Fano effect and Kondo effect in quantum dots formed in strongly coupled quantum wells

We present lateral transport measurements on strongly, vertically coupled quantum dots formed in separate quantum wells in a GaAs/AlGaAs heterostructure. Coulomb oscillations are observed forming a honeycomb lattice consistent with two strongly coupled dots. When the tunnel barriers in the upper well are reduced we observe the Fano effect due to the interfering paths through a resonant state in the lower well and a continuum state in the upper well. In both regimes an in plane magnetic field reduces the coupling between the wells when the magnetic length is comparable to the center to center separation of the wells. We also observe the Kondo effect which allows the spin states of the double dot system to be probed.Comment: 4 pages, 5 figure

Spectroscopy of orbital ordering in La0.5Sr1.5MnO4 : A many-body cluster calculation

We have studied the orbital ordering (OO) in La0.5Sr1.5MnO4 and its soft x-ray resonant diffraction spectroscopic signature at the Mn L2, L3 edges. We have modelled the system in second quantization as a small planar cluster consisting of a central Mn atom, with the first neighbouring shells of oxygen and Mn atoms. For the effective Hamiltonian we consider Slater-Koster parameters, charge transfer and electron correlation energies obtained from previous measurements on manganites. We calculate the OO as a function of oxygen distortion and spin correlation used as adjustable parameters. Their contribution as a function of temperature is clearly distinguished with a good spectroscopic agreement.Comment: 5 pages 3 figure

Study Protocol for a Cluster-Randomized Trial of a Bundle of Implementation Support Strategies to Improve the Fidelity of Implementation of Schoolwide Positive Behavioral Interventions and Supports in Rural Schools

Background: Improving the implementation of evidence-based interventions is important for population-level impacts. Positive Behavioral Interventions and Supports (PBIS) is effective for improving school climate and students’ behavioral outcomes, but rural schools often lag behind urban and suburban schools in implementing such initiatives. Methods/Design: This paper describes a Type 3 hybrid implementation-effectiveness trial of Rural School Support Strategies (RS3), a bundle of implementation support strategies selected to improve implementation outcomes in rural schools. In this two-arm parallel group trial, 40 rural public schools are randomized to receive: 1) a series of trainings about PBIS; or 2) an enhanced condition with training plus RS3. The trial was planned for two years, but due to the pandemic has been extended another year. RS3 draws from the Interactive Systems Framework, with a university-based team (support system) that works with a team at each school (school-based delivery system), increasing engagement through strategies such as: providing technical assistance, facilitating school team functioning, and educating implementers. The primary organizational-level outcome is fidelity of implementation, with additional implementation outcomes of feasibility, acceptability, appropriateness, and cost. Staff-level outcomes include perceived climate and self-reported adoption of PBIS core components. Student-level outcomes include disciplinary referrals, academic achievement, and perceived climate. Mediators being evaluated include organizational readiness, school team functioning, and psychological safety. Discussion: The study tests implementation strategies, with strengths including a theory-based design, mixed methods data collection, and consideration of mediational mechanisms. Results will yield knowledge about how to improve implementation of universal prevention initiatives in rural schools

The nature of teachers' qualitative judgements: A matter of context and salience. Part Two: Out-of-context judgements

This second paper also takes up the issue of how teachers make judgements of primary students' writing. Once again, we examine the evidence base used by two teachers in their judgements, using qualitative techniques for mapping the inter-relationships among the indexes that teachers rely on to formulate judgements. Of special interest in this paper is how the teachers enacted judgements of student writing in the absence of knowledge about the institutional and pedagogical settings in which the writing had been produced, and also without knowledge of the student writer. The authors recommend that readers consider the discussion and findings offered in this paper in conjunction with paper one which precedes it

Density functional theory calculations of defect energies using supercells

Reliable calculations of defect properties may be obtained with density functional theory using the supercell approximation. We systematically review the known sources of error and suggest how to perform calculations of defect properties in order to minimize errors. We argue that any analytical error-correction scheme relying on electrostatic considerations is not appropriate to derive reliable defect formation energies, especially not for relaxed geometries. Instead we propose finite size scaling of the calculated defect formation energies, and compare the use of this with both fully converged and "Gamma" (Γ) point only k-point integration. We give a recipe for practical DFT calculations which will help to obtain reliable defect formation energies and demonstrate it using examples from III-V semiconductors

Single and Many Particle Correlation Functions and Uniform Phase Bases for Strongly Correlated Systems

The need for suitable many or infinite fermion correlation functions to describe some low dimensional strongly correlated systems is discussed. This is linked to the need for a correlated basis, in which the ground state may be postive definite, and in which single particle correlations may suffice. A particular trial basis is proposed, and applied to a certain quasi-1D model. The model is a strip of the 2D square lattice wrapped around a cylinder, and is related to the ladder geometries, but with periodic instead of open boundary conditions along the edges. Analysis involves a novel mean-field approach and exact diagonalisation. The model has a paramagnetic region and a Nagaoka ferromagnetic region. The proposed basis is well suited to the model, and single particle correlations in it have power law decay for the paramagnet, where the charge motion is qualitatively hard core bosonic. The mean field also leads to a BCS-type model with single particle long range order.Comment: 23 pages, in plain tex, 12 Postscript figures included. Accepted for publication in J.Physics : Condensed Matte

Giant Thermoelectric Effect from Transmission Supernodes

We predict an enormous order-dependent quantum enhancement of thermoelectric effects in the vicinity of a higher-order `supernode' in the transmission spectrum of a nanoscale junction. Single-molecule junctions based on 3,3'-biphenyl and polyphenyl ether (PPE) are investigated in detail. The nonequilibrium thermodynamic efficiency and power output of a thermoelectric heat engine based on a 1,3-benzene junction are calculated using many-body theory, and compared to the predictions of the figure-of-merit ZT.Comment: 5 pages, 6 figure

Direct observation of electron doping in La0.7Ce0.3MnO3 using x-ray absorption spectroscopy

We report on a X-ray absorption spectroscopic (XAS) study on a thin film of La0.7Ce0.3MnO3, a manganite which was previously only speculated to be an electron doped system. The measurements clearly show that the cerium is in the Ce(IV) valence state and that the manganese is present in a mixture of Mn2+ and Mn3+ valence states. These data unambiguously demonstrate that La0.7Ce0.3MnO3 is an electron doped colossal magnetoresistive manganite, a finding that may open up new opportunities both for device applications as well as for further basic research towards a better modelling of the colossal magnetoresistance phenomenon in these materials.Comment: 4 pages, 3 figures, revised versio

Resonant transmission through an open quantum dot

We have measured the low-temperature transport properties of a quantum dot formed in a one-dimensional channel. In zero magnetic field this device shows quantized ballistic conductance plateaus with resonant tunneling peaks in each transition region between plateaus. Studies of this structure as a function of applied perpendicular magnetic field and source-drain bias indicate that resonant structure deriving from tightly bound states is split by Coulomb charging at zero magnetic field.Comment: To be published in Phys. Rev. B (1997). 8 LaTex pages with 5 figure