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  • 1.
    Berggren, Karl-Fredrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Yakimenko, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Hakanen, Jani
    Ericsson AB.
    Modeling of open quantum dots and wave billiards using imaginary potentials for the source and the sink2010In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 12, no 073005Article in journal (Refereed)
    Abstract [en]

    A heuristic model for particle states and current flow in open ballistictwo-dimensional (2D) quantum dots/wave billiards is proposed. The modelmakes use of complex potentials first introduced in phenomenological nuclearinelastic scattering theory (the optical model). Here we assume that externalinput and output leads connecting the system to the source and the drain regionsmay be represented by complex potentials. In this way, a current may be set upbetween the two ‘pseudo-leads’. Probability densities and current flows for anopen quantum dot are analyzed here numerically and the results are comparedwith the microwave measurements used to emulate the system. The model isof conceptual as well as practical interest. In addition to quantum billiards, itmay be used as a tool per se to analyze transport in classical wave analogues,such as microwave resonators, acoustic resonators, effects of leakage on suchsystems, etc.

  • 2.
    Davidsson, Joel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ivády, Viktor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Acad Sci, Hungary.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nguyen, Son Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    First principles predictions of magneto-optical data for semiconductor point defect identification: the case of divacancy defects in 4H-SiC2018In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, article id 023035Article in journal (Refereed)
    Abstract [en]

    Study and design of magneto-optically active single point defects in semiconductors are rapidly growing fields due to their potential in quantum bit (qubit) and single photon emitter applications. Detailed understanding of the properties of candidate defects is essential for these applications, and requires the identification of the defects microscopic configuration and electronic structure. In multicomponent semiconductors point defects often exhibit several non-equivalent configurations of similar but different characteristics. The most relevant example of such point defect is the divacancy in silicon carbide, where some of the non-equivalent configurations implement room temperature qubits. Here, we identify four different configurations of the divacancy in 4H-SiC via the comparison of experimental measurements and results of first-principle calculations. In order to accomplish this challenging task, we carry out an exhaustive numerical accuracy investigation of zero-phonon line and hyperfine coupling parameter calculations. Based on these results, we discuss the possibility of systematic quantum bit search.

  • 3.
    Dieckmann, Mark E
    et al.
    Ruhr-University Bochum.
    Bret, Antoine
    ETSI Ind Univ Castilla-La Mancha.
    Shukla, Padma K
    Institute of Theoretical Physics IV uhr-University Bochum, Germany.
    Electron surfing acceleration by mildly relativistic beams: wave magnetic field effects2008In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 10, no Januar, p. 013029-1-13029-2Article in journal (Refereed)
    Abstract [en]

    Electron surfing acceleration (ESA) is based on the trapping of electrons by a wave and the transport of the trapped electrons across a perpendicular magnetic field. ESA can accelerate electrons to relativistic speeds and it may thus produce hot electrons in plasmas supporting fast ion beams, like close to astrophysical shocks. One-dimensional (1D) particle-in-cell (PIC) simulations have demonstrated that trapped electron structures (phase space holes) are stabilized by relativistic phase speeds of the waves, by which ESA can accelerate electrons to ultrarelativistic speeds. The 2(1/2)D electromagnetic and relativistic PIC simulations performed in the present paper model proton beam driven instabilities in the presence of a magnetic field perpendicular to the simulation plane. This configuration represents the partially electromagnetic mixed modes and the filamentation modes, in addition to the Buneman waves. The waves are found to become predominantly electromagnetic and nonplanar for beam speeds that would result in stable trapped electron structures. The relativistic boost of ESA reported previously is cancelled by this effect. For proton beam speeds of 0.6 and 0.8c, the electrons reach only million electron volt energies. The system with the slower beam is followed sufficiently long in time to reveal the development of a secondary filamentation instability. The instability forms a channel in the simulation domain that is void of any magnetic field. Proton beams may thereby cross perpendicular magnetic fields for distances beyond their gyroradius.

