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  • 1.
    Abergel, David S. L.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Center for Quantum Materials, Sweden.
    Robustness of topologically protected transport in graphene-boron nitride lateral heterostructures2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 7, article id 075303Article in journal (Refereed)
    Abstract [en]

    Previously, graphene nanoribbons set in lateral heterostructures with hexagonal boron nitride were predicted to support topologically protected states at low energy. We investigate how robust the transport properties of these states are against lattice disorder. We find that forms of disorder that do not couple the two valleys of the zigzag graphene nanoribbon do not impact the transport properties at low bias, indicating that these lateral heterostructures are very promising candidates for chip-scale conducting interconnects. Forms of disorder that do couple the two valleys, such as vacancies in the graphene ribbon, or substantial inclusions of armchair edges at the graphene-hexagonal boron nitride interface will negatively affect the transport. However, these forms of disorder are not commonly seen in current experiments.

  • 2.
    Abergel, David S. L.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Robustness of topologically protected transport in graphene-boron nitride lateral heterostructures2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 7, article id 075303Article in journal (Refereed)
    Abstract [en]

    Previously, graphene nanoribbons set in lateral heterostructures with hexagonal boron nitride were predicted to support topologically protected states at low energy. We investigate how robust the transport properties of these states are against lattice disorder. We find that forms of disorder that do not couple the two valleys of the zigzag graphene nanoribbon do not impact the transport properties at low bias, indicating that these lateral heterostructures are very promising candidates for chip-scale conducting interconnects. Forms of disorder that do couple the two valleys, such as vacancies in the graphene ribbon, or substantial inclusions of armchair edges at the graphene-hexagonal boron nitride interface will negatively affect the transport. However, these forms of disorder are not commonly seen in current experiments.

  • 3.
    Adell, J.
    et al.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Ulfat, I.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden / Department of Physics, University of Karachi, Karachi, Pakistan.
    Ilver, L.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Sadowski, J.
    Institute of Physics, Polish Academy of Sciences, Warsaw, Poland / MAX-lab, Lund University, Lund, Sweden.
    Karlsson, Krister
    University of Skövde, School of Life Sciences.
    Kanski, J.
    Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 8, article id 085003Article in journal (Refereed)
    Abstract [en]

    Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.

  • 4.
    Adlmann, Franz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Herbel, Jörg
    ETH Zürich, Zürich, Switzerland.
    Korolkovas, Airidas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Bliersbach, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Toperverg, Boris
    Petersburg Nuclear Physics Institute, Gatchina, Russia.
    Van Herck, Walter
    Forschungszentrum Jülich GmbH, Garching, Germany.
    Pálsson, Gunnar K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Kitchen, Brian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, article id 165901Article in journal (Refereed)
    Abstract [en]

    Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.

  • 5.
    Ahuja, Rajeev
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Osorio-Guillen, J. M.
    de Almeida, J. S.
    Holm, B.
    Ching, W. Y.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Electronic and optical properties of gamma-Al2O3 from ab initio theory2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 16, p. 2891-2900Article in journal (Refereed)
    Abstract [en]

    We report on a density functional theory calculation of the electronic structure and optical properties of gamma-Al2O3. We have made a comparison between the optical and electronic properties of the alpha and gamma phases of alumina. The calculated bulk modulus of the gamma phase is slightly lower than that of the a phase. The calculated static dielectric function and the optical constant of the gamma phase are very close to those of the alpha phase.

