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  • 1.
    Alfredsson, Svante
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Högberg, Jia Li
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    A closed-form solution to statically indeterminate adhesive joint problems — exemplified on ELS-specimens2008Ingår i: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 28, nr 7, s. 350-361Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A beam/adhesive-layer model is developed. For this model a closed-form solution method applicable to arbitrary boundary conditions is presented. This enables the solution of a large number of practical problems which may be statically indeterminate. The stress state in the adhesive layer and the adherends of the beam/adhesive-layer model is also scrutinized. The method is exemplified in an analysis of the end-loaded split (ELS) specimen, commonly used to determine fracture energies of adhesive layers. The effect of the flexibility of the adhesive layer on the energy release rate and the critical crack length for stable crack growth is examined. Both symmetric and unsymmetric ELS-specimens are studied.

  • 2.
    Aryasetiawan, F.
    et al.
    Department of Physics, Division of Mathematical Physics, Lund University, Lund, Sweden.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Miyake, T.
    CD-FMat, AIST, Tsukuba, Japan / ESICMM, National Institute for Materials Science, Tsukuba, Japan.
    Green's function theory of orbital magnetic moment of interacting electrons in solids2016Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 93, nr 16, artikel-id 161104(R)Artikel i tidskrift (Refereegranskat)
  • 3.
    Aryasetiawan, Ferdi
    et al.
    Department of Physics, Division of Mathematical Physics, Lund University, Lund, Sweden.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Modern theory of orbital magnetic moment in solids2019Ingår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 128, s. 87-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The magnetic moment in a solid is usually associated with the electron spins but there is an additional contribution due to the orbital motion of the electrons. For a finite system such as an atom or molecule the orbital moment can be readily calculated. However, for a periodic system the formula used for finite systems becomes ill-defined due to the presence of the position operator. In the last decade a modern theory of orbital magnetization that allows for a rigorous calculation of the magnetic moment of periodic crystals has been developed. This article provides a survey of the theoretical development of this new topic as well as recent, albeit a few, applications of the new formula to real materials. Although the original theory was worked out for non-interacting systems, there has been recent progress in the theory of orbital magnetic moment of interacting electrons in solids. To include the effects of electron-electron interactions two approaches have been proposed, one based on current spin density functional theory and another on the many-body Green's function method. The two approaches are very different but both methods provide convenient yet rigorous means of including the effects of exchange and correlations beyond the commonly used local density approximation of density functional theory.

  • 4.
    Di Marco, I.
    et al.
    Uppsala University, Sweden.
    Thunström, P.
    Uppsala University, Sweden / Institute for Solid State Physics, Vienna University of Technology, Austria.
    Katsnelson, M. I.
    Radboud University Nijmegen, The Netherlands.
    Sadowski, J.
    Polish Academy of Sciences, Poland / Lund University, Sweden.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för vård och natur.
    Lebegue, S.
    Institut Jean Barriol, Université de Lorraine, France.
    Kanski, J.
    Chalmers University of Technology, Sweden.
    Eriksson, O.
    Uppsala University, Sweden.
    Electron correlations in MnxGa1-xAs as seen by resonant electron spectroscopy and dynamical mean field theory2013Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 4, artikel-id 2645Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    After two decades since the discovery of ferromagnetism in manganese-doped gallium arsenide, its origin is still debated, and many doubts are related to the electronic structure. Here we report an experimental and theoretical study of the valence electron spectrum of manganese-doped gallium arsenide. The experimental data are obtained through the differences between off- and on-resonance photo emission data. The theoretical spectrum is calculated by means of a combination of density-functional theory in the local density approximation and dynamical mean field theory, using exact diagonalization as impurity solver. Theory is found to accurately reproduce measured data and illustrates the importance of correlation effects. Our results demonstrate that the manganese states extend over a broad range of energy, including the top of the valence band, and that no impurity band splits-off from the valence band edge, whereas the induced holes seem located primarily around the manganese impurity.