  • 4.
    Dieckmann, Mark E
    et al.
    Ruhr-University Bochum.
    Lerche, Ian
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Drury, Luke OC
    School of Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    Aspects of self-similar current distributions resulting from the plasma filamentation instability2007In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9, p. 10-1-10-22Article in journal (Refereed)
    Abstract [en]

    Colliding plasmas can form current filaments that are magnetically confined and interact through electromagnetic fields during the nonlinear evolution of this filamentation instability. A nonrelativistic and a relativistic electron flow are examined. Two-dimensional (2D) particle-in-cell (PIC) simulations evolve the instability in a plane orthogonal to the flow vector and confirm that the current filaments move, merge through magnetic reconnection and evolve into current sheets and large flux tubes. The current filaments overlap over limited spatial intervals. Electrons accelerate in the overlap region and their final energy distribution decreases faster than exponential. The spatial power spectrum of the filaments in the flow-aligned current component can be approximated by a power-law during the linear growth phase. This may reflect a phase transition. The power spectrum of the current component perpendicular to the flow direction shows a power-law also during the nonlinear phase, possibly due to preferential attachment. The power-law distributed power spectra evidence self-similarity over a limited scale size and the wavenumber of the maximum of the spatial power spectrum of the filament distribution decreases linearly in time. Power-law correlations of velocity fields, which could be connected to the current filaments, may imply super-diffusion.

  • 5.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    OC Drury, Luke
    School of Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    On the ultrarelativistic two-stream instability, electrostatic turbulence and Brownian motion2006In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 8Article in journal (Refereed)
    Abstract [en]

    Experimental evidence indicates that bulk plasma flow at ultrarelativistic speeds is common in astrophysical settings, e.g. the collimated jets of active galactic nuclei and gamma ray bursts. The low-plasma density of such flows implies their collisionless relaxation by means of wave-particle interactions. Such processes are not well understood in the ultrarelativistic regime. The thermalization of two interpenetrating equally dense electron-proton (e -p) beams in the absence of a magnetic field is examined here by means of 1.5D particle-in-cell simulations. The relative beam speeds correspond to Lorentz factors in the range 200-1000. The constraint to one spatial simulation dimension, which is aligned with the beam velocity vectors, implies that only the two-stream (TS) instability and the Weibel-type instability can grow, while filamentation instabilities are excluded. With this constraint and for our plasma parameters, the TS instability dominates. The electrostatic waves grow, saturate by the trapping of electrons, and collapse. The interaction of the electrons with the electric fields after the wave collapse represents a relativistic Wiener process. In response, the electrons are rapidly thermalized. The final electron distribution can be interpreted as a relativistic Maxwellian distribution with a high-energy tail arising from ultrarelativistic phase space holes. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

  • 6.
    Dieckmann, Mark E
    et al.
    Ruhr-University Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Eliasson, Bengt
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Particle-in-cell simulations of plasma slabs colliding at a mildly relativistic speed2006In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 8, no October, p. 225-1-225-21Article in journal (Refereed)
    Abstract [en]

    Plasmas collide at relativistic speeds in many astrophysical and high-energy density laboratory environments. The boundaries that develop between such plasmas and expand at much larger speeds than the ion sound speed cs are not well understood. Here, we address two identical electron-proton plasma slabs that collide with a relativistic speed and a Mach number v/cs of over 400. The collision speed, the plasma temperature and magnetic field are such that the growth rate of the two-stream instability exceeds that of all other instabilities. We model a planar turbulent boundary (TB) with one-dimensional (1D) and 2D particle-in-cell (PIC) simulations. We show that the boundary dissipates its energy via electron phase space holes (EPSHs) that accelerate electrons at the boundary to relativistic speeds and increase significantly the speed of some protons. Our results are put into the context of a dynamic accretion disc and the jet of a microquasar. It is shown that the accelerated electrons could contribute to the disc wind and to relativistic leptonic jets, and possibly to the hard radiation component of the accretion disc.

  • 7.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Sarri, Gianluca
    Queen's University Belfast, UK.
    Doria, Domenico
    Queen's University Belfast, UK.
    Ahmed, Hamad
    Queen's University Belfast, UK.
    Borghesi, Marco
    Queen's University Belfast, UK.
    Evolution of slow electrostatic shock into a plasma shock mediated by electrostatic turbulence2014In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 16, p. 073001-1-073001-25Article in journal (Refereed)
    Abstract [en]

