Applications of semiconductor nanocrystals such as biomarkers and light-emitting optoelectronic devices require that their fluorescence quantum yield be close to 100%. However, such quantum yields ...have not been obtained yet, in part, because non-radiative Auger recombination in charged nanocrystals could not be suppressed completely. Here, we synthesize colloidal core/thick-shell CdSe/CdS nanocrystals with 100% quantum yield and completely quenched Auger processes at low temperatures, although the nanocrystals are negatively photocharged. Single particle and ensemble spectroscopy in the temperature range 30-300 K shows that the non-radiative Auger recombination is thermally activated around 200 K. Experimental results are well described by a model suggesting a temperature-dependent delocalization of one of the trion electrons from the CdSe core and enhanced Auger recombination at the abrupt CdS outer surface. These results point to a route for the design of core/shell structures with 100% quantum yield at room temperature.
Full text
Available for:
IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic ...train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
.
The sums over (
e
,
e′
) spectra of
6
Li and
7
Li nuclei which correspond to the longitudinal sum rule are studied. It is suggested that due to the cluster structure of the lithium isotopes these ...sums may approximately be expressed in terms of such a sum pertaining to the
-particle. Calculation of these sums is performed in the framework of cluster models with antisymmetrization done with respect to all the nucleons. At momentum transfers higher than 0.8 fm
-1
the relations expressing the
A
= 6 or 7 sum in terms of the
A
= 4 sum prove to be valid with rather high accuracy. In the region of momentum transfers around 1 fm
-1
the longitudinal correlation functions of
6
Li and
7
Li nuclei are found to be close to that of the
-particle. Basing on this, the difference between the
q
values at which the high-
q
limit of the inelastic sum rule is reached in the
6, 7
Li cases and the
4
He case is explained. The experimental longitudinal sums in the range between 0.450 and 1.625 fm
-1
are employed to perform comparison with the theoretical sum rule calculated in the framework of cluster models. Out of the experimental sums, those in the range between 0.750 and 1.000 fm
-1
in the
6
Li case and between 0.750 and 1.125 fm
-1
in the
7
Li case are obtained in the present work. In the
6
Li case a complete agreement between experiment and the calculated sum rule is found while in the
7
Li case an agreement only at a qualitative level is observed.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In the Standard Solar Model a central role in the nucleosynthesis is played by reactions of the kind , which enter the proton-proton chains. These reactions can also be studied through the inverse ...photodisintegration reaction. One option is to use the Lorentz Integral Transform approach, which transforms the continuum problem into a bound state-like one. A way to check the reliability of such methods is a direct calculation, for example using the Kohn Variational Principle to obtain the scattering wave function and then directly calculate the response function of the reaction.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
An approach aimed to extend the applicability range of the nonrelativistic microscopic calculations of electronuclear response functions is reviewed. In the quasielastic peak region these ...calculations agree with experiment at momentum transfers up to about 0.4 GeV/
c
, while at higher momentum transfers being beyond 1 GeV/
c
a disagreement is seen. In view of this, a reference frame where dynamic relativistic corrections are small was employed to calculate the response functions and the results were transformed exactly to the laboratory reference frame. This proved to remove the major part of the disagreement with experiment. All leading-order relativistic corrections to the transition charge operator and to the one-body part of the transition current operator were taken into account in the calculations. Furthermore, a particular model to determine the kinematical inputs of the nonrelativistic calculations was introduced. This model provides the correct relativistic relationship between the reaction final-state energy and the momenta of the knocked-out nucleon and the residual system. The above-mentioned choice of a reference frame in conjunction with this model has led to an even better agreement with experiment.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A method to calculate reactions in quantum mechanics is outlined. It is advantageous, in particular, in problems with many open channels of various nature, i.e., when energy is not low. In the ...difference with more conventional approaches the dynamics calculations to be performed are bound-state type-calculations. Continuum spectrum states never enter the game. In the course of calculations there is no need to consider reaction channels, as well as reaction thresholds. Reaction channels and thresholds come into play at merely the kinematics level and only after a dynamics calculation is done.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The bra-ket formalism is generally applied to carry out representation-free considerations in quantum mechanics. It provides efficient means for this purpose, but at the same time, drawbacks are ...inherent in it. Some of these originate from the fact that the bra-ket notation is not suitable to handle the domains of the definitions of operators involved. An additional drawback is that the bra-ket formalism, being a dual-space formalism, excludes the natural one-space point of view. In the present work, a concise representation-free scheme is constructed. This scheme has no drawbacks of the bra-ket formalism. At the same time, this scheme provides the efficient means to carry out quantum mechanical considerations, such as all those offered by the bra-ket scheme. The present scheme allows both the one-space and dual-space interpretations, in contrast to the bra-ket scheme. Before the above, the strengths and drawbacks of the bra-ket formalism are addressed.
The Lorentz integral transform method is briefly reviewed. The issue of the inversion of the transform, and in particular its ill-posedness, is addressed. It is pointed out that the mathematical term
...ill-posed
is misleading and merely due to a historical misconception. In this connection standard regularization procedures for the solution of the integral transform problem are presented. In particular a recent one is considered in detail and critical comments on it are provided. In addition a general remark concerning the concept of the Lorentz integral transform as a method with a
controlled resolution
is made.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the net charge from positive to neutral to negative with a charge-tunable ...heterostructure. Negative photoluminescence polarization memory is enhanced by optical pumping of ground state electron spins, which we prove with the first measurements of the Hanle effect on an individual quantum dot. We use the Overhauser effect in a high longitudinal magnetic field to demonstrate efficient optical pumping of nuclear spins for all three charge states of the quantum dot.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
PDF
