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  • 1.
    Andersson, Mikael Svante
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    De Toro, Jose Angel
    Lee, Su Seong
    Mathieu, Roland
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Ageing dynamics of a superspin glass2014Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 108, nr 1, s. 17004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetization dynamics of a model superspin glass system consisting of nearly monodispersed close-packed maghemite particles of diameter 8 nm is investigated. The observed non-equilibrium features of the dynamics are qualitatively similar to those of atomic spin glass systems. The intrinsic relaxation function, as observed in zero-field-cooled magnetization relaxation experiments, depends on the time the sample has been kept at constant temperature (ageing). Accompanying low-field experiments show that the archetypal spin glass characteristics -ageing, memory and rejuvenation- are reproduced in this dense system of dipolar-dipolar interacting superspins.  

  • 2.
    Azimi Mousolou, Vahid
    et al.
    School of Computer Science, Physics and Mathematics, Linnaeus Univ., Sweden.
    Canali, Carlo M.
    School of Computer Science, Physics and Mathematics, Linnaeus Univ., Sweden.
    Sjöqvist, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Teoretisk kemi.
    Non-Abelian off-diagonal geometric phases in nano-engineered four-qubit systems2013Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 103, nr 6, s. 60011-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The concept of off-diagonal geometric phase (GP) has been introduced in order to recover interference information about the geometry of quantal evolution where the standard GPs are not well-defined. In this Letter, we propose a physical setting for realizing non-Abelian off- diagonal GPs. The proposed non-Abelian off-diagonal GPs can be implemented in a cyclic chain of four qubits with controllable nearest-neighbor interactions. Our proposal seems to be within reach in various nano-engineered systems and therefore opens up for first experimental test of the non-Abelian off-diagonal GP. 

  • 3.
    Berggren, Peter
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Fransson, Jonas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Spin inelastic electron tunneling spectroscopy on local magnetic moment embedded in Josephson junction2014Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 108, nr 6, artikkel-id 67009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent experimental conductance measurements performed on paramagnetic molecular adsorbates on a superconducting surface, using superconducting scanning tunneling microscopy techniques, are theoretically investigated. For low temperatures, we demonstrate that tunneling current assisted excitations of the local magnetic moment cannot occur for voltage biases smaller than the superconducting gap of the scanning tunneling microscope. The magnetic moment is only excited for voltages corresponding to the sum of the superconducting gap and the spin excitation energies. In excellent agreement with experiment, we show that pumping into higher excitations gives additional current signatures by accumulation of density in the lower ones. Using external magnetic fields, we Zeeman-split the possible degeneracy and thereby resolve all excitations comprised in the magnetic moment.

  • 4.
    Bramwell, Steven T.
    et al.
    UCL, London Ctr Nanotechnol, 17-19 Gordon St, London WC1H 0AJ, England.;UCL, Dept Phys & Astron, London WC1H 0AJ, England..
    Faulkner, Michael F.
    UCL, London Ctr Nanotechnol, 17-19 Gordon St, London WC1H 0AJ, England.;UCL, Dept Phys & Astron, London WC1H 0AJ, England.;Univ Lyon, Lab Phys, Ecole Normale Super Lyon, F-69364 Lyon 07, France..
    Holdsworth, Peter C. W.
    Univ Lyon, Lab Phys, Ecole Normale Super Lyon, F-69364 Lyon 07, France..
    Taroni, Andrea
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Phase order in superfluid helium films2015Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 112, nr 5, artikkel-id 56003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Classic experimental data on helium films are transformed to estimate a finite-size phase order parameter that measures the thermal degradation of the condensate fraction in the two-dimensional superfluid. The order parameter is found to evolve thermally with the exponent beta = 3 pi(2)/128, a characteristic, in analogous magnetic systems, of the Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Universal scaling near the BKT fixed point generates a collapse of experimental data on helium and ferromagnetic films, and implies new experiments and theoretical protocols to explore the phase order. These results give a striking example of experimental finite-size scaling in a critical system that is broadly relevant to two-dimensional Bose fluids. This paper is dedicated to the memory of our friend and colleague Maxime Clusel, with whom we enjoyed many stimulating discussions on related topics.

  • 5.
    Caleman, Carl
    et al.
    Physik Department E17, Technische Universität München.
    Ortiz, Carlos
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Marklund, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Molekylär biofysik.
    Bultmark, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Gabrysch, Markus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Parak, F. G.
    Hajdu, Janos
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Molekylär biofysik.
    Klintenberg, Mattias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Timneanu, Nicusor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi, Molekylär biofysik.
    Radiation damage in biological material: electronic properties and electron impact ionization in urea2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 85, nr 1, s. 18005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radiation damage is an unavoidable process when performing structural investigations of biological macromolecules with X-rays. In crystallography this process can be limited through damage distribution in a crystal, while for single molecular imaging it can be outrun by employing short intense pulses. Secondary electron generation is crucial during damage formation and we present a study of urea, as model for biomaterial. From first principles we calculate the band structure and energy loss function, and subsequently the inelastic electron cross-section in urea. Using Molecular Dynamics simulations, we quantify the damage and study the magnitude and spatial extent of the electron cloud coming from an incident electron, as well as the dependence with initial energy.

