Enhanced electron correlations, local moments, and Curie temperature in strained MnAs nanocrystals embedded in GaAs

We have studied the electronic structure of hexagonal MnAs, as epitaxial continuous film on GaAs(001) and as nanocrystals embedded in GaAs, by Mn 2p core-level photoemission spectroscopy. Configuration-interaction analyses based on a cluster model show that the ground state of the embedded MnAs nanocrystals is dominated by a d5 configuration that maximizes the local Mn moment. Nanoscaling and strain significantly alter the properties of MnAs. Internal strain in the nanocrystals results in reduced p-d hybridization and enhanced ionic character of the Mn-As bonding interactions. The spatial confinement and reduced p-d hybridization in the nanocrystals lead to enhanced d-electron localization, triggering d-d electron correlations and enhancing local Mn moments. These changes in the electronic structure of MnAs have an advantageous effect on the Curie temperature of the nanocrystals, which is measured to be remarkably higher than that of bulk MnAs.Comment: 4 figures, 2 table

Electronic states in arsenic-decapped MnAs (1100) films grown on GaAs(001): A photoemission spectroscopy study

3 pages, 2 figures.We examine the arsenic bonding in the near-surface region of initially arsenic-capped MnAs(1100) films grown on GaAs(001) as it evolves upon arsenic decapping. Line-shape analyses of high-resolution As 3d photoelectron emission spectra recorded at room temperature RT allow us to identify electronically distinct As-bonding states associated to bulk MnAs phases, bulk arsenic, and interfacial environments. Stable MnAs phases appear to be affected by the presence of a thin arsenic coating, an effect that could be advantageously used to enhance the ferromagnetic properties of MnAs films around RTWe thank the BESSY staff for support. This work has been supported by the Spanish Ministry of Education and Science (“Ramón y Cajal” and “Materials” Programs, 2005 call and MAT2004-05348 Grant, respectively) and by the German Federal Ministry for Education and Research.Peer reviewe

Si and Be intralayers at GaAs/AlAs and GaAs/GaAs junctions: Low-temperature photoemission measurements

In order to distinguish between conflicting interpretations regarding the effect of intralayer insertion at semiconductor junctions, we have carried out synchrotron-radiation photoemission studies of GaAs/AlAs(100) heterojunctions and GaAs/GaAs(110) homojunctions, with and without a Si or a Be intralayer, at room temperature and at low temperature. The synchrotron light induces photovoltage effects at low temperature, which are found to be consistent with the room-temperature band profiles we have previously proposed for these heterojunctions [M. Moreno et al., Phys. Rev. B 58, 13 767 (1998)], assuming a doping role for the intralayer atoms. Band discontinuities play an important role in determining the type of photovoltage effects induced. Our experimental observations can be fully understood in terms of intralayer-induced changes of the bandbending profile, and the occurrence of photovoltage effects at low temperature, calling into question the previous interpretation of room-temperature photoemission results from GaAs/AlAs heterojunctions in terms of intralayer-induced "band-offset" changes

Photoemission results on intralayer insertion at III-V/III-V junctions: A critical appraisal of the different interpretations

Several researchers have proposed that band discontinuities at semiconductor heterojunctions may be "tuned" by inserting very thin layers of foreign atoms at the interface which are thought to induce an "interface dipole." Modifications of the apparent valence-band offset, as measured by photoelectron spectroscopy (PES), have been indeed observed upon Si insertion at GaAs–AlAs interfaces, and they have been generally interpreted as real band-offset changes. However, there is an alternative explanation of the photoemission results in terms of band-bending effects. Here, we present results of PES experiments designed to test the two opposing interpretations. We have examined the effect of Si insertion at polar (100) and nonpolar (110) interfaces, and we have studied the insertion of Si (n-type) and Be (p-type) intralayers. Similar results are obtained for polar and nonpolar interfaces, and effects of opposite sign are observed for Si and Be intralayers. These results can be readily interpreted in terms of a band-bending profile modification upon Si or Be insertion. Additional PES experiments performed at different substrate temperatures have allowed us to test the proposed band profiles. From the surface photovoltage effects induced at low temperature, we obtain evidence for sample band bending which is consistent with the room-temperature band profiles proposed. Hence, our results can be completely understood within a "band-bending interpretation," calling into question the interpretation in terms of a "band-offset tuning effect.

Si intralayers at GaAs/AlAs and GaAs/GaAs junctions: Polar versus nonpolar interfaces

The effect of inserting thin Si intralayers at GaAs/AlAs and GaAs/GaAs interfaces has been studied by photoelectron spectroscopy (PES) using synchrotron radiation. Results from polar and nonpolar interfaces are compared by analyzing samples grown by molecular-beam epitaxy on (100) and (110) substrates, respectively. The Si intralayers were inserted by an improved δ-doping method in a concentration of 2.2×1014 cm−2 [about 1/3 of a (100) monolayer]. When Si is introduced at GaAs-on-AlAs interfaces, the Al(2p)-to-Ga(3d) energy distance is observed to increase for both polar and nonpolar interface orientations. The insertion of Si at GaAs/GaAs(110) homojunctions modifies the line shape of the Ga(3d) and As(3d) peaks, resembling the changes previously reported for the (100) orientation. The results on polar junctions previously obtained were generally interpreted as band-offset changes, which would be related according to the “interface microscopic capacitor” picture with the polar nature of the interface. The PES results here presented are difficult to reconcile with such a model because of the similar behavior shown by polar and nonpolar interfaces. Instead, they can be understood within an “overlayer band bending” interpretation

The 'not-so-strange' body in the mirror: : A principal components analysis of direct and mirror self-observation

This document is the Accepted Manuscript version of the following article: Paul M. Jenkinson, and Catherine Preston, ‘The “not-so-strange” body in the mirror: A principal components analysis of direct and mirror self-observation’, Consciousness and Cognition, Vol. 48, pp. 262-272, first published online 4 January 2017, doi: http://dx.doi.org/10.1016/j.concog.2016.12.007 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.In this study we adopted a psychometric approach to examine how the body is subjectively experienced in a mirror. One hundred and twenty-four healthy participants viewed their body for five minutes directly or via a mirror, and then completed a 20-item questionnaire designed to capture subjective experiences of the body. PCA revealed a two-component structure for both direct and mirror conditions, comprising body evaluations (and alienation) and unusual feelings and perceptions. The relationship between these components and pre-existing tendencies for appearance anxiety, body dysmorphic-type beliefs, dissociative symptomatology, self-objectification and delusion ideation further supported the similarity between direct and mirror conditions; however, the occurrence of strange experiences like those reported to occur during prolonged face viewing was not confirmed. These results suggest that, despite obvious differences in visual feedback, observing the body via a mirror (as an outside observer) is subjectively equivalent to observing the body directly (from our own viewpoint).Peer reviewedFinal Accepted Versio

Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio to Q^2 = 8.5 GeV^2

Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5 GeV2. By extending the range of Q2 for which GEp is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the non-perturbative regime

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13

Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector

A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13  TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139  fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV