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  • 1.
    Averkiev, NS
    et al.
    Russian Academy of Science.
    Golub, LE
    Russian Academy of Science.
    Willander, Magnus
    Chalmers.
    Spin relaxation anisotropy in two-dimensional semiconductor systems2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 12, p. R271-R283Article, review/survey (Refereed)
    Abstract [en]

    Spin relaxation is investigated theoretically in two-dimensional systems. Various semiconductor structures of both n and p types are studied in detail. The most important spin relaxation mechanisms are considered. The spin relaxation times are calculated taking into account the contributions to the spin-orbit interaction due to the bulk inversion asymmetry and to the structure inversion asymmetry. It is shown that in-plane anisotropy of electron spin relaxation appears in III-V asymmetrical heterostructures. This anisotropy may be controlled by external parameters, and the spin relaxation times differ by several orders of magnitude.

  • 2.
    Berggren, Karl-Fredrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tellander, Felix
    Lund Univ, Sweden.
    Yakymenko, Iryna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Basic modelling of transport in 2D wave-mechanical nanodots and billiards with balanced gain and loss mediated by complex potentials2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 20, article id 204003Article in journal (Refereed)
    Abstract [en]

    Non-Hermitian quantum mechanics with parity-time (PT) symmetry is presently gaining great interest, especially within the fields of photonics and optics. Here, we give a brief overview of low-dimensional semiconductor nanodevices using the example of a quantum dot with input and output leads, which are mimicked by imaginary potentials for gain and loss, and how wave functions, particle flow, coalescence of levels and associated breaking of PT symmetry may be analysed within such a framework. Special attention is given to the presence of exceptional points and symmetry breaking. Related features for musical string instruments and wolf-notes are outlined briefly with suggestions for further experiments.

    The full text will be freely available from 2019-04-26 16:47
  • 3.
    Berggren, Karl-Fredrik
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Yakymenko, Iryna
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    Nature of electron states and symmetry breaking in quantum point contacts according to the local spin density approximation2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 16Article in journal (Refereed)
    Abstract [en]

    Electron states and local magnetization in quantum point contacts (QPCs) with different geometries and applied gate voltages are examined for a model GaAs/AlGaAs device. Using the local spin density approximation (LSDA) we recover ferromagnetic spatially split solutions in the pinch-off regime as well as antisymmetric solutions that occur with decreasing gate voltage. These kinds of spin states, which may appear in a repeated fashion in the few-electron regime, are precursors to an extended ferromagnetic state that may be associated with the 0.7 conductance anomaly. We briefly comment on some recent experiments indicating the presence of bound states (Yoon et al 2007 Phys. Rev. Lett. 99 136805). We have not found any indication of such states but suggest that the accumulations of spin and charge at the two ends of a QPC and associated singlet and triplet states are relevant in this context. © 2008 IOP Publishing Ltd.

  • 4.
    Beyer, Jan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Wang, P. H.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Suraprapapich, S
    Department of Electrical and Computer Engineering, University of California at San Diego, La Jolla, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, USA .
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Effects of a longitudinal magnetic field on spin injection and detection in InAs/GaAs quantum dot structures2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 14, p. 145304-Article in journal (Refereed)
    Abstract [en]

    Effects of a longitudinal magnetic field on optical spin injection and detection in InAs/GaAs quantum dot (QD) structures are investigated by optical orientation spectroscopy. An increase in optical and spin polarization of the QDs is observed with increasing magnetic field in the range of 0-2 T, and is attributed to suppression of exciton spin depolarization within the QDs that is promoted by hyperfine interaction and anisotropic electron-hole exchange interaction. This leads to a corresponding enhancement in spin detection efficiency of the QDs by a factor of up to 2.5. At higher magnetic fields when these spin depolarization processes are quenched, electron spin polarization in anisotropic QD structures (such as double QDs that are preferably aligned along a specific crystallographic axis) still exhibits rather strong field dependence under non-resonant excitation. In contrast, such field dependence is practically absent in more "isotropic" QD structures (e.g. single QDs). We attribute the observed effect to stronger electron spin relaxation in the spin injectors (i.e. wetting layer and GaAs barriers) of the lower-symmetry QD structures, which also explains the lower spin injection efficiency observed in these structures.

  • 5.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Reaction mechanisms for on-surface synthesis of covalent nanostructures2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 8, p. 083002-Article, review/survey (Refereed)
    Abstract [en]

    In recent years, on-surface synthesis has become an increasingly popular strategy to form covalent nanostructures. The approach has great prospects for facilitating the manufacture of a range of fascinating materials with atomic precision. However, the on-surface reactions are enigmatic to control, currently restricting its bright perspectives and there is a great need to explore how the reactions are governed. The objective of this topical review is to summarize theoretical work that has focused on comprehending on-surface synthesis protocols through studies of reaction mechanisms.

  • 6.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Tu, C. W.
    Defects in dilute nitrides2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, p. S3027-S3035Article, review/survey (Refereed)
    Abstract [en]

    An overview of our present knowledge and understanding of defects in dilute nitrides will be provided and their important roles in determining the success of dilute nitrides for optoelectronic device applications will be underlined. A brief summary of experimental results of defects by various techniques reported so far in the literature will be given. Our recent results from optically detected magnetic resonance studies of grown-in non-radiative defects in Ga(In)NAs and Ga(Al, In)NP will be discussed in some detail, in an effort to provide chemical identification and experimental signatures of defects. Among them, intrinsic defects such as antisites and self-interstitials have been positively identified, and the effects of growth conditions, chemical compositions and post-growth processing on the formation of the defects were studied. The information retrieved from the experimental findings is expected to provide useful guidance for designing strategies to eliminate defects that are harmful to device performance.

  • 7.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Izadifard, M.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Xin, H.P.
    Tu, C.W.
    On a possible origin of the 2.87 eV optical transition in GaNP2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 2, p. 449-457Article in journal (Refereed)
    Abstract [en]

    Temperature dependent photoluminescence excitation spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered for the GaNxP1-x alloys. Whereas the appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with the N content in the alloys. This questions the possible association of this feature with an N-related localized state. On the basis of the results of temperature dependent measurements, it is concluded that the state involved has a non-Γ character. Excitation of the known N-related localized states via this state is found to be non-selective, unlike that between the N-related centres. The observed properties are shown to be barely consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the '2.87 eV' state as being due to either a t 2 component of the X3c (or L1c) CBM or a level arising from a complex of N and H (in some form) are also discussed. © 2006 IOP Publishing Ltd.

  • 8.
    Carlberg, M H
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Dynamics of self-interstitial structures in body-centred-cubic W studied by molecular dynamics simulation2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, no 1, p. 79-86Article in journal (Refereed)
    Abstract [en]

    This study concerns a molecular dynamics (MD) simulation, using the embedded-atom method (EAM), of the self-diffusion of an interstitial in the bcc metal tungsten (W) at 2000 K. It is found that the interstitial moves only along (111) diagonals and that the switches to other nonparallel directions take place through a two-dimensional process. The (011) dumb-bell is central to this process. Movement along the (111) diagonals takes place through (111) crowdions occupying 2-6 lattice sites. The probabilities of a direction switch and a move are 0.249 and 0.751, respectively. Translating the complicated movement mechanism into the simple picture of interstitial hopping between lattice points, the diffusion velocity is calculated to be 520 m s(-1), and the activation energy for the interstitial self-diffusion is calculated to be 0.54 eV/interstitial.