  • 6.
    Carva, K
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Legut, D
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Oppeneer, Peter M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Influence of laser-excited electron distributions on the X-ray magnetic circular dichroism spectra: Implications for femtosecond demagnetization in Ni2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 86, nr 5, s. 57002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In pump-probe experiments an intensive laser pulse creates non-equilibrium excited-electron distributions in the first few hundred femtoseconds after the pulse. The influence of nonequilibrium electron distributions caused by a pump laser on the apparent X-ray magnetic circular dichroism (XMCD) signal of Ni is investigated theoretically here for the first time, considering electron distributions immediately after the pulse as well as thermalized ones, that are not in equilibrium with the lattice or spin systems. The XMCD signal is shown not to be simply proportional to the spin momentum in these situations. The computed spectra are compared to recent pump-probe XMCD experiments on Ni. We find that the majority of experimentally observed features considered to be a proof of ultrafast spin momentum transfer to the lattice can alternatively be attributed to non-equilibrium electron distributions. Furthermore, we find the XMCD sum rules for the atomic spin and orbital magnetic moment to remain valid, even for the laser-induced non-equilibrium electron distributions. Copyright (C) EPLA, 2009

  • 7.
    Cricchio, Francesco
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Grånäs, Oscar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Polarization of an open shell in the presence of spin-orbit coupling2011Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 94, nr 5, s. 57009-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There exist many f transition metal-based materials, with large orbital degeneracy and relatively strong spin-orbit coupling, that exhibits some multipolar order. We perform first-principles calculations on these systems within DFT method plus on-site Coulomb correction and we discuss the results in terms of polarization of the density occupation matrix. The fact that higher multipole polarizations play a larger role than the spin polarization indicates a breakdown of Hund's rules and we suggest a new complementary set of rules -Katt's rules, valid in case of large spin-orbit coupling interaction.

  • 8. Durakiewicz, T.
    et al.
    Riseborough, P. S.
    Olson, C. G.
    Joyce, J. J.
    Oppeneer, Peter M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Elgazzar, S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Bauer, E. D.
    Sarrao, J. L.
    Guziewicz, E.
    Moore, D. P.
    Butterfield, M. T.
    Graham, K. S.
    Observation of a kink in the dispersion of f-electrons2008Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 84, nr 3, s. 37003-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strong interactions in correlated electron systems may result in the formation of heavy quasiparticles that exhibit kinks in their dispersion relation. Spectral weight is incoherently shifted away from the Fermi energy, but Luttinger's theorem requires the Fermi volume to remain constant. Our angle-resolved photoemission study of USb2 reveals a kink in a noncrossing 5f band, representing the first experimental observation of a kink structure in f-electron systems. The kink energy scale of 21 meV and the ultra-small peak width of 3 meV are observed. We propose the novel mechanism of renormalization of a point-like Fermi surface, and that Luttinger's theorem remains applicable.

  • 9.
    Grönlund, Andreas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Matematiska institutionen.
    Eliasson, B.
    Marklund, M.
    Evolution of rogue waves in interacting wave systems2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 86, nr 2, s. 24001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Large-amplitude water waves on deep water have long been known in the seafaring community, and are the cause of great concern for, e.g., oil platform constructions. The concept of such freak waves is nowadays, thanks to satellite and radar measurements, well established within the scientific community. There are a number of important models and approaches for the theoretical description of such waves. By analyzing the scaling behavior of freak wave formation in a model of two interacting waves, described by two coupled non-linear Schrödinger equations, we show that there are two different dynamical scaling behaviors above and below a critical angle θc of the direction of the interacting waves, below which all wave systems evolve and display statistics similar to a wave system of non-interacting waves. The results equally apply to other systems described by the non-linear Schrödinger equations, and should be of interest when designing optical wave guides.

  • 10.
    Hjörvarsson, Björgvin
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Kudasov, Yuri
    Wolff, Max
    Hase, Thomas
    Chacon, Cyril
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    van Kampen, Maarten
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Liebig, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Zabel, Hartmut
    The influence of weak links on magnetic ordering in layered structures2008Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 61, nr 1, s. 17008-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We discuss the magnetic ordering in layered magnets with two different inherent ordering temperatures. A [V(12 ML)Fe(2 ML)/V(12 ML)(/Fe(3 ML)](70) superlattice with anti-ferromagnetic interlayer exchange coupling is used for this purpose. The more rapid decrease of the magnetic moment in the 2 monolayer thick Fe layers influences the ordering in a non-trivial way. A distribution of the effective ordering temperature is inferred, originating from a more rapid decrease of the magnetic moment in the near-surface region, as compared to the interior of the sample. The results clearly demonstrate the need to consider all energy and length scales when addressing ordering in materials with finite extension.

