2,313 research outputs found
Paramagnetic-diamagnetic interplay in quantum dots for non-zero temperatures
In the usual Fock-and Darwin-formalism with parabolic potential characterized
by the confining energy \eps_o := \hbar\omega_o= 3.37 meV, but including
explicitly also the Zeeman coupling between spin and magnetic field, we study
the combined orbital and spin magnetic properties of quantum dots in a
two-dimensional electron gas with parameters for GaAs, for N =1 and N >> 1
electrons on the dot.
For N=1 the magnetization M(T,B) consists of a paramagnetic spin contribution
and a diamagnetic orbital contribution, which dominate in a non-trivial way at
low temperature and fields rsp. high temperature and fields.
For N >> 1, where orbital and spin effects are intrinsically coupled in a
subtle way and cannot be separated, we find in a simplified Hartree
approximation that at N=m^2, i.e. at a half-filled last shell, M(T,B,N) is
parallel (antiparallel) to the magnetic field, if temperatures and fields are
low enough (high enough), whereas for N\ne m^2 the magnetization oscillates
with B and N as a T-dependent periodic function of the variable
x:=\sqrt{N}eB/(2m^*c\omega_o), with T-independent period \Delta x =1 (where m^*
:= 0.067 m_o is the small effective mass of GaAs, while m_o is the electron
mass). Correspondingly, by an adiabatic demagnetization process, which should
only be fast enough with respect to the slow transient time of the magnetic
properties of the dot, the temperature of the dot diminishes rsp. increases
with decreasing magnetic field, and in some cases we obtain quite pronounced
effects.Comment: LaTeX, 28 pages; including three .eps-figures; final version accepted
by J. Phys. CM, with minimal changes w.r.to v
Suppression of electron relaxation and dephasing rates in quantum dots caused by external magnetic fields
An external magnetic field has been applied in laterally coupled dots (QDs)
and we have studied the QD properties related to charge decoherence. The
significance of the applied magnetic field to the suppression of
electron-phonon relaxation and dephasing rates has been explored. The coupled
QDs have been studied by varing the magnetic field and the interdot distance as
other system parameters. Our numerical results show that the electron
scattering rates are strongly dependent on the applied external magnetic field
and the details of the double QD configuration.Comment: 13 pages, 6 figure
Rashba-control for the spin excitation of a fully spin polarized vertical quantum dot
Far infrared radiation absorption of a quantum dot with few electrons in an
orthogonal magnetic field could monitor the crossover to the fully spin
polarized state. A Rashba spin-orbit coupling can tune the energy and the spin
density of the first excited state which has a spin texture carrying one extra
unit of angular momentum. The spin orbit coupling can squeeze a flipped spin
density at the center of the dot and can increase the gap in the spectrum.Comment: 4 pages, 5 figure
Measurement of complex fragments and clues to the entropy production from 42-137-MeV/nucleon Ar + Au
Intermediate-rapidity fragments with A=1-14 emitted from 42-137-MeV/nucleon Ar + Au have been measured. Evidence is presented that these fragments arise from a common moving source. Entropy values are extracted from the mass distributions by use of quantum statistical and Hauser-Feshbach theories. The extracted entropy values of S/A≈2-2.4 are much smaller than the values expected from measured deuteron-to-proton ratios, but are still considerably higher than theoretically predicted values
Light particle spectra from 35 MeV/nucleon 12C-induced reactions on 197Au
Energy spectra for p, d, t, 3He, 4He, and 6He from the reaction 12C+197Au at 35 MeV/nucleon are presented. A common intermediate rapidity source is identified using a moving source fit to the spectra that yields cross sections which are compared to analogous data at other bombarding energies and to several different models. The excitation function of the composite to proton ratios is compared with quantum statistical, hydrodynamic, and thermal models
A Comment on Conical Flow Induced by Heavy-Quark Jets
The suppression of high transverse momentum particles, recently discovered at
RHIC, is commonly interpreted as due to parton energy loss. In high energy
nuclear collisions, QCD jets would deposit a large fraction of their energy and
into the produced matter. The question of how this energy is degraded and
whether we can use this phenomenon to probe the properties of the produced
matter is now under active discussion. It has been proposed that if this
matter, which is now being referred to as a {\em strongly coupled Quark-Gluon
Plasma} (sQGP), may behave as a liquid with a very small viscosity.
In this case, a very specific collective excitation should be produced,
called the ``conical flow'', similar e.g. to the sonic booms generated by the
shock waves produced by supersonic planes. The RHIC experiments seem indeed to
be obtaining some indication that the production of particles emitted opposite
to a high- jet may actually be peaked away from the quenched jet
direction, at an angle roughly consistent with the direction expected in case a
shock wave is produced (i.e. orthogonal to the Mach cone). In this note we
speculate that for tagged heavy-quark jets one may observe a shrinkage of the
Mach cone at moderate . The experimental observation of such an effect
would be a very good test for the validity of the whole picture currently
emerging from the study of partonic matter in nuclear collisions
Quantum thermodynamics of a charged magneto-oscillator coupled to a heat bath
Explicit results for various quantum thermodynamic function (QTF) of a
charged magneto-oscillator coupled to a heat bath at arbitrary temperature are
demonstrated in this paper. Discernible expressions for different QTF in the
two limits of very low and very high temperatures are presented for three
popular heat bath models : Ohmic, single relaxation time and blackbody
radiation. The central result is that the effect of magnetic field turns out to
be important at low temperatures yet crucial at high temperatures. It is
observed that the dissipation parameter, , and the cyclotron frequency,
, affect the decaying or rising behaviour of various QTF in just the
opposite way to each other at low temperatures. In the high temperature regime,
the effect of is much pronounced than that of .Comment: 26 Pages, 18 Figure
Comparative Analysis of the Mechanisms of Fast Light Particle Formation in Nucleus-Nucleus Collisions at Low and Intermediate Energies
The dynamics and the mechanisms of preequilibrium-light-particle formation in
nucleus-nucleus collisions at low and intermediate energies are studied on the
basis of a classical four-body model. The angular and energy distributions of
light particles from such processes are calculated. It is found that, at
energies below 50 MeV per nucleon, the hardest section of the energy spectrum
is formed owing to the acceleration of light particles from the target by the
mean field of the projectile nucleus. Good agreement with available
experimental data is obtained.Comment: 23 pages, 10 figures, LaTeX, published in Physics of Atomic Nuclei
v.65, No. 8, 2002, pp. 1459 - 1473 translated from Yadernaya Fizika v. 65,
No. 8, 2002, pp. 1494 - 150
Two-Particle Correlations in Relativistic Heavy-Ion Collisions
Two-particle momentum correlations between pairs of identical particles
produced in relativistic heavy-ion reactions can be analyzed to extract the
space-time structure of the collision fireball. We review recent progress in
the application of this method, based on newly developed theoretical tools and
new high-quality data from heavy-ion collision experiments. Implications for
our understanding of the collision dynamics and for the search for the
quark-gluon plasma are discussed.Comment: 44 pages, LaTeX, 11 Figures, uses special style files (included),
prepared for Ann. Rev. Nucl. Part. Sci. 49 (1999). Error in Chapt. 1
corrected and a few references adde
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