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

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 $B$ 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 $B\neq 0$ 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 $B$.Comment: 27 pages, 11 figures. To be published in Phys. Rev.