A light-hole exciton is a quasiparticle formed from a single electron bound to a single light hole. This type of fundamental excitation, if confined inside a semiconductor quantum dot, could be ...advantageous in quantum information science and technology. However, it has been difficult to access it so far, because confinement and strain in conventional quantum dots favour a ground-state single-particle hole with a predominantly heavy-hole character. Here we demonstrate the creation of a light-hole exciton ground state by applying elastic stress to an initially unstrained quantum dot. Its signature is clearly distinct from that of the well-known heavy-hole exciton and consists of three orthogonally polarized bright optical transitions and a fine-structure splitting of hundreds of microelectronvolts between in-plane and out-of-plane components. This work paves the way for the exploration of the fundamental properties and of the potential relevance of three-dimensionally confined light-hole states in quantum technologies.
We study the effect of an external biaxial stress on the light emission of single InGaAs/GaAs(001) quantum dots placed onto piezoelectric actuators. With increasing compression, the emission ...blueshifts and the binding energies of the positive trion (X+) and biexciton (XX) relative to the neutral exciton (X) show a monotonic increase. This phenomenon is mainly ascribed to changes in electron and hole localization and it provides a robust method to achieve color coincidence in the emission of X and XX, which is a prerequisite for the possible generation of entangled photon pairs via the recently proposed "time reordering" scheme.
The objective of this investigation was to determine the effect of technology on attention and achievement within a classroom context, taking motivation and concentration into account as well. ...Lessons in Geography, English and Mathematics were presented to an experimental and a control group consisting of 23 and 22 Grade 8 learners, respectively. Technology was implemented for the experimental group but not for the control group. Significant differences were found between the average achievements of a group of learners, exposed to technology during a lesson, compared to a group not exposed to technology. Significant differences were also found between the average attention of a group of learners, exposed to technology during a lesson, compared to a group not exposed to technology. A high positive relationship was obtained between motivation and concentration and moderate to high positive correlations were obtained between attention, concentration and motivation, taken jointly as independent variables and achievement as the dependent variable.
The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), and its associated pathogen “Candidatus Liberibacter solanacearum” (Ca. L. solanacearum), the putative causal agent of zebra ...chip (ZC) disease in potatoes (Solanum tuberosum L.), were sampled in commercial potato fields and untreated control plots for 3 yr in multiple locations in Texas, Kansas, Nebraska, and Colorado. Populations of the potato psyllid varied across years and across potato growing regions. However, the percentage of potato psyllids infected with Ca. L. solanacearum although variable across years, was consistently highest in the Lower Rio Grande Valley of Texas (LRGV), the reported overwintering location for this pest. The numbers of Ca. L. solanacearum—infected psyllids collected on field traps and large nymphs counted on leaf samples were both positively correlated with the final percentage of ZC in tubers. In the LRGV, where vector and disease pressure is the highest, population levels of immature life stages of the psyllid and percentage of ZC differed greatly between commercial and untreated fields. These results show that the pest management program that was used can be effective at controlling development of the psyllid and ultimately reducing the incidence of ZC.
Coulomb interactions between electrons lead to the observed multiplet structure and breakdown of the Aufbau principle for atomic d and f shells. Nevertheless, these effects can disappear in extended ...systems. For instance, the multiplet structure of atomic carbon is not a feature of graphite or diamond. A quantum dot is an extended system containing ∼106 atoms for which electron-electron interactions do survive and the interplay between the Coulomb energy, J, and the quantization energy, ΔE, is crucial to Coulomb blockade. We have discovered consequences of Coulomb interactions in self-assembled quantum dots by interpreting experimental spectra with an atomistic calculation. The Coulomb effects, evident in the photon emission process, are tunable in situ by controlling the quantum dot charge from +6e to −6e. The same dot shows two regimes: J≤ΔE for electron charging yet J ΔE for hole charging. We find a breakdown of the Aufbau principle for holes; clear proof of non-perturbative hole-hole interactions; promotion-demotion processes in the final state of the emission process, effects first predicted a decade ago; and pronounced configuration hybridizations in the initial state. The level of charge control and the energy scales result in Coulomb effects with no obvious analogues in atomic physics.
We derive an analytic connection between the screened self-consistent effective potential from density-functional theory (DFT) and atomic effective pseudopotentials (AEPs). The motivation to derive ...AEPs is to address structures with thousands to hundreds of thousands of atoms, as given in most nanostructures. The use of AEPs allows us to bypass a self-consistent procedure and to address eigenstates around a certain region of the spectrum (e.g., around the band gap). The bulk AEP construction requires two simple DFT calculations of slightly deformed elongated cells. The ensuing AEPs are given on a fine reciprocal space grid, including the small reciprocal vector components, are free of adjustable parameters, and involve no fitting procedure. We further show how to connect the AEPs of different bulk materials, which is necessary to obtain accurate band offsets. We derive a total of 20 AEPs for group-III-V, II-VI, and IV semiconductors and demonstrate their accuracy and transferability by comparison to DFT calculations of strained bulk structures, quantum wells with varying thickness, and semiconductor alloys.
Imaginary audience, personal fable, and over-estimation of responsibilities are typical characteristics of egocentric behaviour during adolescence. The aim of the research was to establish how these ...egocentric characteristics manifest themselves in a learning context. An empirical investigation was carried out involving 316 learners from Grade 8 to 12. A questionnaire was adapted to measure egocentrism in a learning context. Significant negative correlations were found between academic achievement and egocentrism in a learning context. It is possible that as much as 17% of the variance in academic achievement can be explained by the egocentric behaviour of adolescents. No gender differences could be established. From the results it can be concluded that Grade 12 learners are more inclined to egocentric behaviour in a learning context compared to learners in Grade 8 and 9.
Within the scheme of the large-scale atomic effective pseudopotential program (LATEPP), the Schrodinger equation of an electronic system is solved within an effective single-particle approach. ...Although not limited to, it focuses on the recently introduced atomic effective pseudopotentials derived from screened local effective crystal potentials as obtained from self-consistent density functional theory calculations. The problem can be solved in both real (real-space grid) and reciprocal space (plane-wave basis functions). Following the idea of atomic effective pseudopotentials, the density, and hence a self-consistent cycle, is not required and not implemented. An iterative solver is implemented to deliver the eigenstates close to a selected reference energy, e.g., around the band gap of a semiconductor. This approach is particularly well suited for theoretical investigations of the electronic structure of semiconductor nanostructures and we demonstrate linear scaling with the system size up to around 100 000 atoms on a single standard compute node. Moreover, an efficient real-space treatment of spin-orbit coupling within the pseudopotential framework is proposed in this work allowing for a fully relativistic description.
•Calculation of two impurities two electron states using LCAO-MO method.•Explored energy splitting and exchange times in singlet–triplet states.•Control of singlet–triplet state populations via Rabi ...frequency adjustments.•Dynamics of Mollow triplet spectrum as a function of detuning.
The current study uses various computational methods to determine the eigenvalues and eigenvectors of a specific system—namely, a two-impurity, two-electron system within a dumbbell-shaped quantum dot. Initially, the single-electron, single-impurity problem is resolved using the effective mass approximation and the finite element method. Subsequently, a technique similar to the linear combination of atomic orbitals is applied to derive singlet–triplet states. The research work deeply investigates the key characteristics of the mentioned states, with a particular focus on their energy splitting and exchange times. Additionally, it highlights the dynamic evolution of the singlet–triplet two-level system, illustrating its manipulation through detuning and Rabi frequency. The Mollow triplet spectrum is also calculated and analyzed under various initial conditions. The findings of this research have significant implications across multiple domains, including the advancement of quantum information processing, the enhancement of optoelectronic device performance, and the development of innovative sensing and communication technologies.
Long-term sustainable management of zebra chip (ZC) disease of potato requires development of tolerant or resistant germplasm. To this end, 283 potato varieties and breeding clones were infected with ...the ZC putative causal agent 'Candidatus Liberibacter solanacearum' (Lso) by potato psyllid vector inoculations in 2010, 2011, 2012, and 2013. Potato germplasm was then examined for development of fresh and fried ZC symptoms. Over multiple years 29 breeding clones exhibited little to no symptoms in freshly cut tuber slices, and five exhibited little to no symptoms in fried slices. These five presumed tolerant breeding clones were chosen for further screening to determine whether the lack of physiological responses to Lso infection was the cause of observed tolerance. To this end, tuber amino acid, sugar, and phenolic levels were compared between noninfected and Lso-infected plants. The five putative tolerant clones had less dramatic shifts in host physiology following Lso infection than the susceptible Atlantic cultivar. This suggested lack of host responses to Lso infection that result in major changes in tuber biochemistry is a potential mechanism of ZC resistance. However, the susceptible Atlantic cultivar did have consistently greater Lso titers compared with two of the tolerant entries, so for these reductions in Lso pathogen progression also might be a factor. Regardless, lack of host responses could still remain one trait that could be used to aid in selection of ZC-resistant potato varieties, as other tolerant lines had infection levels consistent with susceptible Atlantic cultivar. These results also suggest that germplasm derived from relatives of cultivated potato plants are viable sources of ZC disease resistance.
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