780 research outputs found
Atomic current in optical lattices: Esaki-Tsu equation revisited
The paper discusses the master equation approach to derivation of the
Esaki-Tsu equation for drift current. It is shown that the relaxation term in
the master equation can be identified by measuring the velocity distribution of
the carriers. We also show that the standard form of the relaxation term, used
earlier to derive Esaki-Tsu equation, predicts unphysical velocity distribution
and suggest a more elaborated relaxation term, which is argued to correctly
capture the effect of bosonic bath in experiments on atomic current in optical
lattices.Comment: 4 page
Photoassisted sequential resonant tunneling through superlattices
We have analyzed theoretically the photoassisted tunneling current through a
superlattice in the presence of an AC potential. For that purpose we have
developed a new model to calculate the sequential resonant currrent trhough a
superlattice based in the TRansfer Hamiltonian Method. The tunneling current
presents new features due to new effective tunneling chanels coming from the
photoside bands induced by the AC field. Our theoretical results are in good
agreement with the available experimental evidence.Comment: Revtex 3.0 4 pages, 4 figures uuencoded compressed tar-fil
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
Phonon-induced optical superlattice
We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments
Quantum Interference Phenomena in the Local Polarization Dynamics of Mesoscopic Systems: An NMR Observation
It was predicted that local spin polarization in a ring of five dipolar
coupled spins should present a particular fingerprint of quantum interferences
reflecting both the discrete and finite nature of the system [Phys. Rev. Lett.
75 (1995) 4310]. We report its observation for the proton system of a
(CH)Fe molecule using a rare C as {\it local probe}. Novel
high frequency (Hz) polarization oscillations appear because
incomplete C-H cross-polarization transfer {\it splits} the
polarization state, in a portion that wanders in the proton system and one that
remains in the C. They interfere with each other after rejoining.Comment: 12 pages, RevTex, 4 Figures available upon request, to appear in
Chemical Physics Letter
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.
Superlattice properties of carbon nanotubes in a transverse electric field
Electron motion in a (n,1) carbon nanotube is shown to correspond to a de
Broglie wave propagating along a helical line on the nanotube wall. This
helical motion leads to periodicity of the electron potential energy in the
presence of an electric field normal to the nanotube axis. The period of this
potential is proportional to the nanotube radius and is greater than the
interatomic distance in the nanotube. As a result, the behavior of an electron
in a (n,1) nanotube subject to a transverse electric field is similar to that
in a semiconductor superlattice. In particular, Bragg scattering of electrons
from the long-range periodic potential results in the opening of gaps in the
energy spectrum of the nanotube. Modification of the bandstructure is shown to
be significant for experimentally attainable electric fields, which raises the
possibility of applying this effect to novel nanoelectronic devices.Comment: 7 pages, 3 figure
Quantum scattering in one dimension
A self-contained discussion of nonrelativistic quantum scattering is
presented in the case of central potentials in one space dimension, which will
facilitate the understanding of the more complex scattering theory in two and
three dimensions. The present discussion illustrates in a simple way the
concept of partial-wave decomposition, phase shift, optical theorem and
effective-range expansion.Comment: 8 page
Transport of strong-coupling polarons in optical lattices
We study the transport of ultracold impurity atoms immersed in a
Bose-Einstein condensate (BEC) and trapped in a tight optical lattice. Within
the strong-coupling regime, we derive an extended Hubbard model describing the
dynamics of the impurities in terms of polarons, i.e. impurities dressed by a
coherent state of Bogoliubov phonons. Using a generalized master equation based
on this microscopic model we show that inelastic and dissipative phonon
scattering results in (i) a crossover from coherent to incoherent transport of
impurities with increasing BEC temperature and (ii) the emergence of a net
atomic current across a tilted optical lattice. The dependence of the atomic
current on the lattice tilt changes from ohmic conductance to negative
differential conductance within an experimentally accessible parameter regime.
This transition is accurately described by an Esaki-Tsu-type relation with the
effective relaxation time of the impurities as a temperature-dependent
parameter.Comment: 25 pages, 6 figure
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