  • 9.
    Carlberg, M H
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Self-interstitial structures in body-centred-cubic W studied by molecular dynamics simulation1999In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 11, no 34, p. 6509-6514Article in journal (Refereed)
    Abstract [en]

    This paper reports a simulation study of the detailed structure of an interstitial in a body-centred-cubic (bcc) metal, tungsten (W), using molecular dynamics and the embedded-atom method. Several distinct configurations can be discerned, including the well-known split-interstitial [011] dumb-bell. The [111] crowdion is also observed, as is a set of similar, one-dimensional, defect configurations. These are grouped into a proposed classification scheme, in which the traditional crowdion is revealed as part of a whole family. The defect energies of the various configurations are computed, and comparisons are made with bce iron (Fe) results. The [011] dumb-bell is the energetically most favourable configuration in W. It is found to have a radius of approximately one W lattice constant, 3.16 Angstrom.

  • 10.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    A critical evaluation of GGA plus U modeling for atomic, electronic and magnetic structure of Cr2AlC, Cr2GaC and Cr2GeC2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 9, p. 095601-Article in journal (Refereed)
    Abstract [en]

    In this work we critically evaluate methods for treating electron correlation effects in multicomponent carbides using a GGA + U framework, addressing doubts from previous works on the usability of density functional theory in the design of magnetic MAX phases. We have studied the influence of the Hubbard U-parameter, applied to Cr 3d orbitals, on the calculated lattice parameters, magnetic moments, magnetic order, bulk modulus and electronic density of states of Cr2AlC, Cr2GaC and Cr2GeC. By considering non-, ferro-, and five different antiferromagnetic spin configurations, we show the importance of including a broad range of magnetic orders in the search for MAX phases with finite magnetic moments in the ground state. We show that when electron correlation is treated on the level of the generalized gradient approximation (U = 0 eV), the magnetic ground state of Cr(2)AC (A = Al, Ga, Ge) is in-plane antiferromagnetic with finite Cr local moments, and calculated lattice parameters and bulk modulus close to experimentally reported values. By comparing GGA and GGA + U results with experimental data we find that using a U-value larger than 1 eV results in structural parameters deviating strongly from experimentally observed values. Comparisons are also done with hybrid functional calculations (HSE06) resulting in an exchange splitting larger than what is obtained for a U-value of 2 eV. Our results suggest caution and that investigations need to involve several different magnetic orders before lack of magnetism in calculations are blamed on the exchange-correlation approximations in this class of magnetic MAX phases.

  • 11.
    Dahlqvist, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Jansson, Ulf
    Uppsala University, Sweden.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Influence of boron vacancies on phase stability, bonding and structure of MB2 (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) with AlB2 type structure2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 43, p. 435702-Article in journal (Refereed)
    Abstract [en]

    Transition metal diborides in hexagonal AlB2 type structure typically form stable MB2 phases for group IV elements (M = Ti, Zr, Hf). For group V (M = V, Nb, Ta) and group VI (M = Cr, Mo, W) the stability is reduced and an alternative hexagonal rhombohedral MB2 structure becomes more stable. In this work we investigate the effect of vacancies on the B-site in hexagonal MB2 and its influence on the phase stability and the structure for TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, CrB2, MoB2, and WB2 using first-principles calculations. Selected phases are also analyzed with respect to electronic and bonding properties. We identify trends showing that MB2 with M from group V and IV are stabilized when introducing B-vacancies, consistent with a decrease in the number of states at the Fermi level and by strengthening of the B-M interaction. The stabilization upon vacancy formation also increases when going from M in period 4 to period 6. For TiB2, ZrB2, and HfB2, introduction of B-vacancies have a destabilizing effect due to occupation of B-B antibonding orbitals close to the Fermi level and an increase in states at the Fermi level.

  • 12.
    Edvardsson, Sverker
    et al.
    Mittuniversitetet, Institutionen för informationsteknologi och medier.
    Ojamäe, L
    Thomas, John O
    A study of vibrational modes in Na(+)beta-Alumina by molecular-dynamics simulation1994In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 6, no 7, p. 1319-1332Article in journal (Refereed)
    Abstract [en]

    The vibrational properties of crystalline Na+ beta-alumina (Na1.22Al11O17.11) have been studied using the molecular dynamics simulation technique. The vibrational density of states was calculated from the velocity autocorrelation function, and the infrared spectrum from the dipole-dipole autocorrelation function. Knowledge of the vibrations in different crystallographic directions for the different atomic species facilitates the assignment of spectral peaks. The sodium in-plane vibrations are 59, 88 and 112 cm-1, and the out-of-plane vibrations are at 146 cm-1. The stoichiometric compound is also studied, and in this case the sodium in-plane vibrations are at 80 cm-1 and the out-of-plane vibrations at 140 cm-1. The density of states is used to calculate thermodynamic properties: heat capacity, entropy and internal and free energy. The values obtained at 300 K are C(upsilon) = 410 J K-1 mol-1, S(upsilon) = 300 J K-1 mol-1, U = 370 kJ mol-1 and F = 280 kJ mol 1. The heat capacity and entropy values are in good agreement with experiment, and thus strongly support the empirical force field used in the simulation

  • 13. Esmaeili, M.
    et al.
    Sabooni, M.
    Islam Azad Univ, Dept Phys, Shahrood Branch, Shahrood, Iran.
    Haratizadeh, H.
    Shahrood Univ Technol, Dept Phys, Shahrood, Iran.
    Paskov, Plamen
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Holtz, Per-Olof
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Kamiyama, S.
    Meijo Univ, Dept Elect & Elect Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Iwaya, M.
    Meijo Univ, Dept Elect & Elect Engn, Tempaku Ku, Nagoya, Aichi 468, Japan.
    Optical properties of GaN/AlGaN QW nanostructures with different well and barrier widths2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 35Article in journal (Refereed)
    Abstract [en]

    Optical properties of wurtzite AlGaN/GaN quantum well (QW) structures grown by molecular-beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates have been investigated by means of photoluminescence (PL) and time-resolved photoluminescence (TRPL) at low temperature. The PL spectra exhibit a blue-shifted emission of GaN/AlGaN QW nanostructures by decreasing the barrier width, in contrast to the arsenide system (Pabla A S et al 1993 Appl. Phys. Lett. 63 752). This behavior is attributed to a redistribution across the samples of the huge built-in electric field (several hundreds of kV cm(-1)) induced by the polarization difference between wells and barriers. The trend of the barrier width dependence of the internal polarization field is reproduced by using simple electrostatic arguments. In addition, the effect of well width variation on the optical transition and decay time of GaN multiple quantum wells (MQWs) have been investigated, and it has been shown that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN MQWs. The time-resolved PL spectra of 3 nm well MQWs reveal that the spectral peak position shifts toward lower energies as the decay time increases and becomes red-shifted at longer decay times.