  • 6.
    Alekhin, A.
    et al.
    CNRS, Inst Mol & Mat Le Mans, UMR 6283, F-72085 Le Mans, France.
    Razdolski, I.
    CNRS, Inst Mol & Mat Le Mans, UMR 6283, F-72085 Le Mans, France;Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany.
    Berritta, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Buerstel, D.
    Univ Duisburg Essen, Fac Chem, Univ Str 5, D-45141 Essen, Germany.
    Temnov, V.
    CNRS, Inst Mol & Mat Le Mans, UMR 6283, F-72085 Le Mans, France.
    Diesing, D.
    Univ Duisburg Essen, Fac Chem, Univ Str 5, D-45141 Essen, Germany.
    Bovensiepen, U.
    Univ Duisburg Essen, Fac Phys, Lotharstr 1, D-47057 Duisburg, Germany;Univ Duisburg Essen, Ctr Nanointegrat CENIDE, Lotharstr 1, D-47057 Duisburg, Germany.
    Woltersdorf, G.
    Martin Luther Univ Halle Wittenberg, Inst Phys, Von Danckelmann Pl 3, D-06120 Halle, Germany.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Melnikov, A.
    Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany;Martin Luther Univ Halle Wittenberg, Inst Phys, Von Danckelmann Pl 3, D-06120 Halle, Germany.
    Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 12, article id 124002Article in journal (Refereed)
    Abstract [en]

    We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm fs(-1) (close to the Fermi velocity) and the decay length on the order of 100nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.

  • 7.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lebègue, Sébastien
    Laboratoire de Cristallographie, Résonance Magnétique et Modélisations, Institut Jean Barriol, Nancy Université, Vandoeuvre-lès-Nancy, France.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adsorption of Cu, Ag, and Au atoms on graphene including van der Waals interactions2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 39, article id 395001Article in journal (Refereed)
    Abstract [en]

    We performed a systematic density functional (DF) study of the adsorption of copper, silver, and gold adatoms on pristine graphene, especially accounting for van der Waals (vdW) interactions by the vdW-DF and PBE + D2 methods. In particular, we analyze the preferred adsorption site (among top, bridge, and hollow positions) together with the corresponding distortion of the graphene sheet and identify diffusion paths. Both vdW schemes show that the coinage metal atoms do bind to the graphene sheet and that in some cases the buckling of the graphene layer can be significant. Only the results for silver are qualitatively at variance with those obtained with the generalized gradient approximation, which gives no binding in this case. However in all three cases, we observe some quantitative differences between the vdW-DF and PBE + D2 methods. For instance the adsorption energies calculated with the PBE + D2 method are systematically higher than the ones obtained with vdW-DF. Moreover, the equilibrium distances computed with PBE + D2 are shorter than those calculated with the vdW-DF method.

  • 8.
    Amft, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Calculated magneto-optical Kerr spectra of the half-Heusler compounds AuMnX (X = In, Sn, Sb)2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 31, p. 315216-Article in journal (Refereed)
    Abstract [en]

    The ferromagnetic ground states of the half-Heusler compounds AuMnX (X ≤ In, Sn, Sb) have been calculated in the framework of the local spin-density approximation (LSDA) to density functional theory (DFT). AuMnSn is computed to be a half-metallic ferromagnet, whereas AuMnIn and AuMnSb are not half-metallic, due to their different band filling. The computed relativistic electronic structures served as inputs to calculate the magneto-optical Kerr rotations and ellipticities for all three materials. In the case of AuMnSn the largest, zero-temperature, polar Kerr rotation has been found to be -0.45° at about 1eV photon energy. The computed MOKE spectra of AuMnSn are in qualitative agreement with recent experiments. The largest Kerr rotations of AuMnIn and AuMnSb have been calculated to be +0.64° at 4.3eV and -0.85° at 0.9eV, respectively.

  • 9.
    Andersson, Gabriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Björck, Matts
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Lidbaum, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Chacon, Cyril
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Zlotea, Claudia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Valizadeh, Sima
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Structure of Fe-Co/Pt(001) superlattices: a realization of tetragonal Fe-Co alloys2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 1, p. 016008-Article in journal (Refereed)
    Abstract [en]

    The structural properties of a tetragonally distorted Fe1-xCox alloy, in the form of Fe1-xCox/Pt(001) superlattices with x = 0.64, have been investigated experimentally. The study follows recent theoretical predictions on the enhanced uniaxial magnetocrystalline anisotropy of such alloys with specific combinations of chemical composition and tetragonal distortion. The ratio between out-of-plane and in-plane lattice parameters in the Fe0.36Co0.64 layers, c/a, was found to vary between 1.18 and 1.31, depending on the thickness ratio between the alloy and the spacer. This covered the range of interest c/a = 1.20-1.25 in the previous calculations and should be compared to c/a = 1 in the original bcc alloy lattice. Simulations of x-ray diffraction patterns as well as density functional calculations support the derivation of the Fe0.36Co0.64 lattice parameters.