  • 5.
    Högberg, J. Li
    et al.
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Sørensen, B. F.
    Tech Univ Denmark, Mat Res Dept, Riso Natl Lab, DK-4000 Roskilde, Denmark.
    Stigh, Ulf
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Constitutive behaviour of mixed mode loaded adhesive layer2007Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 44, nr 25-26, s. 8335-8354Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mixed mode testing of adhesive layer is performed with the Mixed mode double Cantilever Beam specimen. During the experiments, the specimens are loaded by transversal and/or shear forces; seven different mode mixities are tested. The J-integral is used to evaluate the energy dissipation in the failure process zone. The constitutive behaviour of the adhesive layer is obtained by a so called inverse method and fitting an existing mixed mode cohesive model, which uses a coupled formulation to describe a mode dependent constitutive behaviour. The cohesive parameters are determined by optimizing the parameters of the cohesive model to the experimental data. A comparison is made with the results of two fitting procedures. It is concluded that the constitutive properties are coupled, i.e. the peel and shear stress depend on both the peel and shear deformations. Moreover, the experiments show that the critical deformation in the peel direction is virtually independent of the mode mixity.

  • 6.
    Högberg, Jia Li
    Högskolan i Skövde, Institutionen för teknik och samhälle.
    Unbalanced UCB-specimen2006Ingår i: CDCM06 online proceedings, University of Stuttgart , 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Double Cantilever Beam (DCB) specimen is a common test geometry for testing of mode I fracture properties of adhesive joints. However, when unbalances are introduced to the adherends, the adhesive layer is loaded in a combination of peel (mode I) and shear (mode II). In this work the unbalanced DCB-specimen is studied by the use of the beam/adhesive layer (B/A) model, in which the adherends are considered as beams and the adhesive layer as a generalised spring media. The effect of the thickness of adhesive layer together with the effect of the geometrical and material unbalances is analysed. The result of the B/A model is compared to the continuum model through FE-simulations. Finally, an unsymmetric DCB-specimen is dimensioned for mixed mode testing of adhesive layer.

  • 7.
    Kanski, Janusz
    et al.
    Chalmers University of Technology, Göteborg, Sweden.
    Ilver, Lars
    Chalmers University of Technology, Göteborg, Sweden.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Ulfat, Intikhab
    Department of Physics, University of Karachi, Pakistan.
    Leandersson, Mats
    MAX IV Laboratory, Lund University, Lund, Sweden.
    Sadowski, Janusz
    MAX-IV laboratory, Lund University, Lund, Sweden / Institute of Physics, Polish Academy of Sciences, Warszawa, Poland.
    Di Marco, Igor
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Electronic structure of (Ga,Mn)As revisited2017Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 19, nr 2, s. 1-8, artikel-id 023006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The detailed nature of electronic states mediating ferromagnetic coupling in dilute magnetic semiconductors, specifically (Ga,Mn)As, has been an issue of long debate. Two confronting models have been discussed emphasizing host band vs. impurity band carriers. Using angle resolved photoemission we show that the electronic structure of the (Ga,Mn)As system is significantly modified from that of GaAs throughout the valence band. Close to the Fermi energy, the presence of Mn induces a strong mixing of the bulk bands of GaAs, which results in the appearance of a highly dispersive band in the gap region of GaAs.

    For Mn concentrations above 1% the band reaches the Fermi level, and can thus host the delocalized holes needed for ferromagnetic coupling. Overall, our data provide a firm evidence of delocalized carriers belonging to the modified host valence band.

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  • 8.
    Nilsson, Fredrik
    et al.
    Lund University.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Aryasetiawan, Ferdi
    Lund University.
    Dynamically screened Coulomb interaction in the parent compounds of hole-doped cuprates: Trends and exceptions2019Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 99, nr 7, s. 1-9, artikel-id 075135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Although cuprate high-temperature superconductors were discovered already in 1986 the origin of the pairing mechanism remains elusive. While the doped compounds are superconducting with high transition temperatures T-c, the undoped compounds are insulating due to the strong effective Coulomb interaction between the Cu 3d holes. We investigate the dependence of the maximum superconducting transition temperature T-cmax on the on-site effective Coulomb interaction U using the constrained random-phase approximation. We focus on the commonly used one-band model of the cuprates, including only the antibonding combination of the Cu d(x2-y2) and O p(x) and p(y) orbitals and find a screening-dependent trend between the static value of U and T-cmax for the parent compounds of a large number of hole-doped cuprates. Our results suggest that superconductivity may be favored by a large on-site Coulomb repulsion. We analyze both the trend in the static value of U and its frequency dependence in detail and, by comparing our results to other works, speculate on the mechanisms behind the trend.

