1,188 research outputs found
Coulomb interaction signatures in self-assembled lateral quantum dot molecules
We use photoluminescence spectroscopy to investigate the ground state of
single self-assembled InGaAs lateral quantum dot molecules. We apply a voltage
along the growth direction that allows us to control the total charge occupancy
of the quantum dot molecule. Using a combination of computational modeling and
experimental analysis, we assign the observed discrete spectral lines to
specific charge distributions. We explain the dynamic processes that lead to
these charge configurations through electrical injection and optical
generation. Our systemic analysis provides evidence of inter-dot tunneling of
electrons as predicted in previous theoretical work.Comment: 9 pages, 4 figure
Electron and hole gas in modulation doped GaAs/AlGaAs radialheterojunctions
We perform self-consistent Schr\ua8
odinger-Poisson calculations with exchange and correlation corrections to
determine the electron and hole gas in a radial heterojunction formed in a GaAs/AlGaAs core-multi-shell nanowire, which is either n- or p-doped. We show that the electron and hole gases can be tuned to different localizations and symmetries inside the core as a function of the doping density/gate potential. Contrary to planar heterojunctions, conduction electrons do not form a uniform 2D electron gas (2DEG) localized at the GaAs/AlGaAs interface, but rather show a transition between an isotropic, cylindrical distribution deep in the GaAs core (low doping) and a set of six tunnel-coupled quasi-1D channels at the edges of the interface (high doping). Holes, on the other hand, are much more localized at the GaAs/AlGaAs interface. At low doping, they present an additional localization pattern with six separated 2DEGs strips. The field generated by a back-gate may easily deform the electron or hole gas, breaking the sixfold symmetry. Single 2DEGs at one interface or multiple quasi-1D channels are shown to form as a function of voltage intensity, polarity, and carrier type
Dielectric control of spin in semiconductor spherical quantum dots
The ground state electronic configuration of semiconductor spherical quantum dots populated with
different numbers of excess electrons, for different radii and dielectric constants of the embedding
medium is calculated and the corresponding phase diagram drawn. To this end, an extension of the
spin density functional theory to study systems with variable effective mass and dielectric constant
is employed. Our results show that high/low spin configurations can be switched by appropriate
changes in the quantum dot embedding environment and suggest the use of the quantum dot spin as
a sensor of the dielectric response of medi
Nitric oxide induces the alternative oxidase pathway in Arabidopsis seedlings deprived of inorganic phosphate
Phosphate starvation compromises electron fow through the cytochrome pathway of the mitochondrial electron transport chain, and plants commonly respond to phosphate deprivation by increasing fow through the alternative oxidase (AOX). To test whether this response is linked to the increase in nitric oxide (NO) production that also increases under phosphate starvation, Arabidopsis thaliana seedlings were grown for 15 d on media containing either 0 or 1 mM inorganic phosphate. The effects of the phosphate supply on growth, the production of NO, respiration, the AOX level and the production of superoxide were compared for wild-type (WT) seedlings and the nitrate reductase double mutant nia. Phosphate deprivation increased NO production in WT roots, and the AOX level and the capacity of the alternative pathway to consume electrons in WT seedlings; whereas the same treatment failed to stimulate NO production and AOX expression in the nia mutant, and the plants had an altered growth phenotype. The NO donor S-nitrosoglutathione rescued the growth phenotype of the nia mutants under phosphate deprivation to some extent, and it also increased the respiratory capacity of AOX. It is concluded that NO is required for the induction of the AOX pathway when seedlings are grown under phosphate-limiting conditions.This work was supported by research grants (AGL2010-16167; AGL2014-52396-P) from the Spanish Ministry of Economy and Competitiveness (MINECO) to JFM, an FPI fellowship from MINECO (BR), and a Marie Curie Intra-European Fellowship for Career Development within the 7th European Community Framework Programme (KJG and RGR).Peer Reviewe
Petrography and mineralogy of the white marble and black stone of Göktepe (Mugla, Turkey) used in antiquity: New data for provenance determination
The discovery near Göktepe (Mugla province, Western Turkey) of an ancient quarrying site of white marbles and black stones has recently been reported by some authors. Assigning the provenance of stone from ancient artifacts to Göktepe is currently possible mainly thanks to chemical, EPR and MGS data. Petrographic description, which many researchers use to characterize ancient marbles, is still incomplete. Several thin sections of both types of stone were thus examined in this study, and also used for cathodoluminescence analysis. As the rock is >99% calcite, trace minerals could only be detected in some samples by XRD analysis of insoluble residues after acetic acid attack. Data on strontium and manganese contents and carbon and oxygen isotopes were also recorded, for better understanding of some petrographic features. A new method of grain size characterization was tentatively introduced to improve the description of grain size variability in the white marble. Microstructure and grain size measurements on thin sections of this marble identify two petrographic varieties: the first is extremely fine with signs of dynamic recrystallization, and the second exhibits texture and MGS similar to those of Carrara marble. Statuary samples of white marble from Villa Adriana (Tivoli, Rome), preliminarily assigned in a previous study partly to Carrara and partly to Göktepe quarry, are reconsidered here. A certain degree of variability was found in the structures and textures in the thin sections of the Göktepe black stone. It may have undergone transformations at an advanced stage of diagenesis. One important source of this variability seems to be a fluid alteration event, revealed by both isotopic and chemical data and trace mineral assemblages
Isospin phases of vertically coupled double quantum rings under the influence of perpendicular magnetic fields
Vertically coupled double quantum rings submitted to a perpendicular magnetic
field are addressed within the local spin-density functional theory. We
describe the structure of quantum ring molecules containing up to 40 electrons
considering different inter-ring distances and intensities of the applied
magnetic field. When the rings are quantum mechanically strongly coupled, only
bonding states are occupied and the addition spectrum of the artificial
molecules resembles that of a single quantum ring, with some small differences
appearing as an effect of the magnetic field. Despite the latter has the
tendency to flatten the spectra, in the strong coupling limit some clear peaks
are still found even when that can be interpretated from the
single-particle energy levels analogously as at zero applied field, namely in
terms of closed-shell and Hund's-rule configurations. Increasing the inter-ring
distance, the occupation of the first antibonding orbitals washes out such
structures and the addition spectra become flatter and irregular. In the weak
coupling regime, numerous isospin oscillations are found as a function of .Comment: 27 pages, 11 figures. To be published in Phys. Rev.
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