  • 10.
    Andersson, Garbriella
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Andersson, Per H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Höjvarsson, B.
    Effects of varying compressive biaxial strain on the hydrogen uptake of thin vanadium (001) layers1999In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 11, no 35, p. 6669-6677Article in journal (Refereed)
    Abstract [en]

    The hydrogen uptake of asymmetric Fe/V (001) superlattices with LFe/LV = 3/16 monolayers and 3/10 monolayers was investigated by resistometric methods. The hydrogen distribution and the enthalpy of solution were simulated using a diffusion model and calculated H-H interaction energies. It was found that the strain state of the V lattice strongly influenced the H-H interaction. The hydrogen-depleted interface region in the V layers was populated at lower concentrations than in previously studied symmetric samples, which implied that the energy difference between interior and interface regions was lowered. The V-H binding energy was found to be up to 60 meV higher than in the symmetric superlattices.

  • 11. Araujo, C. M.
    et al.
    Blomqvist, A.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ti-induced destabilization of NaBH4 from first-principles theory2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 12Article in journal (Refereed)
    Abstract [en]

    In this work, we have employed first-principles total energy calculations and ab initio molecular dynamics simulations to investigate the Ti doping of NaBH4. We show that Ti destabilizes the BH4 cages, which in turn increases the mobility of hydrogen atoms. Such an effect is shown to be due to the formation of B-Ti bonds, rather than the lowering of the BH4 charge state as expected. These results indicate that Ti may catalyse the dehydrogenation process in NaBH4 as it does for NaAlH4.

  • 12.
    Araújo, C. Moysés
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ti-induced destabilization of NaBH4 from first-principles theory2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 12, p. 122202-Article in journal (Refereed)
    Abstract [en]

    In this work, we have employed first-principles total energy calculations and ab initio molecular dynamics simulations to investigate the Ti doping of NaBH4. We show that Ti destabilizes the BH4 cages, which in turn increases the mobility of hydrogen atoms. Such an effect is shown to be due to the formation of B-Ti bonds, rather than the lowering of the BH4 charge state as expected. These results indicate that Ti may catalyse the dehydrogenation process in NaBH4 as it does for NaAlH4.

  • 13.
    Atumi, M.K.
    et al.
    Newcastle University.
    Goss, J.P.
    Newcastle University.
    Briddon, P.R.
    Newcastle University.
    Shirf, F.E.
    Newcastle University.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Hyperfine interactions at nitrogen interstitial defects in diamond2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 6Article in journal (Refereed)
    Abstract [en]

    Diamond has many extreme physical properties and it can be used in a wide range of applications. In particular it is a highly effective particle detection material, where radiation damage is an important consideration. The WAR9 and WAR10 are electron paramagnetic resonance centres seen in irradiated, nitrogen-containing diamond. These S = 1/2 defects have C2v and C1h symmetry, respectively, and the experimental spectra have been interpreted as arising from nitrogen split-interstitial centres. Based upon the experimental and theoretical understanding of interstitial nitrogen defect structures, the AIMPRO density functional code has been used to assess the assignments for the structures of WAR9 and WAR10. Although the calculated hyperfine interaction tensors are consistent with the measured values for WAR9, the thermal stability renders the assignment problematic. The model for the WAR10 centre yields principal directions of the hyperfine tensor at variance with observation. Alternative models for both centres are discussed in this paper, but no convincing structures have been found.