  • 14.
    Fahlman, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Henze, S.K.M.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Tengstedt, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of hybrid interfaces for polymer-based electronics2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 18Article, review/survey (Refereed)
    Abstract [en]

    The fundamentals of the energy level alignment at anode and cathode electrodes in organic electronics are described. We focus on two different models that treat weakly interacting organic/metal (and organic/organic) interfaces: the induced density of interfacial states model and the so-called integer charge transfer model. The two models are compared and evaluated, mainly using photoelectron spectroscopy data of the energy level alignment of conjugated polymers and molecules at various organic/metal and organic/organic interfaces. We show that two different alignment regimes are generally observed: (i) vacuum level alignment, which corresponds to the lack of vacuum level offsets (Schottky-Mott limit) and hence the lack of charge transfer across the interface, and (ii) Fermi level pinning where the resulting work function of an organic/metal and organic/organic bilayer is independent of the substrate work function and an interface dipole is formed due to charge transfer across the interface. We argue that the experimental results are best described by the integer charge transfer model which predicts the vacuum level alignment when the substrate work function is above the positive charge transfer level and below the negative charge transfer level of the conjugated material. The model further predicts Fermi level pinning to the positive (negative) charge transfer level when the substrate work function is below (above) the positive (negative) charge transfer level. The nature of the integer charge transfer levels depend on the materials system: for conjugated large molecules and polymers, the integer charge transfer states are polarons or bipolarons, for small molecules' highest occupied and lowest unoccupied molecular orbitals and for crystalline systems, the relevant levels are the valence and conduction band edges. Finally, limits and further improvements to the integer charge transfer model are discussed as well as the impact on device design. © IOP Publishing Ltd.

  • 15.
    Freitas, Rafael R. Q.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. University of Federal Bahia, Brazil.
    de Brito Mota, F.
    University of Federal Bahia, Brazil.
    Rivelino, R.
    University of Federal Bahia, Brazil.
    de Castilho, C. M. C.
    University of Federal Bahia, Brazil; University of Federal Bahia, Brazil.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Spin-orbit-induced gap modification in buckled honeycomb XBi and XBi3 (X = B, Al, Ga, and In) sheets2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 48, p. 485306-Article in journal (Refereed)
    Abstract [en]

    The band structure and stability of XBi and XBi3 (X = B, Al, Ga, and In) single sheets are predicted using first-principles calculations. It is demonstrated that the band gap values of these new classes of two-dimensional (2D) materials depend on both the spin-orbit coupling (SOC) and type of group-III elements in these hetero-sheets. Thus, topological properties can be achieved, allowing for viable applications based on coherent spin transport at room temperature. The spin-orbit effects are proved to be essential to explain the tunability by group-III atoms. A clear effect of including SOC in the calculations is lifting the spin degeneracy of the bands at the Gamma point of the Brillouin zone. The nature of the band gaps, direct or indirect, is also tuned by SOC, and by the appropriate X element involved. It is observed that, in the case of XBi single sheets, band inversions naturally occur for GaBi and InBi, which exhibit band gap values around 172 meV. This indicates that these 2D materials are potential candidates for topological insulators. On the contrary, a similar type of band inversion, as obtained for the XBi, was not observed in the XBi3 band structure. In general, the calculations, taking into account SOC, reveal that some of these buckled sheets exhibit sizable gaps, making them suitable for applications in room-temperature spintronic devices.

  • 16.
    Furlan, Andrej
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jansson, Ulf
    Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Structure and bonding in amorphous iron carbide thin films2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 4, p. 045002-Article in journal (Refereed)
    Abstract [en]

    We investigate the amorphous structure, chemical bonding, and electrical properties ofmagnetron sputtered Fe1−xCx (0.21 < x < 0.72) thin films. X-ray, electron diffraction andtransmission electron microscopy show that the Fe1−xCx films are amorphousnanocomposites, consisting of a two-phase domain structure with Fe-rich carbidic FeCy , and acarbon-rich matrix. Pair distribution function analysis indicates a close-range order similar tothose of crystalline Fe3C carbides in all films with additional graphene-like structures at highcarbon content (71.8 at% C). From x-ray photoelectron spectroscopy measurements, we findthat the amorphous carbidic phase has a composition of 15–25 at% carbon that slightlyincreases with total carbon content. X-ray absorption spectra exhibit an increasing number ofunoccupied 3d states and a decreasing number of C 2p states as a function of carbon content.These changes signify a systematic redistribution in orbital occupation due to charge-transfereffects at the domain-size-dependent carbide/matrix interfaces. The four-point proberesistivity of the Fe1−xCx films increases exponentially with carbon content from ∼200μcm(x = 0.21) to ∼1200μcm (x = 0.72), and is found to depend on the total carbon contentrather than the composition of the carbide. Our findings open new possibilities for modifyingthe resistivity of amorphous thin film coatings based on transition metal carbides through thecontrol of amorphous domain structures.

  • 17.
    Furlan, Andrej
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jansson, Ulf
    Uppsala University, Sweden .
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 41, p. 415501-415512Article in journal (Refereed)
    Abstract [en]

    The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni1−xCx (0.05≤x≤0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiCy phase), instead of the expected rhombohedral-Ni3C. At low carbon content (4.9 at%), the thin film consists of hcp-NiCy nanocrystallites mixed with a smaller amount of fcc-NiCx. The average grain size is about10–20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiCy nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiCy and fcc-NiCx nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp2 hybridization, consistent with photoelectron spectra that show a decreasing amount of C–Ni phase with increasing carbon content. The Ni 3d–C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show thatthe resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.

  • 18.
    Gebhardt, T
    et al.
    Rhein Westfal TH Aachen.
    Music, D
    Rhein Westfal TH Aachen.
    Ekholm, Marcus
    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.
    Vitos, L
    Royal Institute Technology KTH.
    Dick, A
    Max Planck Institute Eisenforsch GmbH.
    Hickel, T
    Max Planck Institute Eisenforsch GmbH.
    Neugebauer, J
    Max Planck Institute Eisenforsch GmbH.
    Schneider, J M
    Rhein Westfal TH Aachen.
    The influence of additions of Al and Si on the lattice stability of fcc and hcp Fe-Mn random alloys2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 24, p. 246003-Article in journal (Refereed)
    Abstract [en]

    We have studied the influence of additions of Al and Si on the lattice stability of face-centred-cubic (fcc) versus hexagonal-closed-packed (hcp) Fe-Mn random alloys, considering the influence of magnetism below and above the fcc Neel temperature. Employing two different ab initio approaches with respect to basis sets and treatment of magnetic and chemical disorder, we are able to quantify the predictive power of the ab initio methods. We find that the addition of Al strongly stabilizes the fcc lattice independent of the regarded magnetic states. For Si a much stronger dependence on magnetism is observed. Compared to Al, almost no volume change is observed as Si is added to Fe-Mn, indicating that the electronic contributions are responsible for stabilization/destabilization of the fcc phase.

  • 19.
    Gebhardt, T.
    et al.
    Rhein Westfal TH Aachen.
    Music, D.
    Rhein Westfal TH Aachen.
    Hallstedt, B.
    Rhein Westfal TH Aachen.
    Ekholm, Marcus
    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.
    Vitos, L.
    Royal Institute of Technology.
    M. Schneider, J.
    Rhein Westfal TH Aachen.
    Ab initio lattice stability of fcc and hcp Fe-Mn random alloys2010In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 29, p. 295402-Article in journal (Refereed)
    Abstract [en]

    We have studied the lattice stability of face centred cubic (fcc) versus hexagonal close packed (hcp) Fe-Mn random alloys using ab initio calculations. In the calculations we considered the antiferromagnetic order of local moments, which for fcc alloys models the magnetic configuration of this phase at room temperature (below its Neel temperature) as well as their complete disorder, corresponding to paramagnetic fcc and hcp alloys. For both cases, the results are consistent with our thermodynamic calculations, obtained within the Calphad approach. For the room temperature magnetic configuration, the cross-over of the total energies of the hcp phase and the fcc phase of Fe-Mn alloys is at the expected Mn content, whereas for the magnetic configuration above the fcc Neel temperature, the hcp lattice is more stable within the whole composition range studied. The increase of the total energy difference between hcp and antiferromagnetic fcc due to additions of Mn as well as the stabilizing effect of antiferromagnetic ordering on the fcc phase are well displayed. These results are of relevance for understanding the deformation mechanisms of these random alloys.