  • 11.
    Huang, L. M.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Århammar, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Araújo, C. Moysés
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Silvearv, Fredrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Tuning magnetic properties of In2O3 by control of intrinsic defects2010Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 89, nr 4, s. 47005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure and magnetic properties of In2O3 with four kinds of intrinsic point defects (O vacancy, In interstitial, O interstitial, and In vacancy) have been theoretically studied using the density functional theory. The defect energy states of the O vacancy and In interstitial are close to the bottom of conduction band and act as shallow donors, while the defect energy states of the In vacancy and O interstitial are just above the top of the valence band and act as shallow acceptors. Without addition of any magnetic ions, all the hole states are completely spin polarized, while the electron states display no spin polarization. This implies that semiconducting In2O3 can display magnetic ordering, purely due to the intrinsic defects. However, the formation energies for neutral p-type defects are too high to be thermodynamically stable at reasonable temperatures. Nevertheless, it is shown that negative charging can greatly decrease the formation energies of p-type defects, simultaneously removing the local magnetic moments. We conlcude that V-In''' and O-I '' will be the dominant compensating defects as In2O3 is doped with TM ions, such as Sn, Mo, V and Cr. This result is consistent with the general view that the p-type defect is a key feature to mediate ferromagnetic coupling between transition metal ions of dilute concentration in metal oxides. Copyright (C) EPLA, 2010

  • 12.
    Huang, Lunmei
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Araujo, C. Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Ahuja, R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Magnetic and electronic properties in 3d transition-metal-doped In2O3: An ab-initio study2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, nr 2, s. 27013-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The magnetic and electronic properties of the transition metal (TM) (V,   Cr, Mn, Fe, Co, Ni, Cu) doped In2O3 have been theoretically studied by   using the density functional theory. When two TM ions are placed close   to each other (TM-TM distance of about 3.4 angstrom), the ferromagnetic   ordering is found to be the lowest-energy configuration. The only   exception is Fe, which possesses a half-filled 3d band. However, for   further separation distance of about 7.2 angstrom, only Co, Ni and Cu   ions (having more than half-filled 3d band) still prefer the   ferromagnetic orientation, while V, Cr, or Mn ions (having less than   half-filled 3d band) prefer antiferromagnetic ordering. The energies of   the 3d band for TM ions show a decrease with increasing TM atomic   number. For V, Cr and Mn, the 3d bands are merged with the conduction   band, and show less hybridization with the host valence band; while for   Co, Ni and Cu, the 3d bands show strong hybridization with the host   valence band mainly formed by the oxygen 2p state. In this situation,   polarized holes are formed on the oxygen sites close to the TM ions.   Moreover, V-doped In2O3 is found to meet the requirements for a strong   donor-mediated ferromagnetism.

  • 13.
    Hussain, Tanveer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    De Sarkar, Abir
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Maark, Tuhina Adit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Sun, Weiwei
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Strain and doping effects on the energetics of hydrogen desorption from the MgH2 (001) surface2013Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 101, nr 2, s. 27006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On the basis of first-principles calculations we have systematically investigated the energetics of hydrogen desorption from the MgH2 (001) surface. Based on total energy and electronic structure calculations, two modes namely strain and doping of selected dopants (Al, Si, Ti) and the combined effect of both on the dehydrogenation energies (Delta H) of MgH2 (001) systems have been analyzed. The maximum improvement in Delta H has been obtained with the combined effect of doping and strain. Among all the dopants, Al gives the lowest value of Delta H when the system Al-MgH2 is subjected to a 7.5% biaxial symmetric strain whereas the Si-MgH2 systems show the least improvement in Delta H. The doping of Ti on MgH2 (001) is also very beneficial even without strain. The reduction in Delta H is caused by the charge localization on the metal atoms, destabilization and the weakening of metal-hydrogen bonds.

  • 14.
    Hussain, Tanveer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Pathak, Biswarup
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Maark, Tuhina Adit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Scheicher, Ralph H.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ab initio study of lithium-doped graphane for hydrogen storage2011Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 96, nr 2, s. 27013-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the first-principle density functional calculations we predict that Li-doped graphane (prehydrogenated graphene) can be a potential candidate for hydrogen storage. The calculated Li-binding energy on graphane is significantly higher than the Li bulk's cohesive energy ruling out any possibility of cluster formations in the Li-doped graphane. Our study shows that even with very low concentration (5.56%) of Li doping, the Li-graphane sheet can achieve a reasonable hydrogen storage capacity of 3.23 wt.%. The van der Waals corrected H(2) binding energies fall within the range of 0.12-0.29 eV, suitable for practical H(2) storage applications. 

  • 15.
    Hussain, Tanveer
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Pathak, Biswarup
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Maark, Tuhina Adit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Functionalization of graphane with alkali and alkaline-earth metals: An insulator-to-metallic transition2012Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, nr 4, s. 47004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In view of interest in functionalized carbon nanostructures due to their potential applications in nanotechnology and nanoelectronics, we have performed a systematic and thorough density functional theory (DFT) study on the interaction of the elements in the first two groups of the periodic table with graphane (hydrogenated graphene) sheet. GGA approximation as employed in DFT has been used to study in detail the binding configuration, bond length, charge transfer and band gap of each of these adatoms doped graphane (CH) systems. To have a better understanding of the adatoms-CH interaction, different doping concentrations varying from 3.125% to 50% have been considered. A certain trend in binding strength, bond length and charge transfer has been found in the case of both alkali metal and alkaline-earth metal adatoms. In the case of alkali-metal adatoms at the low doping concentration of 3.125%, semiconductor behavior was found, whereas at doping higher than this the compound showed metallic behavior. In contrast, alkaline-earth metal-doped CH exhibited metallic behavior at all the doping concentrations. Copyright (C) EPLA, 2012

  • 16. Jeong, H-K
    et al.
    Valla, T.
    Berger, Rolf
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi.
    Johnson, P. D.
    Smith, K. E.
    Experimental determination of the Fermi surface of the spin spiral compound TlCo2Se22007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 77, nr 2, s. 27001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure of TlCo2Se2 has been measured using high resolution angle resolved photoemission spectroscopy. TlCo2Se2 is thought to be an example of an incommensurate spin spiral system, where the magnetic moments of the cobalt layers are aligned ferromagnetically in the ab plane, but the magnetic moments are rotated by ~121° along the c-axis. However, experimental evidence in the electronic structure supporting spin spiral states has been lacking. Our experimental results clearly show the existence of band crossings near the Fermi level that are consistent with such states. Our data also reveal a remarkably heavily nested square Fermi surface in the plane perpendicular to the spin spiral, confirming the predicted quasi–two-dimensional electronic structure.