    The collision of two plasma clouds at a speed that exceeds the ion acoustic speed can result in the formation of shocks. This phenomenon is observed not only in astrophysical scenarios, such as the propagation of supernova remnant (SNR) blast shells into the interstellar medium, but also in laboratory-based laser-plasma experiments. These experiments and supporting simulations are thus seen as an attractive platform for small-scale reproduction and study of astrophysical shocks in the laboratory. We model two plasma clouds, which consist of electrons and ions, with a 2D particle-in-cell simulation. The ion temperatures of both clouds differ by a factor of ten. Both clouds collide at a speed that is realistic for laboratory studies and for SNR shocks in their late evolution phase, like that of RCW86. A magnetic field, which is orthogonal to the simulation plane, has a strength that is comparable to that of SNR shocks. A forward shock forms between the overlap layer of both plasma clouds and the cloud with cooler ions. A large-amplitude ion acoustic wave is observed between the overlap layer and the cloud with hotter ions. It does not steepen into a reverse shock because its speed is below the ion acoustic speed. A gradient of the magnetic field amplitude builds up close to the forward shock as it compresses the magnetic field. This gradient gives rise to an electron drift that is fast enough to trigger an instability. Electrostatic ion acoustic wave turbulence develops ahead of the shock, widens its transition layer, and thermalizes the ions, but the forward shock remains intact.

  • 8.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Sarri, Gianluca
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Murphy, Gareth
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Bret, Antoine
    Harvard-Smithsonian Center for Astrophysics.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France .
    Kourakis, Ioannis
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Borghesi, Marco
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Drury, Luke o'c
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    PIC simulation of a thermal anisotropy-driven Weibel instability in a circular rarefaction wave2012In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, no 023007Article in journal (Refereed)
    Abstract [en]

    The expansion of an initially unmagnetized planar rarefaction wave has recently been shown to trigger a thermal anisotropy-driven Weibel instability (TAWI), which can generate magnetic fields from noise levels. It is examined here whether the TAWI can also grow in a curved rarefaction wave. The expansion of an initially unmagnetized circular plasma cloud, which consists of protons and hot electrons, into a vacuum is modelled for this purpose with a two-dimensional particle-in-cell (PIC) simulation. It is shown that the momentum transfer from the electrons to the radially accelerating protons can indeed trigger a TAWI. Radial current channels form and the aperiodic growth of a magnetowave is observed, which has a magnetic field that is oriented orthogonal to the simulation plane. The induced electric field implies that the electron density gradient is no longer parallel to the electric field. Evidence is presented here that this electric field modification triggers a second magnetic instability, which results in a rotational low-frequency magnetowave. The relevance of the TAWI is discussed for the growth of small-scale magnetic fields in astrophysical environments, which are needed to explain the electromagnetic emissions by astrophysical jets. It is outlined how this instability could be examined experimentally.

  • 9.
    Eliasson, B.
    et al.
    Fakultät f Physik und Astronomie, Institut f Theoretische Physik IV Ruhr-Universität Bochum.
    Dieckmann, Mark E
    Ruhr-Universität Bochum.
    Shukla, P. K.
    Fakultät f Physik und Astronomie, Institut f Theoretische Physik IV Ruhr-Universität Bochum.
    Simulation study of surfing acceleration in magnetized space plasmas2005In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 7Article in journal (Refereed)
    Abstract [en]

    We present a numerical study of the surfing mechanism in which electrons are trapped in Bernstein-Greene-Kruskal (BGK) modes, and are accelerated across the magnetic field direction by the Lorentz force in magnetized space plasmas. The BGK modes are the product of an ion-beam Buneman instability that excites large-amplitude electrostatic upper-hybrid waves in the plasma. Our study, which is performed with particle-in-cell (PIC) and Vlasov codes, reveals the stability of the BGK mode as a function of the magnetic field strength and the ion beam speed. It is found that the surfing acceleration is more effective for a weaker magnetic field owing to the longer lifetime of the BGK modes. The importance of our investigation to electron acceleration in astrophysical environments has been emphasized. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

  • 10.
    Eliasson, Bengt
    et al.
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Dieckmann, Mark E
    Ruhr-Universität Bochum.
    Theoretical and simulation studies of relativistic ion holes in astrophysical plasmas2006In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 8, no April, p. 55-1-55-12Article in journal (Refereed)
    Abstract [en]

    Theoretical and numerical studies of relativistic ion holes in a relativistically hot electron-ion plasma are presented. Previous particle-in-cell (PIC) simulations have shown that the ion holes are formed as a result of relativistic beam-plasma instabilities in the foreshock region of internal shocks of gamma-ray bursts and the relativistic jets of active galactic nuclei. In this process, the electrons are heated to ultra-relativistic temperatures so that their relativistic mass becomes comparable to the proton mass, and relativistic ion holes are formed by a secondary ion beam instability. The electrostatic potentials associated with the ion holes are large enough to accelerate particles to GeV energies. We use a semi-analytical model to construct relativistic ion holes and investigate their stability by means of fully relativistic Vlasov simulations. This investigation is relevant for astrophysical settings where the ion holes may work as efficient particle accelerators.

