20 research outputs found
Tunable local polariton modes in semiconductors
We study the local states within the polariton bandgap that arise due to deep
defect centers with strong electron-phonon coupling. Electron transitions
involving deep levels may result in alteration of local elastic constants. In
this case, substantial reversible transformations of the impurity polariton
density of states occur, which include the appearance/disappearance of the
polariton impurity band, its shift and/or the modification of its shape. These
changes can be induced by thermo- and photo-excitation of the localized
electron states or by trapping of injected charge carriers. We develop a simple
model, which is applied to the center in . Further possible
experimental realizations of the effect are discussed.Comment: 7 pages, 3 figure
Scaling Properties of 1D Anderson Model with Correlated Diagonal Disorder
Statistical and scaling properties of the Lyapunov exponent for a
tight-binding model with the diagonal disorder described by a dichotomic
process are considered near the band edge. The effect of correlations on
scaling properties is discussed. It is shown that correlations lead to an
additional parameter governing the validity of single parameter scaling.Comment: 5 pages, 3 figures, RevTe
Effects of inhomogeneous broadening on reflection spectra of Bragg multiple quantum well structures with a defect
The reflection spectrum of a multiple quantum well structure with an inserted
defect well is considered. The defect is characterized by the exciton frequency
different from that of the host's wells. It is shown that for relatively short
structures, the defect produces significant modifications of the reflection
spectrum, which can be useful for optoelectronic applications. Inhomogeneous
broadening is shown to affect the spectrum in a non-trivial way, which cannot
be described by the standard linear dispersion theory. A method of measuring
parameters of both homogeneous and inhomogeneous broadenings of the defect well
from a single CW reflection spectrum is suggested.Comment: 27 pages, 6 eps figures; RevTe
Single parameter scaling in 1-D localized absorbing systems
Numerical study of the scaling of transmission fluctuations in the 1-D
localization problem in the presence of absorption is carried out. Violations
of single parameter scaling for lossy systems are found and explained on the
basis of a new criterion for different types of scaling behavior derived by
Deych et al [Phys. Rev. Lett., {\bf 84}, 2678 (2000)].Comment: 7 pages, 6 figures, RevTex, submitted to Phys. Rev.
Statistics of Lyapunov exponent in one-dimensional layered systems
Localization of acoustic waves in a one dimensional water duct containing
many randomly distributed air filled blocks is studied. Both the Lyapunov
exponent and its variance are computed. Their statistical properties are also
explored extensively. The results reveal that in this system the single
parameter scaling is generally inadequate no matter whether the frequency we
consider is located in a pass band or in a band gap. This contradicts the
earlier observations in an optical case. We compare the results with two
optical cases and give a possible explanation of the origin of the different
behaviors.Comment: 6 pages revtex file, 6 eps figure
Sublocalization, superlocalization, and violation of standard single parameter scaling in the Anderson model
We discuss the localization behavior of localized electronic wave functions
in the one- and two-dimensional tight-binding Anderson model with diagonal
disorder. We find that the distributions of the local wave function amplitudes
at fixed distances from the localization center are well approximated by
log-normal fits which become exact at large distances. These fits are
consistent with the standard single parameter scaling theory for the Anderson
model in 1d, but they suggest that a second parameter is required to describe
the scaling behavior of the amplitude fluctuations in 2d. From the log-normal
distributions we calculate analytically the decay of the mean wave functions.
For short distances from the localization center we find stretched exponential
localization ("sublocalization") in both, 1d and 2d. In 1d, for large
distances, the mean wave functions depend on the number of configurations N
used in the averaging procedure and decay faster that exponentially
("superlocalization") converging to simple exponential behavior only in the
asymptotic limit. In 2d, in contrast, the localization length increases
logarithmically with the distance from the localization center and
sublocalization occurs also in the second regime. The N-dependence of the mean
wave functions is weak. The analytical result agrees remarkably well with the
numerical calculations.Comment: 12 pages with 9 figures and 1 tabl
Numerical verification of universality for the Anderson transition
We analyze the scaling behavior of the higher Lyapunov exponents at the
Anderson transition. We estimate the critical exponent and verify its
universality and that of the critical conductance distribution for box,
Gaussian and Lorentzian distributions of the random potential
Conductance of tubular nanowires with disorder
We calculate the conductance of tubular-shaped nanowires having many
potential scatterers at random positions. Our approach is based on the
scattering matrix formalism and our results analyzed within the scaling theory
of disordered conductors. When increasing the energy the conductance for a big
enough number of impurities in the tube manifests a systematic evolution from
the localized to the metallic regimes. Nevertheless, a conspicuous drop in
conductance is predicted whenever a new transverse channel is open. Comparison
with the semiclassical calculation leading to purely ohmic behavior is made.Comment: 8 pages, 5 figure
Self-consistent approach for excitons in quantum wells
We introduce a computationally efficient approach to calculating the
characteristics of excitons in quantum wells. In this approach we derive a
system of self-consistent equations describing the motion of an electron-hole
pair. The motion in the growth direction of the quantum well in this approach
is separated from the in-plane motion, but each of them occurs in modified
potentials found self-consistently. The approach is applied to shallow quantum
wells, for which we obtained an analytical expression for the exciton binding
energy and the ground state eigenfunction. Our results are in excellent
agreement with standard variational calculations, but require greatly reduced
computational effort.Comment: RevTeX4, 13 pages, 4 figures, submitted to Phys. Rev B Changed
content, added references, correct typo
Statistical properties of phases and delay times of the one-dimensional Anderson model with one open channel
We study the distribution of phases and of Wigner delay times for a
one-dimensional Anderson model with one open channel. Our approach, based on
classical Hamiltonian maps, allows us an analytical treatment. We find that the
distribution of phases depends drastically on the parameter where is the variance of the disorder distribution and
the wavevector. It undergoes a transition from uniformity to singular
behaviour as increases. The distribution of delay times shows
universal power law tails , while the short time behaviour is
- dependent.Comment: 4 pages, 2 figures, Submitted to PR