  • 17.
    Kaewmaraya, Thanayut
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Pathak, Biswarup
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Araujo, Carlos M
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Rosa, A. L.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Water adsorption on ZnO(10(1)over-bar0): The role of intrinsic defects2012Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, nr 1, s. 17014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective ZnO(10 (1) over bar0) surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.

  • 18. Kish, L. B.
    et al.
    Granqvist, Claes-Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Energy requirement of control: Comments on Szilard's engine and Maxwell's demon2012Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 98, nr 6, artikkel-id 68001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In mathematical physical analyses of Szilard's engine and Maxwell's demon, a general assumption (explicit or implicit) is that one can neglect the energy needed for relocating the piston in Szilard's engine and for driving the trap door in Maxwell's demon. If this basic assumption is wrong, then the conclusions of a vast literature on the implications of the second law of thermodynamics and of Landauer's erasure theorem are incorrect, too. Our analyses of the fundamental information physical aspects of various types of control within Szilard's engine and Maxwell's demon indicate that the entropy production due to the necessary generation of information yield much greater energy dissipation than the energy Szilard's engine is able to produce even if all sources of dissipation in the rest of these demons (due to measurement, decision, memory, etc.) are neglected.

  • 19.
    Kult, David
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kvantkemi.
    Åberg, Johan
    Centre for Quantum Computation, DAMTP, Univ. of Cambridge, UK.
    Sjöqvist, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kvantkemi.
    Non-Abelian generalization of off-diagonal geometric phases2007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 78, nr 6, s. 60004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    If a quantum system evolves in a noncyclic fashion the corresponding geometric phase or holonomy may not be fully defined. Off-diagonal geometric phases have been developed to deal with such cases. Here, we generalize these phases to the non-Abelian case, by introducing off-diagonal holonomies that involve evolution of more than one subspace of the underlying Hilbert space. Physical realizations of the off-diagonal holonomies in adiabatic evolution and interferometry are put forward.

  • 20. Learmonth, T.
    et al.
    McGuinness, C.
    Glans, P. -A
    Downes, J. E.
    Schmitt, Thorsten
    Swiss Light Source, Paul Scherrer Institute.
    Duda, Laurent-Claudius
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Guo, J. -H
    Chou, F. C.
    Smith, K. E.
    Observation of multiple Zhang-Rice excitations in a correlated solid: Resonant inelastic X-ray scattering study of Li2CuO22007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 79, nr 4, s. 47012-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multiple Zhang-Rice type spectral features have been observed in resonant inelastic X-ray scattering (RIXS) from the quasi -one-dimensional cuprate charge transfer insulator Li2CuO2. The first feature appears at constant emission energy, and is associated with a Zhang-Rice singlet final state. The second is an interplaquette charge transfer excitation that results in a novel triplet Zhang-Rice -type final state. It is accompanied by the presence of a O 2p nonbonding to upper Hubbard band excitation at an energy close to that of a calculated triplet charge transfer Zhang-Rice -type excitation. The site selectivity and polarization rules associated with RIXS allows these two excitations to be distinguished.

  • 21.
    Li, Yunguo
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Pathak, Biswarup
    Nisar, Jawad
    Qian, Zhao
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Metal-decorated graphene oxide for ammonia adsorption2013Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 103, nr 2, s. 28007-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the first-principles density functional theory, we have studied the stability, electronic structure and ammonia storage capacity of metal-decorated graphene oxide (GO). Metal atoms (Mg and Li) are bonded strongly to the epoxy oxygen atoms on the surface of the GO sheet, which can act as high-surface-area adsorbent for the ammonia uptake and release. Each metal atom can bind several ammonia molecules around itself with a reasonable binding energy. We find metal-decorated GO can store up to tens of moles of ammonia per kilogram, which is far better than the recently reported excellent ammonia adsorption by GO.

  • 22. Lizarraga, Raquel
    et al.
    Ramzan, Muhammad
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Araujo, Carlos Moyses
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Blomqvist, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Holmström, Erik
    Structural characterization of amorphous YCrO3 from first principles2012Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, nr 5, s. 57010-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We perform a theoretical prediction of the structure of amorphous YCrO3. We obtained equivalent amorphous structures by means of two independent first principles density functional theory based methods: molecular dynamics and stochastic quenching. In our structural analysis we include radial and angle distribution functions as well as calculations of bond lengths and average coordination numbers. We find Cr+3 atoms situated in slightly distorted oxygen octahedra throughout the amorphous structures and that the distribution of these octahedra is disordered. The presence of the same Cr+3 local environments that give rise to ferroelectricity in the orthorhombic perovskite structure suggests that the amorphous phase of YCrO3 may also exhibit ferroelectric properties. Copyright (c) EPLA, 2012