  • 14.
    Autieri, Carmine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Antiferromagnetic and xy ferro-orbital order in insulating SrRuO3 thin films with SrO termination2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 42, article id 426004Article in journal (Refereed)
    Abstract [en]

    By means of first-principles calculations we study the structural, magnetic and electronic properties of SrRuO3 surface for the SrO termination. We find that the RuO6 octahedra and the structure of the SrO layers at the surface are strongly modified as well as the Ru-O-Ru bond angles. We find in the thin films a d(xy) ferro-orbital order. The d(xy) orbital becomes the lowest in energy as in other quasitwodimensional ruthenates. Such structural rearrangement, together with a band reduction, leads to a modification of the magnetic properties. We compare the Jahn-Teller effect between the ferromagnetic and antiferromagnetic phases. We show that an insulating G-type antiferromagnetic phase takes place in SrRuO3 thin films, substituting the metallic phase experimentally found in every bulk Sr-ruthenates. The single layer SrRuO3 presents many similarities with the Ca2RuO4 low temperature phase, these similarities disappear with a larger number of layers. A study of the ground state of the as function of the number of layers is presented, the competition between bandwidth and Coulomb repulsion determines the ground state. We propose the disorder as responsible for the exchange bias effect observed.

  • 15.
    Autieri, Carmine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A systematic study of 4d and 5d transition metal mediated exchange coupling between Fe and Gd nanolaminates2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 46, article id 465802Article in journal (Refereed)
    Abstract [en]

    We present a systematic study of the magnetic coupling between iron and gadolinium layers intermediated by 4d and 5d transition metals using density functional theory. We demonstrate that it is possible to find a magnetic coupling for most of them. In particular, for the early transition metals (d(1), d(2), d(3) and d(4)), a ferromagnetic coupling occurs even stronger than the 3d interlayers. Atomic size and the electronic configuration of the transition metals are crucial for the nature of the coupling. All the open shell transition metals present induced magnetic moments. By increasing the number of interlayers, an oscillating behavior in the magnetic coupling was found and the magnetic coupling goes to zero beyond four spacer layers. Using Monte Carlo simulations, we demonstrate that the interlayer strongly enhances the critical temperature in the Gd layers closest to the interface.

  • 16.
    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.

  • 17.
    Balaz, Pavel
    et al.
    Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu 5, CZ-12116 Prague, Czech Republic..
    Zonda, Martin
    Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu 5, CZ-12116 Prague, Czech Republic..
    Carva, Karel
    Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu 5, CZ-12116 Prague, Czech Republic..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Transport theory for femtosecond laser-induced spin-transfer torques2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 11, article id 115801Article in journal (Refereed)
    Abstract [en]

    Ultrafast demagnetization of magnetic layers pumped by a femtosecond laser pulse is accompanied by a nonthermal spin-polarized current of hot electrons. These spin currents are studied here theoretically in a spin valve with noncollinear magnetizations. To this end, we introduce an extended model of superdiffusive spin transport that enables the treatment of noncollinear magnetic configurations, and apply it to the perpendicular spin valve geometry. We show how spin-transfer torques arise due to this mechanism and calculate their action on the magnetization present, as well as how the latter depends on the thicknesses of the layers and other transport parameters. We demonstrate that there exists a certain optimum thickness of the out-of-plane magnetized spin-current polarizer such that the torque acting on the second magnetic layer is maximal. Moreover, we study the magnetization dynamics excited by the superdiffusive spin-transfer torque due to the flow of hot electrons employing the Landau-Lifshitz-Gilbert equation. Thereby we show that a femtosecond laser pulse applied to one magnetic layer can excite small-angle precessions of the magnetization in the second magnetic layer. We compare our calculations with recent experimental results.

