99 research outputs found
Enhanced Transmission Due to Disorder
The transmissivity of a one-dimensional random system that is periodic on
average is studied. It is shown that the transmission coefficient for
frequencies corresponding to a gap in the band structure of the average
periodic system increases with increasing disorder while the disorder is weak
enough. This property is shown to be universal, independent of the type of
fluctuations causing the randomness. In the case of strong disorder the
transmission coefficient for frequencies in allowed bands is found to be a non
monotonic function of the strength of the disorder. An explanation for the
latter behavior is provided.Comment: 9 pages, RevTeX 3.0, 4 Postscript figure
Random Surfaces that Suppress Single Scattering
We present a method for generating numerically a one-dimensional random
surface, defined by the equation x_3 = \zx, that suppresses single-scattering
processes in the scattering of light from it within a specified range of
scattering angles. Rigorous numerical calculations of the scattering of light
from surfaces generated by this approach show that the single-scattering
contribution to the mean scattered intensity is indeed suppressed within that
range of angles.Comment: 3 pagers (Latex), 3 figure
Soliton Propagation in Chains with Simple Nonlocal Defects
We study the propagation of solitons on complex chains built by inserting
finite graphs at two sites of an unbranched chain. We compare numerical
findings with the results of an analytical linear approximation scheme
describing the interaction of large-fast solitons with non-local topological
defects on a chain. We show that the transmission properties of the solitons
strongly depend on the structure of the inserted graph, giving a tool to
control the soliton propagation through the choice of pertinent graphs to be
attached to the chain.Comment: Published in the special issue of Physica D from a conference on
'Nonlinear Physics: Condensed Matter, Dynamical Systems and Biophysics' held
in honour of Serge Aubr
A new application of reduced Rayleigh equations to electromagnetic wave scattering by two-dimensional randomly rough surfaces
The small perturbations method has been extensively used for waves scattering
by rough surfaces. The standard method developped by Rice is difficult to apply
when we consider second and third order of scattered fields as a function of
the surface height. Calculations can be greatly simplified with the use of
reduced Rayleigh equations, because one of the unknown fields can be
eliminated. We derive a new set of four reduced equations for the scattering
amplitudes, which are applied to the cases of a rough conducting surface, and
to a slab where one of the boundary is a rough surface. As in the
one-dimensional case, numerical simulations show the appearance of enhanced
backscattering for these structures.Comment: RevTeX 4 style, 38 pages, 16 figures, added references and comments
on the satellites peak
Resonant tunneling of electromagnetic waves through polariton gaps
We consider resonant tunneling of electromagnetic waves through an optical
barrier formed by dielectric layers with the frequency dispersion of their
dielectric permiability. The frequency region between lower and upper polariton
branches in these materials presents a stop band for electromagnetic waves. We
show that resonance tunneling through this kind of barriers is qualitatevely
different from tunneling through other kind of optical barriers as well as from
quantum mechanic tunneling through a rectangular barrier. We find that the
width of the resonance maxima of the transmission coeffcient tends to zero as
frequency approach the lower boundary of the stop band in a very sharp
non-analytical way. Resonance transmission peaks give rise to new photonic
bands inside the stop band if one considers periodical array of the layers.Comment: 8 pages, 5 figure
Onset of Delocalization in Quasi-1D Waveguides with Correlated Surface Disorder
We present first analytical results on transport properties of many-mode
waveguides with rough surfaces having long-range correlations. We show that
propagation of waves through such waveguides reveals a quite unexpected
phenomena of a complete transparency for a subset of propagating modes. These
modes do not interact with each other and effectively can be described by the
theory of 1D transport with correlated disorder. We also found that with a
proper choice of model parameters one can arrange a perfect transparency of
waveguides inside a given window of energy of incoming waves. The results may
be important in view of experimental realizations of a selective transport in
application to both waveguides and electron/optic nanodevices.Comment: RevTex, 4 pages, no figures, few references are adde
Intensity Distribution of Modes in Surface Corrugated Waveguides
Exact calculations of transmission and reflection coefficients in surface
randomly corrugated optical waveguides are presented. As the length of the
corrugated part of the waveguide increases, there is a strong preference to
forward coupling through the lowest mode. An oscillating behavior of the
enhanced backscattering as a function of the wavelength is predicted. Although
the transport is strongly non isotropic, the analysis of the probability
distributions of the transmitted waves confirms in this configuration
distributions predicted by Random Matrix Theory for volume disorder
Long-range order and low-energy spectrum of diluted 2D quantum AF
The problem of diluted two-dimensional (2D) quantum antiferromagnet (AF) on a
square lattice is studied using spin-wave theory. The influence of impurities
on static and dynamic properties is investigated and a good agreement with
experiments and Monte Carlo (MC) data is found. The hydrodynamic description of
spin-waves breaks down at characteristic wavelengths
\Lambda\agt\exp(\frac{const}{x}), being an impurity concentration, while
the order parameter is free from anomalies. We argue that this dichotomy
originates from strong scattering of the low-energy excitations in 2D.Comment: PRL Award received, 4 pages, 3 figure
Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders
In this Letter, we present a theoretical analysis of the acoustic
transmission through two-dimensional arrays of straight rigid cylinders placed
parallelly in the air. Both periodic and completely random arrangements of the
cylinders are considered. The results for the sound attenuation through the
periodic arrays are shown to be in a remarkable agreement with the reported
experimental data. As the arrangement of the cylinders is randomized, the
transmission is significantly reduced for a wider range of frequencies. For the
periodic arrays, the acoustic band structures are computed by the plane-wave
expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure
Mobility Edge in Aperiodic Kronig-Penney Potentials with Correlated Disorder: Perturbative Approach
It is shown that a non-periodic Kronig-Penney model exhibits mobility edges
if the positions of the scatterers are correlated at long distances. An
analytical expression for the energy-dependent localization length is derived
for weak disorder in terms of the real-space correlators defining the
structural disorder in these systems. We also present an algorithm to construct
a non-periodic but correlated sequence exhibiting desired mobility edges. This
result could be used to construct window filters in electronic, acoustic, or
photonic non-periodic structures.Comment: RevTex, 4 pages including 2 Postscript figure
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