  • 20.
    Hanke, Felix
    et al.
    Surface Science Research Centre, University of Liverpool, UK.
    Dyer, Matthew S.
    Surface Science Research Centre, University of Liverpool, UK.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Persson, Mats
    Surface Science Research Centre, University of Liverpool, UK.
    Structure and stability of weakly chemisorbed ethene adsorbed on low-index Cu surfaces: performance of density functionals with van der Waals interactions2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 42, p. 424217-424225Article in journal (Refereed)
    Abstract [en]

    We have investigated the performance of popular density functionals that include van der Waals interactions for the experimentally well-characterized problem of ethene (C(2)H(4)) adsorbed on the low-index surfaces of copper. This set of functionals does not only include three van der Waals density functionals-vdwDF-PBE, vdwDF-revPBE and optB86b-vdwDF-and two dispersion-corrected functionals-Grimme and TS-but also local and semi-local functionals such as LDA and PBE. The adsorption system of ethene on copper was chosen because it is a weakly chemisorbed system for which the vdW interactions are expected to give a significant contribution to the adsorption energy. Overall the density functionals that include vdW interactions increased substantially the adsorption energies compared to the PBE density functional but predicted the same adsorption sites and very similar C-C bonding distances except for two of the van der Waals functionals. The top adsorption site was predicted almost exclusively for all functionals on the (110), (100) and (111) surfaces, which is in agreement with experiment for the (110) surface but not for the (100) surface. On the (100) surface, all functionals except two van der Waals density functionals singled out the observed cross-hollow site from the calculated C-C bonding distances and adsorption heights. On the top sites on the (110) surface and the cross-hollow site on the Cu(100) surface, the ethene molecule was found to form a weak chemisorption bond. On the (111) surface, all functionals gave a C-C bonding distance and an adsorption height more typical for physisorption, in agreement with experiments.

  • 21.
    Ihnatsenka, Siarhei
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Zozoulenko, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Quantum wires in magnetic field: a comparative study of the Hartree-Fock and the spin density functional approaches2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 33Article in journal (Refereed)
    Abstract [en]

    We present a detailed comparison of the self-consistent calculations based on the Hartree-Fock and the spin density functional theory for a split-gate quantum wire in the IQH regime. We demonstrate that both approaches provide qualitatively (and, in most cases, quantitatively) similar results for the spin-resolved electron density, spin polarization, spatial spin separation at the edges and the effective g factor. Both approaches produce the same values of the magnetic fields corresponding to the successive subband depopulation and qualitatively similar evolution of the magnetosubbands. Quantitatively, however, the HF and the DFT subbands are different (even though the corresponding total electron densities are practically the same). In contrast to the HF approach, the DFT calculations predict much larger spatial spin separation near the wire edge for the low magnetic fields (when the compressible strips for spinless electrons are not formed yet). In the opposite limit of the large fields, the Hartree-Fock and the DFT approaches give very similar values for the spatial spin separation.

  • 22.
    Ingason, Arni Sigurdur
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Dahlqvist, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Magnetic MAX phases from theory and experiments: a review2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 43, p. 433003-Article, review/survey (Refereed)
    Abstract [en]

    This review presents MAX phases (M is a transition metal, A an A-group element, X is C or N), known for their unique combination of ceramic/metallic properties, as a recently uncovered family of novel magnetic nanolaminates. The first created magnetic MAX phases were predicted through evaluation of phase stability using density functional theory, and subsequently synthesized as heteroepitaxial thin films. All magnetic MAX phases reported to date, in bulk or thin film form, are based on Cr and/or Mn, and they include (Cr,Mn)(2)AlC, (Cr,Mn)(2)GeC, (Cr,Mn)(2)GaC, (Mo,Mn)(2)GaC, (V,Mn)(3)GaC2, Cr2AlC, Cr2GeC and Mn2GaC. A variety of magnetic properties have been found, such as ferromagnetic response well above room temperature and structural changes linked to magnetic anisotropy. In this paper, theoretical as well as experimental work performed on these materials to date is critically reviewed, in terms of methods used, results acquired, and conclusions drawn. Open questions concerning magnetic characteristics are discussed, and an outlook focused on new materials, superstructures, property tailoring and further synthesis and characterization is presented.

  • 23.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Academic Science, Hungary.
    Gali, Adam
    Hungarian Academic Science, Hungary; Budapest University of Technology and Econ, Hungary.
    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.
    Hybrid-DFT + V-w method for band structure calculation of semiconducting transition metal compounds: the case of cerium dioxide2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 45, article id 454002Article in journal (Refereed)
    Abstract [en]

    Hybrid functionals non-local exchange-correlation potential contains a derivative discontinuity that improves on standard semi-local density functional theory (DFT) band gaps. Moreover, by careful parameterization, hybrid functionals can provide self-interaction reduced description of selected states. On the other hand, the uniform description of all the electronic states of a given system is a known drawback of these functionals that causes varying accuracy in the description of states with different degrees of localization. This limitation can be remedied by the orbital dependent exact exchange extension of hybrid functionals; the hybrid-DFT + V-w method (Ivady et al 2014 Phys. Rev. B 90 035146). Based on the analogy of quasi-particle equations and hybrid-DFT single particle equations, here we demonstrate that parameters of hybrid-DFT + V-w functional can be determined from approximate theoretical quasi-particle spectra without any fitting to experiment. The proposed method is illustrated on the charge self-consistent electronic structure calculation for cerium dioxide where itinerant valence states interact with well-localized 4f atomic like states, making this system challenging for conventional methods, either hybrid-DFT or LDA + U, and therefore allowing for a demonstration of the advantages of the proposed scheme.

    The full text will be freely available from 2018-10-10 18:26
  • 24. Iwata, H.
    et al.
    Lindefelt, Ulf
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Oberg, S.
    Öberg, S., Department of Mathematics, Luleå University of Technology, SE-97187 Luleå, Sweden.
    Briddon, P.R.
    Department of Physics, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, United Kingdom.
    Theoretical study of planar defects in silicon carbide2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 48, p. 12733-12740Article in journal (Refereed)
    Abstract [en]

    We report on a theoretical investigation of extended planar defects in 3C-, 4H-, 6H-, and 15R-SiC which can be formed without breaking any bonds, covering a wide range of planar defects: twin boundaries, stacking faults, and polytype inclusions. Their electronic structures have been intensively studied using an ab initio supercell approach based on the density functional theory. Stacking fault energies are also calculated using both the supercell method and the axial next-nearest-neighbour Ising model. We discuss the electronic properties and energies of these defects in terms of the geometrical differences of stacking patterns.

