Nanosized superparamagnetic precipitates in cobalt-doped ZnO

The existence of semiconductors exhibiting long-range ferromagnetic ordering at room temperature still is controversial. One particularly important issue is the presence of secondary magnetic phases such as clusters, segregations, etc... These are often tedious to detect, leading to contradictory interpretations. We show that in our cobalt doped ZnO films grown homoepitaxially on single crystalline ZnO substrates the magnetism unambiguously stems from metallic cobalt nano-inclusions. The magnetic behavior was investigated by SQUID magnetometry, x-ray magnetic circular dichroism, and AC susceptibility measurements. The results were correlated to a detailed microstructural analysis based on high resolution x-ray diffraction, transmission electron microscopy, and electron-spectroscopic imaging. No evidence for carrier mediated ferromagnetic exchange between diluted cobalt moments was found. In contrast, the combined data provide clear evidence that the observed room temperature ferromagnetic-like behavior originates from nanometer sized superparamagnetic metallic cobalt precipitates.Comment: 20 pages, 6 figures; details about background subtraction added to section III. (XMCD

How to Create an Innovation Accelerator

Too many policy failures are fundamentally failures of knowledge. This has become particularly apparent during the recent financial and economic crisis, which is questioning the validity of mainstream scholarly paradigms. We propose to pursue a multi-disciplinary approach and to establish new institutional settings which remove or reduce obstacles impeding efficient knowledge creation. We provided suggestions on (i) how to modernize and improve the academic publication system, and (ii) how to support scientific coordination, communication, and co-creation in large-scale multi-disciplinary projects. Both constitute important elements of what we envision to be a novel ICT infrastructure called "Innovation Accelerator" or "Knowledge Accelerator".Comment: 32 pages, Visioneer White Paper, see http://www.visioneer.ethz.c

Entanglement capability of self-inverse Hamiltonian evolution

We determine the entanglement capability of self-inverse Hamiltonian evolution, which reduces to the known result for Ising Hamiltonian, and identify optimal input states for yielding the maximal entanglement rate. We introduce the concept of the operator entanglement rate, and find that the maximal operator entanglement rate gives a lower bound on the entanglement capability of a general Hamiltonian.Comment: 4 pages, no figures. Version 3: small change

Fermionic massive modes along cosmic strings

The influence on cosmic string dynamics of fermionic massive bound states propagating in the vortex, and getting their mass only from coupling to the string forming Higgs field, is studied. Such massive fermionic currents are numerically found to exist for a wide range of model parameters and seen to modify drastically the usual string dynamics coming from the zero mode currents alone. In particular, by means of a quantization procedure, a new equation of state describing cosmic strings with any kind of fermionic current, massive or massless, is derived and found to involve, at least, one state parameter per trapped fermion species. This equation of state exhibits transitions from subsonic to supersonic regimes while the massive modes are filled.Comment: 27 pages, 15 figures, uses ReVTeX. Shortened version, accepted for publication in Phys. Rev.

Equation of state of cosmic strings with fermionic current-carriers

The relevant characteristic features, including energy per unit length and tension, of a cosmic string carrying massless fermionic currents in the framework of the Witten model in the neutral limit are derived through quantization of the spinor fields along the string. The construction of a Fock space is performed by means of a separation between longitudinal modes and the so-called transverse zero energy solutions of the Dirac equation in the vortex. As a result, quantization leads to a set of naturally defined state parameters which are the number densities of particles and anti-particles trapped in the cosmic string. It is seen that the usual one-parameter formalism for describing the macroscopic dynamics of current-carrying vortices is not sufficient in the case of fermionic carriers.Comment: 30 pages, 15 figures, uses ReVTeX, equation of state corrected, comments and references added. Accepted for publication in Phys. Rev.

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio