7,928 research outputs found
Excitonic Mott transition in double quantum wells
We consider an electron-hole system in double quantum wells theoretically. We
demonstrate that there is a temperature interval over which an abrupt jump in
the value of the ionization degree occurs with an increase of the carrier
density or temperature. The opposite effect - the collapse of the ionized
electron-hole plasma into an insulating exciton system - should occur at lower
densities. In addition, we predict that under certain conditions there will be
a sharp decrease of the ionization degree with increasing temperature - the
anomalous Mott transition. We discuss how these effects could be observed
experimentally.Comment: 6 pages, 4 figure
Photocarrier escape time in quantum-well light-absorbing devices: Effects of electric field and well parameters
We analyze the dependence of the carrier escape time from a single-quantum-well optoelectronic device on the aplied electric field and well width and depth. For this purpose, a new simple and computationally efficient theory is developed. This theory is accurate in the case of electrons, and the assessment of the applicability for holes is given. Semi-analytical expressions for the,escape times are derived. Calculations are compared to experimental results and previous numerical simulations. Significant correlations between the Position,of quantum-well energy levels and the value of the escape time are found. the main escape mechanism At room temperature is established to be thermally assisted tunneling/emission through near-barrier-edge states. The formation of a new eigenstate in the near-barrier-edge energy region is found to reduce the electron escape time significantly, which can be used for practical device optimization
The Running BFKL: Resolution of Caldwell's Puzzle
The HERA data on the proton structure function, , at very small
and show the dramatic departure of the logarithmic slope, , from theoretical predictions based on the DGLAP
evolution. We show that the running BFKL approach provides the quantitative
explanation for the observed and/or -dependence of .Comment: 7 pages, Latex, 4 Figures, P
Quantum-well design for monolithic optical devices with gain and saturable absorber sections
We propose a new design of semiconductor quantum-well heterostructures, which can be used to improve the performance of monolithic mode-locked diode lasers and all-optical signal-processing devices with gain and saturable absorber sections. Numerical modeling shows that this design can increase the carrier sweep-out rate from the absorber section by several orders of magnitude, while retaining high carrier confinement on the ground level making for efficient signal amplification by the gain sections
Breaking of k_\perp-factorization for Single Jet Production off Nuclei
The linear k_\perp-factorization is part and parcel of the pQCD description
of high energy hard processes off free nucleons.
In the case of heavy nuclear targets the very concept of nuclear parton
density becomes ill-defined as exemplified by the recent derivation [2] of
nonlinear nuclear k_\perp-factorization for forward dijet production in DIS off
nuclei. Here we report a derivation of the related breaking of
k_\perp-factorization for single-jet processes. We present a general formalism
and apply it to several cases of practical interest: open charm and quark and
gluon jet production in the central to beam fragmentation region of
\gamma^*p,\gamma^*A, pp and pA collisions. We show how the pattern of
k_\perp-factorization breaking and the nature and number of exchanged nuclear
pomerons do change within the phase space of produced quark and gluon jets. As
an application of the nonlinear k_\perp-factorization we discuss the Cronin
effect. Our results are also applicable to the p_\perp-dependence of the
Landau-Pomeranchuk-Migdal effect for, and nuclear quenching of, jets produced
in the proton hemisphere of pA collisions.Comment: 55 pages, 9 eps figures, presentation shortened, a number of typos
removed, to appear in Phys. Rev.
Unitarity cutting rules for the nucleus excitation and topological cross sections in hard production off nuclei from nonlinear k_t-factorization
At the partonic level, a typical final state in small-x deep inelastic
scattering off nuclei and hard proton-nucleus collisions can be characterized
by the multiplicity of color-excited nucleons. Within reggeon field theory,
each color-excited nucleon is associated with the unitarity cut of the pomeron
exchanged between the projectile and nucleus. In this communication we derive
the unitarity rules for the multiplicity of excited nucleons, alias cut
pomerons, alias topological cross sections, for typical hard dijet production
processes. We demonstrate how the coupled-channel non-Abelian intranuclear
evolution of color dipoles, inherent to pQCD, gives rise to the reggeon field
theory diagrams for final states in terms of the uncut, and two kinds of cut,
pomerons. Upon the proper identification of the uncut and cut pomeron
exchanges, the topological cross sections for dijet production follow in a
straightforward way from the earlier derived nonlinear k_t - factorization
quadratures for the inclusive dijet cross sections. The concept of a coherent
(collective) nuclear glue proves extremely useful for the formulation of
reggeon field theory vertices of multipomeron - cut and uncut - couplings to
particles and between themselves. A departure of our unitarity cutting rules
from the ones suggested by the pre-QCD Abramovsky-Kancheli-Gribov rules, stems
from the coupled-channel features of intranuclear pQCD. We propose a
multiplicity re-summation as a tool for the isolation of topological cross
sections for single-jet production.Comment: 53 pages, 16 eps-figures, to appear in Phys. Rev.
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