  • 18. Banerjee, Rudra
    et al.
    Banerjee, Mitali
    Majumdar, A. K.
    Mookerjee, Abhijit
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nigam, A. K.
    Fe3.3Ni83.2Mo13.5: a likely candidate to show spin-glass behaviour at low temperatures2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 10, p. 106002-Article in journal (Refereed)
    Abstract [en]

    Unlike other transition metals alloyed with a non-magnetic metal, alloys of Ni behave rather differently. This is because of the fragility of the local magnetic moment on Ni. NiMo and NiW do not show any spin-glass phase. However, addition of Fe can bolster the moment on Ni. We wish to study whether the alloy Fe3.3Ni83.2Mo13.5, chosen near a composition where mean-field estimates suggest there could be a spin-glass phase, shows such a phase or not.

  • 19. Belabbes, A.
    et al.
    Zaoui, A.
    Ferhat, Marhoun
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Lattice mismatch consequences for the intrinsic characteristics in the dilute (Zn, Se)O alloys2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 45, p. 456212-Article in journal (Refereed)
    Abstract [en]

    By means of ab initio pseudopotential calculations, we investigate the effect of lattice mismatch on the intrinsic properties in the dilute ZnOxSe1- x alloys. The substitution of isovalent elements having a large electronegativity and size mismatch with respect to the replaced atoms leads to strong nonlinear effects in the properties of the host crystal. From a detailed analysis of the bowing, we notice that the relative contribution of the three components ( volume, charge exchange, and strain) shows that the most significant effect is caused by the structural relaxation.

  • 20. Belhadji, Brahim
    et al.
    Bergqvist, Lars
    Institut fuer Festkoerperforschung, Forschungszentrum Juelich.
    Zeller, Rudi
    Dederichs, Peter H.
    Sato, Kazunori
    Katayama-Yoshida, H
    Trends of exchange interactions in dilute magnetic semiconductors2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 43, p. 436227-Article in journal (Refereed)
    Abstract [en]

    We discuss the importance of different exchange mechanisms like double exchange, p–d exchange and anti-ferromagnetic as well as ferromagnetic superexchange in dilute magnetic semiconductors (DMSs). Based on the coherent potential approximation for the electronic structure of the DMSs we show that the different mechanisms exhibit different dependences on the concentration of the magnetic impurities, on the hybridization with the wavefunctions of neighbouring impurities and on the position of the Fermi level in the band gap. However, common to all mechanisms is that, as long as half-metallicity is preserved, they are determined by the hybridization with the orbitals of neighbouring impurities and of the resulting energy gain due to the formation of bonding and anti-bonding hybrids. By calculating the exchange coupling constants Jij(EF) as a function of the position of the Fermi level we obtain a universal trend for the exchange interactions with band filling.

  • 21. Belonoshko, A. B.
    et al.
    Arapan, Sergiu
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rosengren, A.
    An ab initio molecular dynamics study of iron phases at high pressure and temperature2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 48, p. 485402-Article in journal (Refereed)
    Abstract [en]

    The crystal structure of iron, the major component of the Earth's inner core (IC), is unknown for the IC high pressure (P; 3.3-3.6 Mbar) and temperature (T; 5000-7000 K). There is mounting evidence that the hexagonal close-packed (hcp) phase of iron, stable at the high P of the IC and a low T, might be unstable under the IC conditions due to the impact of high T and impurities. Experiments at the IC P and T are difficult and do not provide a conclusive answer as regards the iron stability at the pressure of the IC and temperatures close to the iron melting curve. Recent theory provides contradictory results regarding the nature of the stable Fe phase. We investigated the possibility of body-centered cubic (bcc) phase stabilization at the P and T in the vicinity of the Fe melting curve by using ab initio molecular dynamics. Thermodynamic calculations, relying on the model of uncorrelated harmonic oscillators, provide nearly identical free energies within the error bars of our calculations. However, direct simulation of iron crystallization demonstrates that liquid iron freezes in the bcc structure at the P of the IC and T = 6000 K. All attempts to grow the hcp phase from the liquid failed. The mechanism of bcc stabilization is explained. This resolves most of the earlier confusion.