  • 11.
    Feng, Qingguo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Topological transitions of the Fermi surface of osmium under pressure: an LDA plus DMFT study2017In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 19, article id 033020Article in journal (Refereed)
    Abstract [en]

    The influence of pressure on the electronic structure of Os has attracted substantial attention recently due to reports on isostructural electronic transitions in this metal. Here, we theoretically investigate the Fermi surface of Os from ambient to high pressure, using density functional theory combined with dynamical mean field theory. Weprovide a detailed discussion of the calculated Fermi surface and its dependence on the level of theory used for the treatment of the electron-electron interactions. Although we confirm that Os can be classified as weakly correlated metal, the inclusion of local quantum fluctuations between 5d electrons beyond the local density approximation explains the most recent experimental reports regarding the occurrence of electronic topological transitions in Os.

  • 12.
    Janssen, T J B M
    et al.
    National Phys Lab, England .
    Fletcher, N E
    Bur Int Poids and Mesures.
    Goebel, R
    Bur Int Poids and Mesures.
    Williams, J M
    National Phys Lab, England .
    Tzalenchuk, A
    National Phys Lab, England .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kubatkin, S
    Chalmers.
    Lara-Avila, S
    Chalmers.
    Falko, V I
    University of Lancaster.
    Graphene, universality of the quantum Hall effect and redefinition of the SI system2011In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, no 9, p. 093026-Article in journal (Refereed)
    Abstract [en]

    The Systeme Internationale dunites (SI) is about to undergo its biggest change in half a century by redefining the units for mass and current in terms of the fundamental constants h and e, respectively. This change crucially relies on the exactness of the relationships that link these constants to measurable quantities. Here we report the first direct comparison of the integer quantum Hall effect (QHE) in epitaxial graphene with that in GaAs/AlGaAs heterostructures. We find no difference in the quantized resistance value within the relative standard uncertainty of our measurement of 8.6 x 10(-11), this being the most stringent test of the universality of the QHE in terms of material independence.

  • 13.
    Karlsson, K Fredrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Oberli, D Y
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Dupertuis, M A
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Troncale, V
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Byszewski, M
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Pelucchi, E
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Rudra, A
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kapon, E
    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Physics of Nanostructures, CH-1015 Lausanne, Switzerland.
    Spectral signatures of high-symmetry quantum dots and effects of symmetry breaking2015In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, no 10Article in journal (Refereed)
    Abstract [en]

    High symmetry epitaxial quantum dots (QDs) with three or more symmetry planes provide a very promising route for the generation of entangled photons for quantum information applications. The great challenge to fabricate nanoscopic high symmetry QDs is further complicated by the lack of structural characterization techniques able to resolve small symmetry breaking. In this work, we present an approach for identifying and analyzing the signatures of symmetry breaking in the optical spectra of QDs. Exciton complexes in InGaAs/AlGaAs QDs grown along the [111]B crystalline axis in inverted tetrahedral pyramids are studied by polarization resolved photoluminescence spectroscopy combined with lattice temperature dependence, excitation power dependence and temporal photon correlation measurements. By combining such a systematic experimental approach with a simple theoretical approach based on a point-group symmetry analysis of the polarized emission patterns of each exciton complex, we demonstrate that it is possible to achieve a strict and coherent identification of all the observable spectral patterns of numerous exciton complexes and a quantitative determination of the fine structure splittings of their quantum states. This analysis is found to be particularly powerful for selecting QDs with the highest degree of symmetry ( C 3 v and ##IMG## [http://ej.iop.org/images/1367-2630/17/10/103017/njp519062ieqn1.gif] $D_3h$ ) for potential applications of these QDs as polarization entangled photon sources. We exhibit the optical spectra when evolving towards asymmetrical QDs, and show the higher sensitivity of certain exciton complexes to symmetry breaking.