  • 25.
    Jia, N
    et al.
    School of Materials and Metallurgy Northeastern University, Shenyang, PRC.
    Wang, Y D
    School of Materials and Metallurgy Northeastern university, Shenyang, PRC.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Micromechanical behaviors of duplex steel: in situ neutron diffraction measurements and simulations2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, p. 104259-104265Article in journal (Refereed)
  • 26.
    Jiang, Kaiyun
    et al.
    RWTH Aachen University, Germany.
    Music, Denis
    RWTH Aachen University, Germany.
    Sarakinos, Kostas
    Materials Chemistry, RWTH Aachen University, Germany.
    Schneider, Jochen M.
    RWTH Aachen University, Germany.
    Ab initio study of effects of substitutional additives on the phase stability of gamma-alumina2010In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 50, p. 505502-Article in journal (Refereed)
    Abstract [en]

    Using ab initio calculations, we have evaluated two structural descriptions of gamma-Al(2)O(3), spinel and tetragonal hausmannite, and explored the relative stability of gamma-Al(2)O(3) with respect to alpha-Al(2)O(3) with 2.5 at.% of Si, Cr, Ti, Sc, and Y additives to identify alloying element induced electronic structure changes that impede the gamma to alpha transition. The total energy calculations indicate that Si stabilizes gamma-Al(2)O(3), while Cr stabilizes alpha-Al(2)O(3). As Si is added, a bond length increase in alpha-Al(2)O(3) is observed, while strong and short Si-O bonds are formed in gamma-Al(2)O(3), consequently stabilizing this phase. On the other hand, Cr additions induce a smaller bond length increase in alpha-Al(2)O(3) than in gamma-Al(2)O(3), therefore stabilizing the a-phase. The bulk moduli of gamma-Al(2)O(3) with these additives show no significant changes. The phase stability and elastic property data discussed here underline the application potential of Si alloyed gamma-Al(2)O(3) for applications at elevated temperatures. Furthermore it is evident that the tetragonal hausmannite structure is a suitable description for gamma-Al(2)O(3).

  • 27.
    Johansson, Leif
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Virojanadara, Chariya
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Synchrotron radiation studies of the SiO2/SiC(0001) interface2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 33, p. S3423-S3434Article in journal (Refereed)
    Abstract [en]

    Two questions thought to have a significant effect on SiC-MOS device characteristics are treated. The existence of carbon clusters or carbon containing by-products and the existence of sub-oxides at the SiO2/SiC interface. Results of photoemission studies using synchrotron radiation of the interface of the Si-terminated surface of n-type SiC(0001) crystals are presented. The results show that no carbon clusters or carbon containing by-product can. be detected at the interface of in situ or ex situ grown samples with an oxide layer thickness larger than similar to10 Angstrom. The presence of sub-oxides at the SiO2/SiC interface was predicted in a theoretical calculation and has been revealed in Si 2p core level data by several groups. These results were not unanimous, significant differences in the number of sub-oxide and shifts were reported. A study also including the Si 1s core level and Si KLL Auger transitions was therefore made. These data show the presence of only one sub-oxide at the interface, assigned to Si1+ oxidation states. The SiO2 chemical shift is shown to exhibit a dependence on oxide thickness, similar to but smaller in magnitude than the thickness dependence earlier revealed for SiO2/Si.

  • 28.
    Johansson, Malin B.
    et al.
    Uppsala University, Sweden .
    Baldissera, Gustavo
    Royal Institute of Technology KTH, Stockholm, Sweden .
    Valyukh, Iryna
    Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.
    Persson, Clas
    Royal Institute of Technology KTH, Stockholm, Sweden .
    Arwin, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.
    Niklasson, Gunnar A.
    Uppsala University, Sweden .
    Osterlund, Lars
    Uppsala University, Sweden .
    Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 20, p. 205502-Article in journal (Refereed)
    Abstract [en]

    The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (P-tot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low P-tot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies E-g approximate to 3.1 eV, which increase with increasing P-tot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic delta-WO3, and monoclinic gamma- and epsilon-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The delta-WO3 and gamma-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (andgt;3 eV) and allowed transitions (andgt;3.8 eV). The calculations show that E-g in epsilon-WO3 is higher than in the delta-WO3 and gamma-WO3 phases, which provides an explanation for the P-tot dependence of the optical data.

  • 29.
    Karlsson, H.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Yakymenko, Iryna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nature of magnetization and lateral spin-orbit interaction in gated semiconductor nanowires2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 21, article id 215302Article in journal (Refereed)
    Abstract [en]

    Semiconductor nanowires are interesting candidates for realization of spintronics devices. In this paper we study electronic states and effects of lateral spin-orbit coupling (LSOC) in a one-dimensional asymmetrically biased nanowire using the Hartree-Fock method with Dirac interaction. We have shown that spin polarization can be triggered by LSOC at finite source-drain bias,as a result of numerical noise representing a random magnetic field due to wiring or a random background magnetic field by Earth magnetic field, for instance. The electrons spontaneously arrange into spin rows in the wire due to electron interactions leading to a finite spin polarization. The direction of polarization is, however, random at zero source-drain bias. We have found that LSOC has an effect on orientation of spin rows only in the case when source-drain bias is applied.

  • 30.
    Krasilnikov, O M
    et al.
    National Research Technology University of MISiS.
    Vekilov, Yu Kh
    National Research Technology University of MISiS.
    Mosyagin, I Yu
    National Research Technology University of MISiS.
    Isaev, Eyvas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Bondarenko, N G
    Uppsala University.
    Elastic phase transitions in metals at high pressures2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 19, p. 195402-Article in journal (Refereed)
    Abstract [en]

    The elastic phase transitions of cubic metals at high pressures are investigated within the framework of Landau theory. It is shown that at pressures comparable with the magnitude of the bulk modulus the phase transition is connected with the loss of stability relative to uniform deformation of the crystalline lattice. Discontinuity of the order parameter at the transition point and its equilibrium value are expressed through the second-to fourth-order elastic constants. The second-, third- and fourth-order elastic constants and phonon dispersion curves of vanadium under hydrostatic pressure are obtained by first-principles calculations. Structural transformation in vanadium under pressure is studied using the obtained results. It is shown that the experimentally observed at P approximate to 69 GPa phase transition in vanadium is the first-order phase transition close to a second-order phase transition.

  • 31.
    Kroon, Lars
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Järrendahl, Kenneth
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Neutral shielding and cloaking of magnetic fields using isotropic media2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 3Article in journal (Refereed)
    Abstract [en]

    A method for designing magnetic shields that do not perturb applied multipole fields in the static regime is developed. Cylindrical core-shell structures with two layers characterized by homogeneous isotropic permeabilities are found to support neutral shielding of multipole fields and unique cloaking solutions of arbitrary multipole order. An extra degree of freedom is provided by every layer added to the structure which may be exploited with an effective design formula for cloaking of additional field terms. The theory is illustrated with numerical simulations.

  • 32.
    Kurmaev, E. Z.
    et al.
    Russian Academy of Sciences - Ural Division, Yekaterinburg.
    Katsnelson, M. I.
    Russian Academy of Sciences - Ural Division, Yekaterinburg.
    Moeves, Alexander
    University of Saskatchewan, Saskatoon, Canada .
    Magnuson, Martin
    Uppsala University.
    Guo, J.-H.
    Uppsala University.
    Butorin, S. M.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Ederer, D. L.
    Tulane University, New Orleans.
    Iwami, M.
    Okayama University.
    Spectroscopic observation of polaron-lattice band structure in the conducting polymer polyaniline2001In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, no 17, p. 3907-3912Article in journal (Refereed)
    Abstract [en]

    We present the results of soft x-ray emission measurements for undoped and protonated polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed x-ray transitions. A finite spectral intensity of C Kα and N Kα XES is observed at the Fermi level for protonated polyemeraldine, supporting the applicability of the polaronic-metal model for highly conducting polymers.

