342 research outputs found
Delocalization of Wannier-Stark ladders by phonons: tunneling and stretched polarons
We study the coherent dynamics of a Holstein polaron in strong electric
fields. A detailed analytical and numerical analysis shows that even for small
hopping constant and weak electron-phonon interaction, polaron states can
become delocalized if a resonance condition develops between the original
Wannier-Stark states and the phonon modes, yielding both tunneling and
`stretched' polarons. The unusual stretched polarons are characterized by a
phonon cloud that {\em trails} the electron, instead of accompanying it. In
general, our novel approach allows us to show that the polaron spectrum has a
complex nearly-fractal structure, due to the coherent coupling between states
in the Cayley tree which describes the relevant Hilbert space. The eigenstates
of a finite ladder are analyzed in terms of the observable tunneling and
optical properties of the system.Comment: 7 pages, 4 figure
Aharanov-Bohm excitons at elevated temperatures in type-II ZnTe/ZnSe quantum dots
Optical emission from type-II ZnTe/ZnSe quantum dots demonstrates large and
persistent oscillations in both the peak energy and intensity indicating the
formation of coherently rotating states. Furthermore, the Aharanov-Bohm (AB)
effect is shown to be remarkably robust and persists until 180K. This is at
least one order of magnitude greater than the typical temperatures in
lithographically defined rings. To our knowledge this is the highest
temperature at which the AB effect has been observed in semiconductor
structures
Microwave-induced magnetotransport phenomena in two-dimensional electron systems: Importance of electrodynamic effects
We discuss possible origins of recently discovered microwave induced
photoresistance oscillations in very-high-electron-mobility two-dimensional
electron systems. We show that electrodynamic effects -- the radiative decay,
plasma oscillations, and retardation effects, -- are important under the
experimental conditions, and that their inclusion in the theory is essential
for understanding the discussed and related microwave induced magnetotransport
phenomena.Comment: 5 pages, including 2 figures and 1 tabl
Interaction quench dynamics in the Kondo model in presence of a local magnetic field
In this work we investigate the quench dynamics in the Kondo model on the
Toulouse line in presence of a local magnetic field. It is shown that this
setup can be realized by either applying the local magnetic field directly or
by preparing the system in a macroscopically spin-polarized initial state. In
the latter case, the magnetic field results from a subtlety in applying the
bosonization technique where terms that are usually referred to as finite-size
corrections become important in the present non-equilibrium setting. The
transient dynamics is studied by analyzing exact analytical results for the
local spin dynamics. The time scale for the relaxation of the local dynamical
quantities turns out to be exclusively determined by the Kondo scale. In the
transient regime, one observes damped oscillations in the local correlation
functions with a frequency set by the magnetic field.Comment: 8 pages, 2 figures; minor changes, version as publishe
Spin and energy transfer in nanocrystals without transport of charge
We describe a mechanism of spin transfer between individual quantum dots that
does not require tunneling. Incident circularly-polarized photons create
inter-band excitons with non-zero electron spin in the first quantum dot. When
the quantum-dot pair is properly designed, this excitation can be transferred
to the neighboring dot via the Coulomb interaction with either {\it
conservation} or {\it flipping} of the electron spin. The second dot can
radiate circularly-polarized photons at lower energy. Selection rules for spin
transfer are determined by the resonant conditions and by the strong spin-orbit
interaction in the valence band of nanocrystals. Coulomb-induced energy and
spin transfer in pairs and chains of dots can become very efficient under
resonant conditions. The electron can preserve its spin orientation even in
randomly-oriented nanocrystals.Comment: 13 pages, 3 figure
Wave Functions and Energies of Magnetopolarons in Semiconductor Quantum Wells
The classification of magnetopolarons in semiconductor quantum wells (QW) is
represented. Magnetopolarons appear due to the Johnson - Larsen effect. The
wave functions of usual and combined magnetopolarons are obtained by the
diodanalization of the Schrodinger equation.Comment: 7 pages, 2 figure
Robot-assisted technologies for targeted prostate biopsy: a literature review
One key aspect in treating any cancer is timely diagnosis and treatment. Obtaining the right diagnosis depends mainly on running the biopsy algorithm. Most studies show a significant increase in sensitivity and specificity in the targeted tissue sampling method compared to standard biopsy. The human factor can result in more medical errors. This can be solved by replacing the standard biopsy method with a more advanced one. The human factor is excluded from the biopsy sampling process using the semi-automatic robotic biopsy needle guidance. This paper presents a literature review development in robot assisted prostate biopsy. A literature review was performed using PubMed and Scopus databases. Papers reporting on experiments using semi-automatic robotic systems were included. Using the literature, we described the prerequisites for the development the software for semi-automatic targeted biopsy to increase the sensitivity and specificity of prostate cancer diagnosis
Nonlinear acousto-electric transport in a two-dimensional electron system
We study both theoretically and experimentally the nonlinear interaction
between an intense surface acoustic wave and a two-dimensional electron plasma
in semiconductor-piezocrystal hybrid structures. The experiments on hybrid
systems exhibit strongly nonlinear acousto-electric effects. The plasma turns
into moving electron stripes, the acousto-electric current reaches its maximum,
and the sound absorption strongly decreases. To describe the nonlinear
phenomena, we develop a coupled-amplitude method for a two-dimensional system
in the strongly nonlinear regime of interaction. At low electron densities the
absorption coefficient decreases with increasing sound intensity, whereas at
high electron density the absorption coefficient is not a monotonous function
of the sound intensity. High-harmonic generation coefficients as a function of
the sound intensity have a nontrivial behavior. Theory and experiment are found
to be in a good agreement.Comment: 27 pages, 6 figure
Kinetics of exciton photoluminescence in type-II semiconductor superlattices
The exciton decay rate at a rough interface in type-II semiconductor
superlattices is investigated. It is shown that the possibility of
recombination of indirect excitons at a plane interface essentially affects
kinetics of the exciton photoluminescence at a rough interface. This happens
because of strong correlation between the exciton recombination at the plane
interface and at the roughness. Expressions that relate the parameters of the
luminescence kinetics with statistical characteristics of the rough interface
are obtained. The mean height and length of roughnesses in GaAs/AlAs
superlattices are estimated from the experimental data.Comment: 3 PostScript figure
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