  • 23.
    LUNDGREN, L
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    NORDBLAD, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    SANDLUND, L
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    MEMORY BEHAVIOR OF THE SPIN-GLASS RELAXATION1986Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 1, s. 529-534Artikkel i tidsskrift (Fagfellevurdert)
  • 24.
    Magnuson, Martin
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik II.
    Butorin, Sergei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Fysik II.
    Såthe, Conny
    Nordgren, Joseph
    Ravindran, P
    Spin transition in LaCoO3 investigated by resonant soft X-ray emission spectroscopy2004Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 68, nr 2, s. 289-295Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The spin transition in LaCoO3 is investigated by temperature-dependent resonant soft X-ray emission spectroscopy near the Co 2p absorption edges. This element-specific technique is more bulk sensitive with respect to the temperature-induced spin state of the Co3+ ions in LaCoO3 than other high-energy spectroscopic methods. The spin transition is interpreted and discussed with ab initio density-functional theory within the fixed-spin moment method, which is found to yield consistent spectral functions to the experimental data. The spectral changes for LaCoO3 as a function of temperature suggest a change in spin state as the temperature is raised from 85 to 300 K, while the system remains in the same spin state as the temperature is further increased to 510 K.

  • 25.
    Mathieu, Roland
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    De Toro, J. A.
    Salazar, D.
    Lee, S. S.
    Cheong, J. L.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Phase transition in a super superspin glass2013Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 102, nr 6, s. 67002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We here confirm the occurrence of spin glass phase transition and extract estimates of associated critical exponents of a highly monodisperse and densely compacted system of bare maghemite nanoparticles. This system has earlier been found to behave like an archetypal spin glass, with, e.g., a sharp transition from paramagnetic to non-equilibrium behavior, suggesting that this system undergoes a spin glass phase transition at a relatively high temperature, T-g similar to 140K. 

  • 26.
    Mathieu, Roland
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    He, J. P.
    Yu, X. Z.
    Kaneko, Y.
    Uchida, M.
    Lee, Y. S.
    Arima, T.
    Asamitsu, A.
    Tokura, Y.
    Coexistence of long-ranged charge- and orbital order and spin-glas state in single-layered manganites with weak quenched disorder2007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 80, s. 37001-Artikkel i tidsskrift (Fagfellevurdert)
  • 27.
    Mathieu, Roland
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Hudl, Matthias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Nordblad, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Memory and rejuvenation in a spin glass2010Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 90, nr 6, s. 67003-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The temperature dependence of the magnetisation of a Cu(Mn) spin glass (T-g approximate to 57 K) has been investigated using weak probing magnetic fields (H = 0.5 or 0 Oe) and specific thermal protocols. The behaviour of the zero-field-cooled, thermoremanent and isothermal remanent magnetisation on (re-) cooling the system from a temperature (40K) where the system has been aged is investigated. It is observed that the measured magnetisation is formed by two parts: i) a temperature- and observation time-dependent thermally activated relaxational part governed by the age- and temperature-dependent response function and the (latest) field change made at a lower temperature, superposed on ii) a weakly temperature-dependent frozen-in part. Interestingly we observe that the spin configuration that is imprinted during an elongated halt in the cooling, if it is accompanied by a field-induced magnetisation, also includes a unidirectional excess magnetisation that is recovered on returning to the ageing temperature.

  • 28. Mendonca, J. T.
    et al.
    Thidé, Bo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Neutrino orbital angular momentum in a plasma vortex2008Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 84, nr 4, s. 41001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is shown that an electron-neutrino beam, propagating in a background plasma, can be decomposed into orbital momentum (OAM) states, similar to the OAM photon states. Coupling between different OAM neutrino states, in the presence of a plasma vortex, is considered. We show that plasma vorticity can be transfered to the neutrino beam, which is relevant to the understanding of the neutrino sources in astrophysics. Observation of neutrino OAM states could eventually become possible.

  • 29. Moskalenko, S. A.
    et al.
    Liberman, M. A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Podlesny, I. V.
    On the theory of two-dimensional combined magnetoexciton-cyclotron resonances2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 85, nr 5, s. 57002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A theory of combined exciton-cyclotron resonance in the quantum well structures is developed for a strong magnetic field. The absorption band structure is calculated for optical quantum transitions with circularly polarized radiation creating a two-dimensional exciton and simultaneously exciting one of the resident electrons from the lowest to the first Landau level. The dipole-active transitions are considered in the second-order perturbation theory taking into account as perturbations the electron-photon interaction and the electron-electron Coulomb interaction. In agreement with the experimental observation it is shown that for sigma(-) polarized light the probability of quantum transition is four times larger than for sigma(+) light polarization. Copyright (C) EPLA, 2009

  • 30.
    Nabi, Z
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Kondenserade materiens teori (Fysik IV).
    Ahuja, R
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Kondenserade materiens teori (Fysik IV).
    Ferromagnetism in (Mn,Li) co-doped CdSe2008Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 84, nr 5, s. 57012-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ab initio calculations based on the density functional theory are reported for the Mn-doped CdSe for 5.5% and 12.5% Mn on a Cd sublattice. It is found that Mn-doped CdSe is antiferromagnetic. An essential ingredient to stabilize the ferromagnetism in bulk Cd1-x MnxSe can be realized by the co-doping of Li. We demonstrate that CdSe co-doped with Mn and Li has a stable ferromagnetic ground state and we show that the electronic structure of Cd1-2xMnxLixSe has a nearly metallic character.