  • 33.
    Lai, Chung-Chuan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Goyenola, Cecilia
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Näslund, Lars-Åke
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Gueorguiev, Gueorgui Kostov
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Synthesis and properties of CSxFy thin films deposited by reactive magnetron sputtering in an Ar/SF6 discharge2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 19, article id 195701Article in journal (Refereed)
    Abstract [en]

    A theoretical and experimental study on the growth and properties of a ternary carbon-based material, CSxFy, synthesized from SF6 and C as primary precursors is reported. The synthetic growth concept was applied to model the possible species resulting from the fragmentation of SF6 molecules and the recombination of S-F fragments with atomic C. The possible species were further evaluated for their contribution to the film growth. Corresponding solid CSxFy thin films were deposited by reactive direct current magnetron sputtering from a C target in a mixed Ar/SF6 discharge with different SF6 partial pressures (P-SF6). Properties of the films were determined by x-ray photoelectron spectroscopy, x-ray reflectivity, and nanoindentation. A reduced mass density in the CSxFy films is predicted due to incorporation of precursor species with a more pronounced steric effect, which also agrees with the low density values observed for the films. Increased P-SF6 leads to decreasing deposition rate and increasing density, as explained by enhanced fluorination and etching on the deposited surface by a larger concentration of F/F-2 species during the growth, as supported by an increment of the F relative content in the films. Mechanical properties indicating superelasticity were obtained from the film with lowest F content, implying a fullerene-like structure in CSxFy compounds.

  • 34.
    Lazić, Predrag
    et al.
    Massachusetts Institute of Technology, Cambridge, USA.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Herbert, F W
    Massachusetts Institute of Technology, Cambridge, USA.
    Chakraborty, Rupak
    Massachusetts Institute of Technology, Cambridge, USA.
    Sun, Ruoshi
    Massachusetts Institute of Technology, Cambridge, USA.
    Chan, M K Y
    Argonne National Laboratory, USA.
    Hartman, Katherine
    Massachusetts Institute of Technology, Cambridge, USA.
    Buonassisi, Tonio
    Massachusetts Institute of Technology, Cambridge, USA.
    Yildiz, Bilge
    Massachusetts Institute of Technology, Cambridge, USA.
    Ceder, Gerbrand
    Massachusetts Institute of Technology, Cambridge, USA.
    Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 46, p. 465801-Article in journal (Refereed)
    Abstract [en]

    Pyrite (FeS2), being a promising material for future solar technologies, has so far exhibited in experiments an open-circuit voltage (OCV) of around 0.2 V, which is much lower than the frequently quoted 'accepted' value for the fundamental bandgap of similar to 0.95 eV. Absorption experiments show large subgap absorption, commonly attributed to defects or structural disorder. However, computations using density functional theory with a semi-local functional predict that the bottom of the conduction band consists of a very low intensity sulfur p-band that may be easily overlooked in experiments because of the high intensity onset that appears 0.5 eV higher in energy. The intensity of absorption into the sulfur p-band is found to be of the same magnitude as contributions from defects and disorder. Our findings suggest the need to re-examine the value of the fundamental bandgap of pyrite presently in use in the literature. If the contribution from the p-band has so far been overlooked, the substantially lowered bandgap would partly explain the discrepancy with the OCV. Furthermore, we show that more states appear on the surface within the low energy sulfur p-band, which suggests a mechanism of thermalization into those states that would further prevent extracting electrons at higher energy levels through the surface. Finally, we speculate on whether misidentified states at the conduction band onset may be present in other materials.

  • 35.
    Lozovik, Yurii E
    et al.
    Russian Academy of Science.
    Berman, Oleg L
    Russian Academy of Science.
    Willander, Magnus
    Chalmers.
    Superfluidity of indirect excitons and biexcitons in coupled quantum wells and superlattices2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 47, p. 12457-12475Article in journal (Refereed)
    Abstract [en]

    The collective properties of indirect excitons in coupled quantum wells (CQWs) are considered. The energy of the ground state of the exciton liquid as a function of the density of electrons a and holes h at different separations D between a and h layers is analysed. The quantum gas-liquid transition as D decreases is studied. The superfluidity appearance temperatures in the system (Kosterlitz-Thouless transition temperatures) have been estimated at different separations D between a and h layers. For the anisotropic two-dimensional e-h system in CQWs the Mott metal-insulator quantum transition is considered. The instability of the ground state of the system of interacting two-dimensional indirect excitons in a slab of superlattice with alternating a and h layers is established. The stable system of indirect quasi-two-dimensional biexcitons, consisting of indirect excitons with opposite directed dipole moments, is considered. The radius and the binding energy of the indirect biexciton are calculated. The collective spectrum of a rare system of two-dimensional indirect biexcitons, interacting as electrical quadrupoles, is studied. The density of the superfluid component n(s) (T) and the Kosterlitz-Thouless phase transition to the superfluid state in this system are analysed.

  • 36.
    Magnuson, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Andersson, Matilda
    Uppsala University.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Jansson, Ulf
    Uppsala University.
    Electronic Structure and Chemical Bonding of AmorphousChromium Carbide Thin Films2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, p. 225004-Article in journal (Refereed)
    Abstract [en]

    The microstructure, electronic structure, and chemical bonding of chromium carbidethin films with different carbon contents have been investigated with high-resolutiontransmission electron microscopy, electron energy loss spectroscopy and soft x-rayabsorption-emission spectroscopies. Most of the films can be described as amorphousnanocomposites with non-crystalline CrCx in an amorphous carbon matrix. At highcarbon contents, graphene-like structures are formed in the amorphous carbon matrix.At 47 at% carbon content, randomly oriented nanocrystallites are formed creating acomplex microstructure of three components. The soft x-ray absorption-emissionstudy shows additional peak structures exhibiting non-octahedral coordination andbonding.

  • 37.
    Magnuson, Martin
    et al.
    Uppsala University.
    Butorin, Sergei
    Uppsala University.
    Agui, Akane
    Uppsala University.
    Nordgren, Joseph
    Uppsala University.
    Resonant soft x-ray Raman scattering of NiO2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 13, p. 3669-3676Article in journal (Refereed)
    Abstract [en]

    Resonant soft x-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d-d and charge-transfer excitations. The spectra are interpreted within the single-impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet-triplet and triplet-singlet transitions of the 3d8 configuration. For excitation energies corresponding to the charge-transfer region in the Ni 2p x-ray absorption spectrum of NiO, the emission spectra are instead dominated by charge-transfer transitions to the 3d9\underline L-1 final state. Comparisons of the final states with other spectroscopical techniques are also made.