  • 14.
    Kleinmann, Matthias
    et al.
    University of Siegen.
    Guehne, Otfried
    University of Siegen.
    Portillo, Jose R.
    University of Seville.
    Larsson, Jan-Åke
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Cabello, Adan
    University of Seville.
    Memory cost of quantum contextuality2011In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, no 113011Article in journal (Refereed)
    Abstract [en]

    The simulation of quantum effects requires certain classical resources, and quantifying them is an important step to characterize the difference between quantum and classical physics. For a simulation of the phenomenon of state-independent quantum contextuality, we show that the minimum amount of memory used by the simulation is the critical resource. We derive optimal simulation strategies for important cases and prove that reproducing the results of sequential measurements on a two-qubit system requires more memory than the information-carrying capacity of the system.

  • 15.
    Lind, Hans
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Systematic theoretical search for alloys with increased thermal stability for advanced hard coatings applications2013In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 15Article in journal (Refereed)
    Abstract [en]

    State-of-the-art alloys for hard coating applications, such as TiAlN, are known to suffer from decreased hardness during heat treatment in excess of 900 °C due to the formation of detrimental wurtzite AlN phases. Recent research has shown that multicomponent alloying with additional transition metals (TMs) such as Cr can shift the onset of the phase transformations to higher temperatures, but a search for new alloys is generally time-consuming due to the large number of processes that influence material properties along with the large number of alloy compositions that have to be synthesized. To overcome this difficulty we carry out systematic first-principles calculations aimed at finding potential new multicomponent TM aluminum nitride alloys for advanced hard coating applications. We direct our search towards a specific property, the thermal stability of the coating. In particular, we concentrate on the thermodynamic stability of the cubic B1 TM–Al–N phase relative to the wurtzite phase, and choose the enthalpy difference between them as our search descriptor. We perform ab initio calculations for all TMs, considered as impurities in AlN, and identify the most promising candidates that may improve the thermal stability. We present arguments that these elements should be targeted in future in-depth studies, theoretical, as well as experimental.

  • 16.
    Osikowicz, Wojciech
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Sorensen, S.L.
    Lunds universitet.
    Groenendaal, L.
    AGFA-Gevaert.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Site-specific electronic structure of an oligo-ethylenedioxythiophene derivative probed by resonant photoemission2005In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 7Article in journal (Refereed)
    Abstract [en]

    A combination of conventional and resonant photoemission spectroscopy, x-ray absorption spectroscopy and ground-state quantum-chemical calculations has been used to study the valence electronic structure of a phenyl-capped 3,4-ethylenedioxythiophene oligomer, in polycrystalline thin films. The photon energy-dependent intensities of specific resonant decay channels are interpreted in terms of the spatial overlap of the excitation site and the ground-state molecular orbital involved in the decay. By making use of chemical shifts, excitations on different atomic sites are distinguished. It is demonstrated that site-specific information on the electronic structure of relatively large and complex organic systems may be obtained experimentally from non-radiative resonant decay spectra. In addition, these spectra provide relevant insight into the interpretation of near-edge x-ray absorption fine structure spectra. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

  • 17.
    Pourovskii, L. V.
    et al.
    Univ Paris Saclay, France; Coll France, France; Natl Univ Sci and Technol MISIS, Russia.
    Mravlje, J.
    Jozef Stefan Inst, Slovenia.
    Georges, A.
    Univ Paris Saclay, France; Coll France, France; Univ Geneva, Switzerland.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Correction: Electron-electron scattering and thermal conductivity of epsilon-iron at Earths core conditions (vol 19, 073022, 2017)2018In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, article id 109501Article in journal (Refereed)
    Abstract [en]

    n/a

  • 18.
    Pourovskii, L. V.
    et al.
    University of Paris Saclay, France; Coll France, France; National University of Science and Technology MISIS, Russia.
    Mravlje, J.
    Jozef Stefan Institute, Slovenia.
    Georges, A.
    University of Paris Saclay, France; Coll France, France; University of Geneva, Switzerland.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Electron-electron scattering and thermal conductivity of epsilon-iron at Earths core conditions2017In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 19, article id 073022Article in journal (Refereed)
    Abstract [en]

    The electronic state and transport properties of hot dense iron are of the utmost importance for the understanding of Earths interior. Combining state-of-the-art density functional and dynamical mean field theories we study the impact of electron correlations on the electrical and thermal resistivity of hexagonal close-packed epsilon-Fe at Earths core conditions and show that the electron-electron scattering in epsilon-Fe exhibit a nearly perfect Fermi-liquid (FL) behavior. Accordingly, the quadratic dependence of the scattering rate, typical of FLs, leads to a modification of the Wiedemann-Franz law and suppresses the thermal conductivity with respect to the electrical one. The consequence is a significant increase of the electron-electron thermal resistivity, which is found to be of comparable magnitude to the electron-phonon one.