    Ladda ner fulltext (pdf)
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  • 9.
    Sjöstrand, Tor J.
    et al.
    Department of Physics, Division of Mathematical Physics, Lund University, Sweden.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Aryasetiawan, Ferdi
    Department of Physics, Division of Mathematical Physics, Lund University, Sweden.
    Influence of correlations on the orbital magnetization of the spin-1/2 Haldane-Hubbard model2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 5, s. 054427-1-054427-8, artikel-id 054427Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Orbital magnetization is known empirically to play an important role in several magnetic phenomena, suchas permanent magnetism and ferromagnetic superconductivity. Within the recently developed “modern theoryof orbital magnetization,” theoretical insight has been gained into the nature of this often neglected contributionto magnetism but is based on an underlying mean-field approximation. From this theory, a few treatments haveemerged which also take into account correlations beyond the mean-field approximation. Here, we apply thes cheme developed in a previous work [F. Aryasetiawan et al., Phys. Rev. B 93, 161104(R) (2016)] to thespin- 1/2 Haldane-Hubbard model to investigate the effect of charge fluctuations on the orbital magnetizationwithin the GW approximation. Qualitatively, we are led to distinguish between two quite different situations:(i) When the lattice potential is larger than the nearest-neighbor hopping, the correlations are found to boostthe orbital magnetization. (ii) If the nearest-neighbor hopping is instead larger than the lattice potential, thecorrelations reduce the magnetization. The boost and reduction are identified to stem from interband andintraband correlations, respectively, and the relative importance of the two varies with the strength of the latticepotential. We finally study graphene with parameters obtained from first principles.

  • 10.
    Sottile, F.
    et al.
    Laboratoire des Solides Irradiés UMR, Palaiseau, France.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för naturvetenskap.
    Reining, L.
    Laboratoire des Solides Irradiés UMR, Palaiseau, France.
    Aryasetiawan, F.
    Research Institute for Computational Sciences (RICS), Japan.
    Macroscopic and microscopic components of exchange-correlation interactions2003Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 68, nr 20, s. 205112-205122, artikel-id 205112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider two commonly used approaches for the ab initio calculation of optical-absorption spectra, namely, many-body perturbation theory based on Green’s functions and time-dependent density-functional theory (TDDFT). The former leads to the two-particle Bethe-Salpeter equation that contains a screened electron-hole interaction. We approximate this interaction in various ways, and discuss in particular the results obtained for a local contact potential. This, in fact, allows us to straightforwardly make the link to the TDDFT approach, and to discuss the exchange-correlation kernel fxc that corresponds to the contact exciton. Our main results, illustrated in the examples of bulk silicon, GaAs, argon, and LiF, are the following. (i) The simple contact exciton model, used on top of an ab initio calculated band structure, yields reasonable absorption spectra. (ii) Qualitatively extremely different fxc can be derived approximatively from the same Bethe-Salpeter equation. These kernels can however yield very similar spectra. (iii) A static fxc, both with or without a long-range component, can create transitions in the quasiparticle gap. To the best of our knowledge, this is the first time that TDDFT has been shown to be able to reproduce bound excitons.

  • 11.
    Ulfat, I.
    et al.
    Department of Physics, University of Karachi, Pakistan.
    Kanski, J.
    Chalmers University of Technology, Göteborg, Sweden.
    Ilver, L.
    Chalmers University of Technology, Göteborg, Sweden.
    Sadowski, J.
    MAX-IV laboratory, Lund University, Sweden.
    Karlsson, Krister
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap. Högskolan i Skövde, Forskningscentrum för Virtuella system.
    Ernst, A.
    Max-Planck-Institut für Mikrostrukturphysik, Halle, Germany / Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, Germany.
    Sandratskii, L.
    Max-Planck-Institut für Mikrostrukturphysik, Halle, Germany.
    Effects of nonuniform Mn distribution in (Ga,Mn)As2014Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 89, nr 4, s. 1-5, artikel-id 045312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Resonant in situ photoemission from Mn 3d states in Ga(1−x)MnxAs is reported for Mn concentrations down to the very dilute level of 0.1%. Concentration-dependent spectral features are analyzed on the basis of first-principles calculations for systems with selected impurity positions as well as for random alloys. Effects of direct Mn-Mn interaction are found for concentrations as low as 2.5%, and are ascribed to statistical (nonuniform) distribution of Mn atoms.

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