  • 38.
    Magnuson, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Mattesini, Maurizio
    Departamento de F í sica de la Tierra, Astronom í a y Astrof í sica I, Universidad Complutense de Madrid, Madrid, Spain; Instituto de Geociencias (CSIC-UCM), Facultad de CC. F í sicas, Madrid, Spain.
    Bugnet, Mattieu
    Département de Physique et Mecanique des Matériaux, Institut Pprime, UPR 3346 CNRS: Université de Poitiers: ENSMA, SP2MI, Futuroscope, France; Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Département de Physique et Mecanique des Matériaux, Institut Pprime, UPR 3346 CNRS: Université de Poitiers: ENSMA, SP2MI, Futuroscope, France.
    The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft X-ray spectroscopy and ab initio calculations2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 41, p. 415501-415509Article in journal (Refereed)
    Abstract [en]

    The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal di erences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L2;3, C K, and Ge M1, M2;3 emission spectra are interpreted with rst-principles density-functional theory (DFT) including core-tovalence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should a ect the thermal expansion coecient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.

  • 39.
    Mattesini, Maurizio
    et al.
    Universidad Complutense de Madrid, Spain.
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Electronic correlation effects in the Cr2GeC Mn+1AXn phase2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 3, p. 035601-Article in journal (Refereed)
    Abstract [en]

    The magnetic properties, electronic band structure and Fermi surfaces of the hexagonal Cr2GeC system have been studied by means of both generalized gradient approximation (GGA) and the +U corrected method (GGA + U). The effective U value has been computed within the augmented plane wave theoretical scheme by following the constrained density functional theory formalism of Anisimov and Gunnarsson (1991 Phys. Rev. B 45 7570–74). On the basis of our GGA + U calculations, a compensated antiferromagnetic spin ordering of Cr atoms has been found to be the ground-state solution for this material, where a Ge-mediated super-exchange coupling is responsible for an opposite spin distribution between the ABA stacked in-plane Cr–C networks. Structural properties have also been tested and found to be in good agreement with the available experimental data. Topological analysis of Fermi surfaces has been used to qualitatively address the electronic transport properties of Cr2GeC, and found an important asymmetrical carrier-type distribution within the hexagonal crystal lattice. We conclude that an appropriate description of the strongly correlated Cr d electrons is an essential issue for interpreting the material properties of this unusual Cr-based MAX phase.

  • 40.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Bound excitons in GaN2001In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, no 32, p. 7011-7026Article in journal (Refereed)
    Abstract [en]

    The electronic structure of bound excitons in GaN is discussed, with reference to available optical data. Emphasis is given to the neutral-donor and neutralacceptor spectra, which are the most prominent ones in the experimental photoluminescence data. Two dominant donor bound excitons are observed with photoluminescence lines just above 3.47 eV at 2 K in unstrained samples, tentatively associated with Si and O shallow donors. Several acceptor bound excitons are present, the most prominent one with a photoluminescence line at about 3.466 eV is tentatively assigned to the Mg acceptor. We attempt an explanation of the available data from magneto-optical experiments on this line in terms of a spin-like acceptor hole, as observed in independent magnetic resonance data. Characteristic deep emissions related to P and As doping are reported, they may be interpreted in terms of isoelectronic bound excitons. Excitons bound to structural defects in GaN are also briefly discussed.

  • 41.
    Myneni, S.
    et al.
    Earth Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA, Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
    Luo, Y
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden, Theoretical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Näslund, L. Å.
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden.
    Cavalleri, M.
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden.
    Ojamäe, L.
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry .
    Ogasawara, H
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden, Permanent address: RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan..
    Pelmenschikov, A.
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden.
    Wernet, Ph.
    Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    Heske, C.
    Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA.
    Hussain, Z
    Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA.
    Pettersson, L. G. M.
    FYSIKUM, Stockholm University, Box 6730, S-113 85 Stockholm, Sweden.
    Nilsson, A.
    Department of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden, Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    Spectroscopic probing of local hydrogen-bonding structures in liquid water2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 8, p. L213-L219Article in journal (Refereed)
    Abstract [en]

    We have studied the electronic structure of liquid water using x-ray absorption spectroscopy at the oxygen K edge. Since the x-ray absorption process takes less than a femtosecond, it allows probing of the molecular orbital structure of frozen, local geometries of water molecules at a timescale that has not previously been accessible. Our results indicate that the electronic structure of liquid water is significantly different from that of the solid and gaseous forms, resulting in a pronounced pre-edge feature below the main absorption edge in the spectrum. Theoretical calculations of these spectra suggest that this feature originates from specific configurations of water, for which the H-bond is broken on the H-donating site of the water molecule. This study provides a fingerprint for identifying broken donating H-bonds in the liquid and shows that an unsaturated H-bonding environment exists for a dominating fraction of the water molecules.

  • 42.
    Nilsson, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Andersson, M.R.
    Department of Polymer Technology, Chalmers University of Technology, Göteborg, Sweden.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Conformational transitions of a free amino-acid-functionalized polythiophene induced by different buffer systems2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 42, p. 10011-10020Article in journal (Refereed)
    Abstract [en]

    A chiral, 3-substituted polythiophene with an amino-acid function shows pH-dependent visible, emission and circular dichroism spectra in buffered aqueous solution. At pH equal to the pI of the amino-acid, the backbone adopts a nonplanar right-handed helical conformation and the polymer chains are separated from each other. Increasing pH leads to a more planar conformation of the backbone and an aggregation of the polymer chains occurs. A lower pH will also lead to a more planar conformation of the backbone, but aggregation of the polymer chains appears to be absent. The aggregates are disrupted by increasing ionic strength in alkaline buffer systems, indicating hydrogen bonding is important for aggregation. On the other hand, ions containing an amino group and one or more hydroxyl groups induce a more planar conformation of the polymer backbone.

  • 43.
    Olovsson, Weine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Weinhardt, L
    University of Wurzburg, Germany.
    Fuchs, O
    University of Wurzburg, Germany.
    Tanaka, I
    Kyoto University, Japan.
    Puschnig, P
    University of Leoben, Austria.
    Umbach, E
    University of Wurzburg, Germany.
    Heske, C
    University of Wurzburg, Germany.
    Draxl, C
    University of Leoben, Austria.
    The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 31Article in journal (Refereed)
    Abstract [en]

    We have carried out a theoretical and experimental investigation of the beryllium K-edge soft x-ray absorption fine structure of beryllium compounds in the oxygen group, considering BeO, BeS, BeSe, and BeTe. Theoretical spectra are obtained ab initio, through many-body perturbation theory, by solving the Bethe–Salpeter equation (BSE), and by supercell calculations using the core-hole approximation. All calculations are performed with the full-potential linearized augmented plane-wave method. It is found that the two different theoretical approaches produce a similar fine structure, in good agreement with the experimental data. Using the BSE results, we interpret the spectra, distinguishing between bound core-excitons and higher energy excitations.

  • 44. Paulsson, M.
    et al.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Theoretical study of electron transport along self-assembled graphitic nanowires2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, no 45, p. 9433-9440Article in journal (Refereed)
    Abstract [en]

    Electron transport through stacks of polyaromatic hydrocarbons is studied theoretically using the Landauer formalism. The polyaromatic hydrocarbons can be synthesized in many different sizes and can form molecular stacks with a varying number of molecules and with a rather strong p-overlap along the stack. This allows for a large flexibility in the nanostructure of these materials and makes it possible to study the variation in the conductance with a number of different factors: a near-linear increase in the conductance as a function of the number of atoms in the individual molecule is observed. Furthermore, the conductance drops exponentially with the number of molecules in the stacks, from which it follows that an increase in the intermolecular hopping results in an increase in the conductance which is proportional to the intermolecular hopping to the power of 2(N-1), where N is the number of molecules in the stack.

