Eps files of figures
will be FTPed by request to [email protected]
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