  • 22.
    Belonoshko, Anatoly
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Arapan, S.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    An ab initio molecular dynamics study of iron phases at high pressure and temperature2011In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 48Article in journal (Refereed)
    Abstract [en]

    The crystal structure of iron, the major component of the Earth's inner core (IC), is unknown for the IC high pressure (P; 3.3-3.6 Mbar) and temperature (T; 5000-7000 K). There is mounting evidence that the hexagonal close-packed (hcp) phase of iron, stable at the high P of the IC and a low T, might be unstable under the IC conditions due to the impact of high T and impurities. Experiments at the IC P and T are difficult and do not provide a conclusive answer as regards the iron stability at the pressure of the IC and temperatures close to the iron melting curve. Recent theory provides contradictory results regarding the nature of the stable Fe phase. We investigated the possibility of body-centered cubic (bcc) phase stabilization at the P and T in the vicinity of the Fe melting curve by using ab initio molecular dynamics. Thermodynamic calculations, relying on the model of uncorrelated harmonic oscillators, provide nearly identical free energies within the error bars of our calculations. However, direct simulation of iron crystallization demonstrates that liquid iron freezes in the bcc structure at the P of the IC and T = 6000 K. All attempts to grow the hcp phase from the liquid failed. The mechanism of bcc stabilization is explained. This resolves most of the earlier confusion.

  • 23.
    Bergersen, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V.
    Marinho, R. R. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Pokapanich, Wandared
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sæthre, L. J.
    Department of Chemistry, University of Bergen.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V.
    Öhrwall, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics V.
    A photoelectron spectroscopic study of aqueous tetrabutylammonium iodide2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 32, p. 326101-Article in journal (Refereed)
    Abstract [en]

    Photoelectron spectra of tetrabutylammonium iodide (TBAI) dissolved in water have been recorded using a novel experimental set-up, which enables photoelectron spectroscopy of volatile liquids. The set-up is described in detail. Ionization energies are reported for I 5p, I 4d, C 1s and N 1s. The C 1s spectrum shows evidence of inelastic scattering of the photoelectrons, that differs from the case of TBAI in formamide.

  • 24.
    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.

  • 25.
    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.

  • 26.
    Bergman, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Klautau, Angela B.
    Frota-Pessôa, Sonia
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    A first-principles study of the magnetism and electronic structure of Cr clusters supported on a Au(111) surface2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 15, p. 156226-Article in journal (Refereed)
    Abstract [en]

    We have studied clusters of Cr on a Au(111) surface by means of a first-principles method that allows for non-collinear magnetic ordering. We find that the Cr atoms possess a large magnetic moment, of order 4 μB/atom, and have essentially antiferromagnetic interatomic exchange interactions. This leads to collinear magnetic arrangements in linear clusters (dimers and trimers) and non-collinear ordering in clusters where antiferromagnetism becomes frustrated, such as in triangular geometries.

  • 27.
    Bergqvist, Lars
    et al.
    Institut für Festkörperforschung, Forschungszentrum Jülich.
    Dederichs, Peter H.
    A theoretical study of half-metallic antiferromagnetic diluted magnetic semiconductors2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 21, p. 216220-Article in journal (Refereed)
    Abstract [en]

    Based on electronic structure calculations and statistical methods, we investigate a new class of materials for spintronic applications: half-metallic antiferromagnetic diluted magnetic semiconductors (HMAF-DMSs). As shown recently by Akai and Ogura, these DMS systems contain equal amounts of low-valent and high-valent transition metal impurities, such that their local moments exactly compensate each other. We present ab initio calculations using the KKR-CPA and the PAW-supercell methods, and show that quite a few half-metallic antiferromagnets should exist. Our calculations demonstrate that the exchange coupling parameters in these systems are dominated by a strong antiferromagnetic interaction between the two impurities. The Néel temperatures are calculated by Monte Carlo simulations and in mean-field approximation. It is shown that the latter method strongly overestimates the critical temperatures and that the more realistic values obtained by Monte Carlo techniques are rather low.