  • 45. Pearton, SJ
    et al.
    Abernathy, CR
    Thaler, GT
    Frazier, RM
    Norton, DP
    Ren, F
    Park, YD
    Zavada, JM
    Buyanova, Irina A
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Hebard, AF
    Wide bandgap GaN-based semiconductors for spintronics2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 7, p. R209-R245Article, review/survey (Refereed)
    Abstract [en]

    Recent results on achieving ferromagnetism in transition-metal-doped GaN, A1N and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. There is strong potential for new classes of ultra-low-power, high speed memory, logic and photonic devices based on spintronics. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures and most theories predict that the Curie temperature will be a strong function of bandgap. We discuss the current state-of-the-art in producing room temperature ferromagnetism in GaN-based materials, the origins of the magnetism and its potential applications.

  • 46.
    Peng, Ru
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Wang, Y D
    Key Loaboratory for anisotropy and Texture of Materials Northeastern University, Shenyang.
    Nie, Z D
    Key Laboratory for Anisotropy and Texture of Materials Northeastern University, Shenyang.
    Oliver, E C
    ISIS Facility CCLRC rutherford Appleton Loaboratory Chilton, Didcot.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Liu, Y D
    Key Laboratory for Anisotropy and Texture of Materials Northeastern University, Shenyang.
    Ren, Y D
    X-ray Science Division Argonne National Laboratory, USA.
    Jorgensen, J D
    Intense Pulsed Neturon Source Argonne National Laboratory, USA.
    Fieramosca, J
    Intense Pulsed Neutron Source Argonne National Laboratory, USA.
    In situ neutron diffraction study of micromechanical interactions and phase transformation in Ni-Mn-Ga alloy under uniaxial and hydrostatic stress2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 10Article in journal (Refereed)
    Abstract [en]

    This paper deals with the experimental study of stress-induced phase transformation in a polycrystalline Ni-Mn-Ga alloy under uniaxial compression and its powder under hydrostatic compression. In situ neutron diffraction experiments were employed to follow changes in the structure and lattice strains caused by the applied stresses. Large lattice strains that are dependent on the lattice planes or grain orientations were observed in the parent Heusler phase for both the bulk material and the powder sample. The development of such anisotropic strains and the influence of external load conditions are discussed in the paper. © IOP Publishing Ltd.

  • 47.
    Raza, Zamaan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film 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; Tomsk State University, Russia.
    Computer simulations of glasses: the potential energy landscape2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 29, p. 293201-Article, review/survey (Refereed)
    Abstract [en]

    We review the current state of research on glasses, discussing the theoretical background and computational models employed to describe them. This article focuses on the use of the potential energy landscape (PEL) paradigm to account for the phenomenology of glassy systems, and the way in which it can be applied in simulations and the interpretation of their results. This article provides a broad overview of the rich phenomenology of glasses, followed by a summary of the theoretical frameworks developed to describe this phenomonology. We discuss the background of the PEL in detail, the onerous task of how to generate computer models of glasses, various methods of analysing numerical simulations, and the literature on the most commonly used model systems. Finally, we tackle the problem of how to distinguish a good glass former from a good crystal former from an analysis of the PEL. In summarising the state of the potential energy landscape picture, we develop the foundations for new theoretical methods that allow the ab initio prediction of the glass- forming ability of new materials by analysis of the PEL.

  • 48.
    Reeh, S
    et al.
    Rhein Westfal TH Aachen, Germany .
    Kasprzak, M
    Rhein Westfal TH Aachen, Germany .
    Klusmann, C D.
    Rhein Westfal TH Aachen, Germany .
    Stalf, F
    Rhein Westfal TH Aachen, Germany .
    Music, D
    Rhein Westfal TH Aachen, Germany .
    Ekholm, Marcus
    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.
    Schneider, J M.
    Rhein Westfal TH Aachen, Germany .
    Elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys studied by the combinatorial thin film approach and ab initio calculations2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 24Article in journal (Refereed)
    Abstract [en]

    The elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys with additions of up to 8 at.% X were studied by combinatorial thin film growth and characterization and by ab initio calculations using the disordered local moments (DLM) approach. The lattice parameter and Youngs modulus values change only marginally with X. The calculations and experiments are in good agreement. We demonstrate that the elastic properties of transition metal alloyed Fe-Mn can be predicted by the DLM model.

  • 49.
    Rosen, Johanna
    et al.
    Rhein Westfal TH Aachen.
    Larsson, K
    University of Uppsala.
    Schneider, JM
    Rhein Westfal TH Aachen.
    Ab initio molecular dynamics study of hydrogen removal by ion-surface interactions2005In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, no 15, p. L137-L142Article in journal (Refereed)
    Abstract [en]

    The energy dependence of surface reactions has been investigated through ab initio MD simulations for collisions between Al1+ and a gibbsite surface. No change in surface composition was observed for 0 eV initial kinetic energy of Al1+. An increase in energy to 3.5 eV resulted in extended surface migration of hydrogen, subsequent H-2 formation and desorption from the surface. These results may be understood based on thermodynamics and an increase in entropy upon H-2 formation. They are of fundamental importance for an increased understanding of thin film growth through the correlation between ion energy and film composition. They may also indicate a pathway to affect impurity incorporation during film growth.

  • 50. Sastry, M.D.
    et al.
    Gustafsson, Håkan
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Health Sciences, Radiation Physics .
    Danilczuk, M.
    Lund, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics .
    Dynamical effects and ergodicity in the dipolar glass phase: Evidence from time-domain EPR and phase memory time studies of AsO44- in Rb1-x(NH4)xH2PO4 (x = 0,0.5,1)2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 17, p. 4265-4284Article in journal (Refereed)
    Abstract [en]

    Three-pulse electron spin echo envelope modulation (ESEEM), hyperfine sublevel correlation spectroscopy (HYSCORE) investigations and two-pulse electron spin echo (ESE) measurements of phase memory time TM, were carried out, in the 20-200 K temperature range, on an AsO44- paramagnetic probe stabilized in RbH2PO4 (RDP), NH4H2PO4 (ADP), and dipolar glass Rb0.5(NH4)0.5H2PO4 (RADP). The results obtained on ADP revealed hyperfine interaction of the probe ion with the 14N of the ammonium ion, the coupling constant satisfying the condition of 'cancellation' at a field of 480 mT. The ammonium ion was found to be in two different sites in ADP, which became indistinguishable on the formation of dipolar glass RADP. These results were confirmed by HYSCORE spectral measurements. The fast Fourier transform (FFT) spectra of three-pulse ESEEM decays have clearly revealed the interaction with protons in the bond both in ADP and RDP, and in RADP with an averaged coupling constant. The phase memory times in RADP exhibited strong temperature dependence and were found to be dependent on the nuclear spin quantum number mI of 75As. The temperature dependence of TM exhibited a well-defined maximum around 90 K, coinciding with the temperature of onset of 'freezing' in Rb0.5(NH4)0.5H2PO 4. This is symptomatic of dynamic fluctuations in the dipolar glass phase, with onset around 150 K, going through a maximum around 90 K and slowing down on further cooling. These results suggest that in RADP, a dynamical mechanism with progressive slowing down below 90 K is operative in the glass formation. This implies that the RADP system, with x = 0.5, exists in an ergodic relaxor (R)-state in the 20-200 K temperature range wherein every fluctuating monodomain can be viewed as statistically representative of the whole sample. © IOP Publishing Ltd.

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