  • 19.
    Rauter, P.
    et al.
    University of Linz.
    Fromherz, T.
    University of Linz.
    Vinh, N.Q.
    FOM Institute for Plasma Physics.
    Murdin, B.N.
    University of Surrey .
    Phillips, J.P.
    Heriot-Watt University.
    Pidgeon, C.R.
    Heriot-Watt University.
    Diehl, L.
    Paul Scherrer Institut.
    Dehlinger, G.
    Paul Scherrer Institut.
    Gruetzmacher, D.
    Paul Scherrer Institut.
    Zhao, Ming
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Ni, Wei-Xin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics . Linköping University, The Institute of Technology.
    Bauer, G.
    University of Linz.
    Direct determination of ultrafast intersubband hole relaxation times in voltage biased SiGe quantum wells by a density matrix interpretation of femtosecond resolved photocurrent experiments2007In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9Article in journal (Refereed)
    Abstract [en]

    We report the quantitative and direct determination of hole intersubband relaxation times in a voltage biased SiGe heterostructure using density matrix calculations applied to a four-level system in order to interpret photocurrent (PC) pump-pump experiments. One consistent set of parameters allows the simulation of two kinds of experiments, namely pump-pump photocurrent experiments at a free electron laser (wavelength 7.9 mu m) and the laser-power dependence of the PC signal. This strongly confirms the high reliability of these parameter values, of which the most interesting in respect to Si based quantum cascade laser development is the extracted heavy-hole relaxation time. The simulations show that this relaxation time directly determines the experimentally observed decay of the pump-pump photocurrent signal as a function of the delay time. For a heavy hole intersubband spacing of 160 meV, a value of 550 fs was obtained. The experimental method was further applied to determine the LH1-HH1 relaxation time of a second sample with a transition energy below the optical phonon energy. The observed relaxation time of 16 ps is consistent with the value found for the same structure by transmission pump-probe experiments.

  • 20.
    Rowlands, George
    et al.
    Physics Department Warwick University.
    Dieckmann, Mark E
    Ruhr-University Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum.
    The plasma filamentation instability in one dimension: nonlinear evolution2007In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9, no August, p. 247-1-247-15Article in journal (Refereed)
    Abstract [en]

    The plasma filamentation instability or beam-Weibel instability generates magnetic fields and accelerates particles in collisionless astrophysical plasma. This instability has been examined with multi-dimensional particle-in-cell (PIC) simulations, demonstrating the formation of current flux tubes. Such simulations could not model a statistically significant number of filaments. Here, we model with a PIC simulation the filamentation instability that is driven by nonrelativistic, cool electron beams in one spatial dimension at an unprecedented resolution. We show unambiguously that the gradient of the magnetic pressure which develops during the quasi-linear evolution of the filamentation instability, gives rise to an electrostatic field component. The interplay of the magnetic and electrostatic fields results in a wavenumber spectrum of the magnetic field that is a power-law, which has been reported previously for multi-dimensional PIC simulations. The magnetic field power spectrum decreases with the exponent -5.7 and that of the electrostatic field with -3.8, yielding a ratio of 3:2. The electromagnetic fields thermalize the electrons. The electrons develop a velocity distribution in the simulation direction that decreases exponentially at low speeds and faster at high speeds. The filamentation instability can thus not efficiently accelerate electrons to high energies. The filaments develop into a stationary final state. The probability distribution of the filament sizes is a Gumbel distribution. In astrophysical settings, this implies that the long exponential tail of this distribution may lead with a reasonable probability to large current filaments, if the filamentation instability develops in a large enough volume. The coherent magnetic fields of large filaments are required to explain the synchrotron emissions of gamma ray bursts.