  • 31.
    Niklasson, Gunnar A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Niklasson, Maria H.
    Musikinstitutet Betel, Bromma Folkhögskola.
    Non-Gaussian distributions of melodic intervals in music: The Lévy-stable approximation2015Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 112, nr 4, artikkel-id 40003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The analysis of structural patterns in music is of interest in order to increase ourfundamental understanding of music, as well as for devising algorithms for computer-generatedmusic, so called algorithmic composition. Musical melodies can be analyzed in terms of a “music walk” between the pitches of successive tones in a notescript, in analogy with the “random walk”model commonly used in physics. We find that the distribution of melodic intervals between tones can be approximated with a L´evy-stable distribution. Since music also exibits self-affine scaling,we propose that the “music walk” should be modelled as a L´evy motion. We find that the L´evy motion model captures basic structural patterns in classical as well as in folk music.

  • 32.
    Nisar, J
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Scheicher, Ralph H.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Peng, X
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Stability of ferromagnetic phase in Fe-doped AlH32009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 85, nr 6, s. 67006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have carried out a systematic theoretical investigation of Fe-doped AlH3 to study its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All calculations were performed using the projector augmented-wave method and generalized-gradient approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at 1.1 mu(B) per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms varying from 3.25 angstrom to 7.41 angstrom. We conclude that the ferromagnetic phase in Fe-doped AlH3 is stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due to the holes created by Fe-doping and the larger level splitting of the interacting gap states within the ferromagnetic phase. Copyright (C) EPLA, 2009

  • 33.
    Nisar, Jawad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Peng, Xiangyang
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Kang, T. W.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Stabilizing the defect-induced dilute magnetic semiconductors: Li-doping in GaN with Ga vacancies2011Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 93, nr 5, s. 57006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By means of first-principles calculations, we have investigated the effects of various Li-doping on the exchange interaction and the formation energy in bulk GaN with Ga vacancies. Although the Ga vacancies can induce ferromagnetism in GaN, their formation energy is rather high. Our calculations show that Li-doping can effectively tune the formation energy of Ga vacancies. It is revealed that the stabilizing effect depends on whether the number of holes is increased or decreased after Li-doping. When Li atoms substitutes for N atoms or occupies the interstitial sites, the holes are reduced and the formation energy of Ga vacancies is lowered. In contrast, Li substituting for Ga generates additional holes in the system, leading to an enhancement of the formation energy of Ga vacancies and making the system less stable.

  • 34.
    NORDBLAD, P
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    LUNDGREN, L
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    SANDLUND, L
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    FIELD-DEPENDENCE OF THE REMANENT MAGNETIZATION IN SPIN-GLASSES1987Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 3, s. 235-241Artikkel i tidsskrift (Fagfellevurdert)
  • 35.
    Phuyal, Dibya
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Mukherjee, Soham
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Das, Shyamashis
    Department of Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India.
    Jana, Somnath
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Kvashnina, Kristina O.
    Rossendorf Beamline at ESRF - The European Synchrotron - CS40220, 38043 Grenoble Cedex 9, France; Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology - PO Box 510119, 01314 Dresden, Germany.
    Sarma, D.D.
    Department of Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India.
    Rensmo, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Butorin, Sergei M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Karis, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    The origin of low bandgap and ferroelectricity of a co-doped BaTiO32018Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 124, nr 2, artikkel-id 27005Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We recently demonstrated the lowest bandgap bulk ferroelectric material, BaTi1-x(Mn1/2Nb1/2)xO3, a promising candidate material for visible light absorption in opto- electronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound’s electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates with our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K-edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.

  • 36.
    Ramzan, Muhammad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ahuja, R
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ferromagnetism in the potential cathode material LiNaFePO4F2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 87, nr 1, s. 18001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the ab initio study of the cathode material LiNaFePO4F, which is suitable for rechargeable batteries. Our calculations reveal the ferromagnetic order to be the ground state of this material. We also predict more than 5.0V intercalation voltage of this material for sodium-ion batteries. The low cost of sodium iron. fluorophasphate batteries and more than 5.0V intercalation voltage makes it the more suitable candidate, commercially and scientifically, than any other cathode materials for rechargeable batteries. Copyright (C) EPLA, 2009

  • 37. Rappolt, M.
    et al.
    Di Gregorio, G.M.
    Almgren, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi. Avdelningen för fysikalisk kemi.
    Amenitsch, H.
    Pabst, G.
    Laggner, P.
    Mariani, P.
    Non-equilibrium formation of the cubic Pn3m phase in a monoolein/water system2006Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 75, nr 2, s. 267-273Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Time-resolved small-angle X-ray diffraction experiments have been carried out to investigate the transformation from the cubic gyroid Ia3d to the cubic diamond Pn3m phase. The transition was induced by rapid addition of water to a monoolein/water system changing the initial water concentration of 26% w/w to excess of water conditions. The transformation proceeds in two steps: at the beginning, the two cubic mesophases have a strongly differing lipid/water composition and are accompanied by an intermediate phase. This phase vanishes as the ratio of cell parameters exceeds 1.50. Thereafter, the transition continues by a direct nearly isoareal transformation of the cubic minimal surfaces. Lateral area per lipid molecule, molecular shape and principle curvatures are about the same in this regime.

