853 research outputs found
Superlattice Structures of Graphene based Nanoribbons
Based on first-principles calculations we predict that periodically repeated
junctions of armchair graphene nanoribbons of different widths form
superlattice structures. In these superlattice heterostructures the width and
the energy gap are modulated in real space and specific states are confined in
certain segments. Orientation of constituent nanoribbons, their width and
length, the symmetry of the junction are the structural parameters to engineer
electronic properties of these quantum structures. Not only the size
modulation, but also composition modulation, such as periodically repeated,
commensurate heterojunctions of BN and graphene honeycomb nanoribbons result in
a multiple quantum well structure. We showed that these graphene based quantum
structures can introduce novel concepts to design nanodevices.Comment: amended versio
Bloch Oscillation under a Bichromatic Laser: Quasi-Miniband Formation, Collapse, and Dynamical Delocalization and Localization
A novel DC and AC driving configuration is proposed for semiconductor
superlattices, in which the THz AC driving is provided by an intense
bichromatic cw laser. The two components of the laser, usually in the visible
light range, are near but not exactly resonant with interband Wannier-Stark
transitions, and their frequency difference equals the Wannier-Stark ladder
spacing. Multi-photon processes with the intermediate states in the conduction
(valence) band cause dynamical delocalization and localization of valence
(conduction) electrons, and the corresponding formation and collapse of the
quasi-minibands.Comment: 4 pages, 3 figure
Real time Power Capping with Smart Circuit Breaker to maximize Power Utilization of Local Generator
Effective energy management and control is an
important and urgent issue in the emerging and developing
countries, so as to achieve their sustainable growth, because of
poor quality of power supply by their electric power companies.
In order to come up with the frequent electric power outage
by the power company, most of buildings in developing and
emerging countries install a power generator. Although because of
poor control system in the premises, utilization factor of output
capability of power generators is typically low except at peak
periods. To improve the utilization factor of power generator,
we propose a system, which can manage power segments in the
building using SCB (Smart Circuit Breaker). SCBs are connected
by wireless technologies with battery backup, and set their power
capping based on the indication issued by central manager. The
central manager computes power capping threshold of each SCB
using the proposed algorithm, in real-time fashion. Experimental
results show that the proposed algorithm can optimize the
required capacity of the local power generator and that we need
a feedback-looped adaptive threshold calculation algorithm
Large deformation analysis of ground with wall movement or hallow foundation under extremely low confining pressure using PIV
Large-scale natural disasters have occurred frequently in recent years. In such disasters, large ground deformation has been a recurring phenomenon. As it directly affects the structure, has dureable design is necessitated to minimize the damages. Additionally, the fracture process zones are predicted using numerical analysis, and thereafter, the results of the analysis are validated after comparison with the experimental ones. In this study, image analysis is performed using particle image velocimetry (PIV), and subsequently, the analysis results are validated by the comparison. We herein aim to improve the precision of the image-analysis results, and examine the experimental or analytical condition of reproducing the deformation
Symmetry-breaking and chaos in electron transport in semiconductor superlattices
We study the motion of electrons in a single miniband of a semiconductor
superlattice driven by THz electric field polarized along the growth direction.
We work in the semiclassical balance-equation model, including different
elastic and inelastic scattering rates, and incorporating the self-consistent
electric field generated by electron motion. We explore regions of complex
dynamics, which can include chaotic behaviour and symmetry-breaking. We
estimate the magnitudes of dc current and dc voltage that spontaneously appear
in regions of broken-symmetry for parameters characteristic of modern
semiconductor superlattices. This work complements PRL 80(1998)2669 [
cond-mat/9709026 ].Comment: 4 pages, 3 figures, RevTEX, EPS
Transient response of a quantum wave to an instantaneous potential step switching
The transient response of a stationary state of a quantum particle in a step
potential to an instantaneous change in the step height (a simplified model for
a sudden bias switch in an electronic semiconductor device) is solved exactly
by means of a semianalytical expression. The characteristic times for the
transient process up to the new stationary state are identified. A comparison
is made between the exact results and an approximate method.Comment: 8 pages, 8 figures, Revtex
Effect of nonlinearity on the dynamics of a particle in dc field-induced systems
Dynamics of a particle in a perfect chain with one nonlinear impurity and in
a perfect nonlinear chain under the action of dc field is studied numerically.
The nonlinearity appears due to the coupling of the electronic motion to
optical oscillators which are treated in adiabatic approximation.
We study for both the low and high values of field strength. Three different
range of nonlinearity is obtained where the dynamics is different. In low and
intermediate range of nonlinearity, it reduces the localization. In fact in the
intermediate range subdiffusive behavior in the perfect nonlinear chain is
obtained for a long time. In all the cases a critical value of nonlinear
strength exists where self-trapping transition takes place. This critical value
depends on the system and the field strength. Beyond the self-trapping
transition nonlinearity enhances the localization.Comment: 9 pages, Revtex, 6 ps figures include
Bloch oscillations, Zener tunneling and Wannier-Stark ladders in the time-domain
We present a time-domain analysis of carrier dynamics in a semiconductor
superlattice with two minibands. Integration of the density-matrix equations of
motion reveals a number of new features: (i) for certain values of the applied
static electric field strong interband transitions occur; (ii) in static fields
the complex time-dependence of the density-matrix displays a sequence of stable
plateaus in the low field regime, and (iii) for applied fields with a periodic
time-dependence the dynamic response can be understood in terms of the
quasienergy spectra.Comment: 4 pages, 6 PostScript figures available from [email protected], REVTEX
3.
Superlattice Magnetophonon Resonances in Strongly Coupled InAs/GaSb Superlattices
We report an experimental study of miniband magnetoconduction in
semiconducting InAs/GaSb superlattices. For samples with miniband widths below
the longitudinal optical phonon energy we identify a new superlattice
magnetophonon resonance (SLMPR) caused by resonant scattering of electrons
across the mini-Brillouin zone. This new resonant feature arises directly from
the drift velocity characteristics of the superlattice dispersion and total
magnetic quantisation of the superlattice Landau level minibands.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
Dynamics of Electric Field Domains and Oscillations of the Photocurrent in a Simple Superlattice Model
A discrete model is introduced to account for the time-periodic oscillations
of the photocurrent in a superlattice observed by Kwok et al, in an undoped 40
period AlAs/GaAs superlattice. Basic ingredients are an effective negative
differential resistance due to the sequential resonant tunneling of the
photoexcited carriers through the potential barriers, and a rate equation for
the holes that incorporates photogeneration and recombination. The
photoexciting laser acts as a damping factor ending the oscillations when its
power is large enough. The model explains: (i) the known oscillatory static I-V
characteristic curve through the formation of a domain wall connecting high and
low electric field domains, and (ii) the photocurrent and photoluminescence
time-dependent oscillations after the domain wall is formed. In our model, they
arise from the combined motion of the wall and the shift of the values of the
electric field at the domains. Up to a certain value of the photoexcitation,
the non-uniform field profile with two domains turns out to be metastable:
after the photocurrent oscillations have ceased, the field profile slowly
relaxes toward the uniform stationary solution (which is reached on a much
longer time scale). Multiple stability of stationary states and hysteresis are
also found. An interpretation of the oscillations in the photoluminescence
spectrum is also given.Comment: 34 pages, REVTeX 3.0, 10 figures upon request, MA/UC3M/07/9
- …