  • 21.
    Sarri, G
    et al.
    Queen's University of Belfast.
    Cecchetti, C A
    Queen's University of Belfast.
    Romagnani, L
    Queen's University of Belfast.
    Brown, C M
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire .
    Hoarty, D J
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire.
    James, S
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire.
    Morton, J
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Jung, R
    Heinrich-Heine-Universitaat, Dusseldorf.
    Willi, O
    Heinrich-Heine-Universitaat, Dusseldorf.
    Bulanov, S V
    APRC, JAEA, Kizugawa, Kyoto.
    Pegoraro, F
    Universit di Pisa.
    Borghesi, Marco
    Queen's University of Belfast.
    The application of laser-driven proton beams to the radiography of intense laser–hohlraum interactions2010In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 12, no 4, p. 045006-Article in journal (Refereed)
    Abstract [en]

    Plasma expansion following the interaction of an intense laser beam with the inner surface of gold hohlraums, emulating conditions relevant to indirect drive inertial confinement fusion (ICF), has been investigated by a radiographic technique which employs a beam of laser-accelerated protons. This probing technique has made it possible to measure the electric field distribution associated with the plasma front and its propagation throughout the interior of the hohlraum with a temporal and spatial resolution of the order of a few ps and μm, respectively. The data indicate that the expanding plasma slows down approaching the opposite walls, possibly due to the interaction with x-ray heated plasma from the non-irradiated walls. The electric field at the plasma front shows a bipolar structure, suggesting the presence of ion-acoustic soliton-like structures cotraveling with the front. Data obtained using enclosed hohlraums suggest the feasibility of this type of diagnosis in gas-filled hohlraums, as currently employed in ICF experiments.

  • 22.
    Sarri, Gianluca
    et al.
    Queen's University of Belfast, UK.
    Murphy, Gareth Charles
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Bret, Antoine
    ETSI Ind, University of Castilla-LaMancha, Spain.
    Quinn, Kevin
    Queen's University of Belfast, UK.
    Kourakis, Ioannis
    Queen's University of Belfast, UK.
    Borghesi, Marco
    Queen's University of Belfast, UK.
    Drury, Luke o'C
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Two-dimensional particle-in-cell simulation of the expansion of a plasma into a rarefied medium2011In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, no 7, p. 073023-1-073023-23Article in journal (Refereed)
    Abstract [en]

    The expansion of a dense plasma through a more rarefied ionized medium has been studied by means of two-dimensional particle-in-cell simulations. The initial conditions involve a density jump by a factor of 100, located in the middle of an otherwise equally dense electron-proton plasma with uniform proton and electron temperatures of 10 eV and 1keV, respectively. Simulations show the creation of a purely electrostatic collisionless shock together with an ion-acoustic soliton tied to its downstream region. The shock front is seen to evolve in filamentary structures consistently with the onset of the ion-ion instability. Meanwhile, an un-magnetized drift instability is triggered in the core part of the dense plasma. Such results explain recent laser-plasma experiments, carried out in similar conditions, and are of intrinsic relevance to non-relativistic shock scenarios in the solar and astrophysical systems.

  • 23.
    Willander, Magnus
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Bano, N.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sultana, K.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zinc oxide nanorod-based heterostructures on solid and soft substrates for white-light-emitting diode applications2009In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 11, no 125020Article in journal (Refereed)
    Abstract [en]

    ZnO nanorods with excellent optical and electro-optical emission characteristics were grown using high-and low-temperature techniques on solid and soft substrate materials. The solid crystalline substrates included p-4H-SiC and p-GaN, while the soft amorphous substrates included p-type polymers deposited on glass and flexible plastic. Two different growth approaches were used to produce these samples. We used the vapor-liquid-solid (VLS) technique (high temperature) and aqueous chemical growth (ACG), which is a low-temperature technique. These ZnO nanorod samples were characterized by room temperature photoluminescence (PL) and processed to fabricate light-emitting diodes (LEDs). The LED characteristics were further investigated by I-V and electroluminescence (EL). As observed by PL measurements, all samples revealed a sharp narrow ultraviolet (UV) peak due to band-edge emission, indicating the good crystalline quality of the grown ZnO nanorods. The origin of the different peaks within the visible region was correlated to different deep level defects reported earlier for ZnO. All fabricated LEDs showed EL providing a wide band extended through the whole visible spectrum and hence produced clear white light observable to the naked eye. The emitted color quality investigation showed that superior color quality was manifested in a high color rendering index and stable color under current variation, indicating that these heterojunction and hybrid LEDs have potential for the development of future light sources. The ZnO nanorod-based LEDs grown by low-temperature ACG on glass and flexible plastic can, after further development, be candidates for future large-area white-light sources.

1 - 23 of 23
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