  • 38. Remhof, A.
    et al.
    Nowak, G.
    Zabel, H.
    Björck, Matts
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Pärnaste, Martin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Uzdin, V.
    Remote control of the Fe magnetic moment in magnetic heterostructures2007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 79, nr 3, s. 37003-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In magnetic superlattices with interlayer exchange coupling, not only the coupling strength but also the magnetic moment of the ferromagnetic layer can be altered non-locally by modifying the electronic structure of the non-magnetic spacer layer. Specifically, changes of the electronic structure of the V spacer layers in Fe/V (001) superlattices are seen to affect the adjacent Fe layers. By reversibly loading the V layer with hydrogen, the magnetic moment of Fe increases, whereas the induced magnetic moment in V remains unchanged. The nature of this remote and non-local control of the magnetic moment is connected with a d-electron charge transfer and effective shift of the Fermi level relative to the d-bands of Fe and V, as elucidated on the basis of self-consistent electronic structure calculations.

  • 39. Sa, B.
    et al.
    Zhou, J.
    Sun, Z.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Strain-induced topological insulating behavior in ternary chalcogenide Ge2Sb2Te52012Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, nr 2, s. 27003-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We unraveled the strain-induced topological insulating behavior in Ge2Sb2Te5 (GST) by means of ab initio calculations. The semiconductor-to-topological-insulator (TI) transition of Ge2Sb2Te5 were induced by the strains along the < 100 > and < 110 > direction as well as the shear strains. Ge2Sb2Te5 exhibits three types of TI-characterized conducting surface states: the single Dirac cone feature, the odd band-type and the Bi2Se3-type. The physical origin of the semiconductor-TI transition is the strain-induced inversion of the characterizations of conduction band minimum and valence band maximum with spin-orbit coupling. The present results suggest that GST-related materials are a new family of strain-induced TI.

  • 40.
    Sagynbaeva, Myskal
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Hussain, Tanveer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Panigrahi, Puspamitra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Johansson, Börje
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Complementing the adsorption energies of CO2, H2S and NO2 to h-BN sheets by doping with carbon2015Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 109, nr 5, artikkel-id 57008Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We predict the adsorption proficiency of hexagonal boron nitride (h-BN) sheets to toxic gas molecules like CO2, H2S and NO2 on the basis of first-principles density functional theory calculations. The computed energies predict the pristine h-BN sheet to have very little affinity towards the mentioned gas molecules. However, while doping C at the N site of the h-BN sheet brings a significant enhancement to the estimated adsorption energies, doping C at B site of the sheet is found to be energetically not so favorable. To have a higher coverage effect, the concentration of C doping on the h-BN sheet is further increased which resulted in upsurging the adsorption energies for the mentioned gas molecules. Among the three, CO2, H2S are found to be physisorbed to the C-doped h-BN sheets, where as the C-doped sheets are found to have strong affinity towards NO2 gas molecules.

  • 41. Schulz, J.
    et al.
    Loos, E.
    Huttula, M.
    Heinaesmaeki, S.
    Svensson, S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Aksela, S.
    Aksela, H.
    A method to characterize electronic states of 4s ionized Rb by combined laser and synchrotron spectroscopy2008Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 83, nr 5, s. 53001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photoelectron studies of laser-excited atomic states can reveal more information about the final ionic states than ground-state photoemission. The possibility to tune the laser to distinct fine-structure sub-states of the excited states allows to select specific angular-momentum couplings of the valence electron that are conserved during photoemission. In the 4s photoemission of laser-excited rubidium we use this method to determine the final-state energies and widths of doubly excited ionic states and characterize the angular-momentum couplings.

  • 42.
    Sjöqvist, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen, Avdelningen för kvantkemi.
    Experimentally testable geometric phase of sequences of Everett's relative quantum states2009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 86, s. 30005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Everett's concept of relative state is used to introduce a geometric phase that depends nontrivially on entanglement in a pure quantum state. We show that this phase can be measured in multiparticle interferometry. A correlation-dependent generalization of the relative state geometric phase to mixed quantum states is outlined.

  • 43. Sorriso-Valvo, L.
    et al.
    Yordanova, Emiliya
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Carbone, V.
    On the scaling properties of anisotropy of interplanetary magnetic turbulent fluctuations2010Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 90, nr 5, s. 59001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The anisotropic character of interplanetary magnetic-field turbulence has been studied through the analysis of Cluster data. The full tensor of the mixed second-order structure functions has been used to quatitatively measure the degree of anisotropy and its effect on small-scale turbulence. Three different regions of the near-Earth space have been studied, namely the solar wind, the Earth's foreshock and magnetosheath. While in the undisturbed solar wind the observed strong anisotropy is mainly due to the large-scale magnetic field, near the magnetosphere other sources of anisotropy influence the magnetic-field properties.

  • 44.
    Souvatzis, Petros
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Arapan, Sergiu
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Katsnelson, M. I.
    Temperature-driven alpha-to-beta phase transformation in Ti, Zr and Hf from first-principles theory combined with lattice dynamics2011Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 96, nr 6, s. 66006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lattice dynamical methods used to predict phase transformations in crystals typically deal with harmonic phonon spectra and are therefore not applicable in important situations where one of the competing crystal structures is unstable in the harmonic approximation, such as the bcc structure involved in the hcp-to-bcc martensitic phase transformation in Ti, Zr and Hf. Here we present an expression for the free energy that does not suffer from such shortcomings, and we show by self-consistent ab initio lattice dynamical calculations (SCAILD), that the critical temperature for the hcp-to-bcc phase transformation in Ti, Zr and Hf, can be effectively calculated from the free-energy difference between the two phases. This opens up the possibility to study quantitatively, from first-principles theory, temperature-induced phase transitions.

  • 45.
    Stasiewicz, K.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Markidis, S.
    Eliasson, B.
    Strumik, M.
    Yamauchi, M.
    Acceleration of solar wind ions to 1 MeV by electromagnetic structures upstream of the Earth's bow shock2013Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 102, nr 4, s. 49001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present measurements from the ESA/NASA Cluster mission that show in situ acceleration of ions to energies of 1MeV outside the bow shock. The observed heating can be associated with the presence of electromagnetic structures with strong spatial gradients of the electric field that lead to ion gyro-phase breaking and to the onset of chaos in ion trajectories. It results in rapid, stochastic acceleration of ions in the direction perpendicular to the ambient magnetic field. The electric potential of the structures can be compared to a field of moguls on a ski slope, capable of accelerating and ejecting the fast running skiers out of piste. This mechanism may represent the universal mechanism for perpendicular acceleration and heating of ions in the magnetosphere, the solar corona and in astrophysical plasmas. This is also a basic mechanism that can limit steepening of nonlinear electromagnetic structures at shocks and foreshocks in collisionless plasmas. 

  • 46.
    SVEDLINDH, P
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    LUNDGREN, L
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    NORDBLAD, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    CHEN, HS
    Bell.
    DYNAMIC SCALING IN AN AMORPHOUS METALLIC SPIN-GLASS1987Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 3, s. 243-249Artikkel i tidsskrift (Fagfellevurdert)
  • 47.
    SVEDLINDH, P
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    LUNDGREN, L
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    NORDBLAD, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    CHEN, HS
    Bell.
    STATIC SCALING IN AN AMORPHOUS METALLIC SPIN-GLASS1986Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 2, s. 805-812Artikkel i tidsskrift (Fagfellevurdert)
  • 48. Tamburini, F.
    et al.
    Sponselli, A.
    Thidé, Bo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Mendonca, J. T.
    Photon orbital angular momentum and mass in a plasma vortex2010Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 90, nr 4, s. 45001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We analyse the Anderson-Higgs mechanism of photon mass acquisition in a plasma and study the contribution to the mass from the orbital angular momentum acquired by a beam of photons when it crosses a spatially structured charge distribution. To this end we apply Proca-Maxwell equations in a static plasma with a particular spatial distribution of free charges, notably a plasma vortex, that is able to impose orbital angular momentum (OAM) onto light. In addition to the mass acquisition of the conventional Anderson-Higgs mechanism, we find that the photon acquires an additional mass from the OAM and that this mass reduces the Proca photon mass.

  • 49. Tamburini, F.
    et al.
    Thidé, Bo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Storming Majorana's Tower with OAM states of light in a plasma2011Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 96, nr 6, s. 64005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We extend the relationship between mass and spin angular momentum, described by the bosonic spectrum of positive definite mass particles of the Majorana solution to the Dirac equation, to photons that acquire an effective Proca mass through the Anderson-Higgs mechanism (Anderson P. W., Phys. Rev., 130 (1963) 439) when they propagate in a plasma. In an earlier paper (TAMBURINI F. et al., EPL, 90 (2010) 45001) we showed that if the plasma is structured, it can impart orbital angular momentum (OAM) to the photons that reduces the total Proca photon mass. Here we show, through a generalisation of Majorana's solution, that photons with OAM in a plasma cannot assume negative squared mass states. This means that there exist interesting analogies with Quantum Gravity or General Relativity models involving a modified action of the Lorentz group.

  • 50.
    Yordanova, Emiliya
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutet för rymdfysik, Uppsalaavdelningen.
    Perri, S.
    Sorriso-Valvo, L.
    Carbone, V.
    Multipoint observation of anisotropy and intermittency in solar-wind turbulence2015Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 110, nr 1, artikkel-id 19001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using high-resolution magnetic-field Cluster observations, we have investigated the magnetic-field anisotropy via the second-and fourth-order structure functions over a wide range of scales reaching below the subproton scale. The magnetic-field increments have been computed from single-and two-spacecraft measurements. The two-satellite technique allows us to study the increments as a function of an actual space lag. Both single-and two-point analyses show that the magnetic field is anisotropic even at small time/spatial scales. The single-spacecraft data also shows that the degree of anisotropy does not change with the scale at proton and subproton scales. It is also pointed out that the degree of magnetic-field anisotropy tends to be overestimated in the single-spacecraft data analysis. This is particularly evident at small scales and it depends on the angle between the spacecraft separation and the flow direction. From the fourth-order moment of the probability density function of the magnetic-field increments we have also investigated the presence of intermittency in the fluctuations. Even though to a different degree, intermittency was present over the entire range of scales, with an indication of scale invariance at subproton scales.

12 1 - 50 of 51
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