  • 28.
    Bergqvist, Lars
    et al.
    Uppsala University.
    Eriksson, Olle
    Theory of weakly coupled two-dimensional magnets2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 20, p. 4853-4860Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the experimental findings of the magnetic properties of the weakly coupled trilayer system Ni4/CuN/Co2are reproduced by a theory that combines first principles calculations of the exchange interactions in a classical Heisenberg model with Monte Carlo simulations. Through an analysis of the spin–spin correlation function we show that two distinct temperatures can be identified; a higher temperature where long range magnetic order disappears and a lower temperature where the spin–spin correlation of the Ni atoms undergoes a drastic change. We argue that our findings hold in general for 'weak exchange link' systems.

  • 29.
    Bergqvist, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Theoretical Magnetism.
    Theory of weakly coupled two-dimensional magnets2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 20, p. 4853-Article in journal (Refereed)
    Abstract [en]

    We demonstrate that the experimental findings of the magnetic properties of the weakly coupled trilayer system Ni4/CuN/Co2are reproduced by a theory that combines first principles calculations of the exchange interactions in a classical Heisenberg model with Monte Carlo simulations. Through an analysis of the spin–spin correlation function we show that two distinct temperatures can be identified; a higher temperature where long range magnetic order disappears and a lower temperature where the spin–spin correlation of the Ni atoms undergoes a drastic change. We argue that our findings hold in general for 'weak exchange link' systems.

  • 30.
    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.

  • 31.
    Bhattacharjee, Satadeep
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    First principles calculations of magnetism, dielectric properties and spin-phonon coupling in double perovskite Bi2CoMnO62012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 29, p. 295901-Article in journal (Refereed)
    Abstract [en]

    First principles electronic structure calculations have been performed for the double perovskite Bi2CoMnO6 in its non-centrosymmetric polar state using the generalized gradient approximation plus the Hubbard U approach. We find that the ferromagnetic state is more favored compared to the ferrimagnetic state with both Co and Mn in high spin states. The calculated dynamical charge tensors are anisotropic reflecting a low-symmetry structure of the compound. The magnetic structure dependent phonon frequencies indicate the presence of a weak spin-phonon coupling. Using the Berry phase method, we obtain a spontaneous ferroelectric polarization of 5.88 mu C cm(-2), which is close to the experimental value observed for a similar compound, Bi2NiMnO6.

  • 32.
    Björck, M
    et al.
    Paul Scherrer Institut.
    Schlepütz, C M
    Paul Scherrer Institut.
    Pauli, S A
    Paul Scherrer Institut.
    Martoccia, D
    Paul Scherrer Institut.
    Herger, R
    Paul Scherrer Institut.
    Willmott, P R
    Paul Scherrer Institut.
    Atomic imaging of thin films with surface x-ray diffraction: introducing DCAF2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20Article in journal (Refereed)
  • 33.
    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.

  • 34.
    Björström, Cecilia M.
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Bernasik, Andrzej
    Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Kraków, Poland.
    Rysz, Jakub
    Institute of Physics, Jagiellonian University, Kraków, Poland.
    Budkowski, Andrzej
    Institute of Physics, Jagiellonian University, Kraków, Poland.
    Nilsson, Svante
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Svensson, Mattias
    Department of Materials and Surface Chemistry/Polymer Technology, Chalmers University of Technology, Göteborg.
    Andersson, Mats R.
    Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Magnusson, Kjell
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Multilayer formation in spin-coated thin films of low-bandgap polyfluorene:PCBM blends2005In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, no 50, p. L529-L534Article in journal (Refereed)
    Abstract [en]

    Blends of the low-bandgap polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5- (4',7'-di-2-thienyl-2',1',3'-benzothiadiazole] (APFO-3) and the fullerene derivative [6,6]-phenyl–C61–butyric acid methyl ester (PCBM) were spin-coated from chloroform solution into thin films, which were examined with dynamic secondary ion mass spectrometry. For blends with high PCBM content, the depth profiles show composition waves that were caused by surface-directed phase separation during spin-coating. The formation of such multilayer structures by spontaneous self-stratification is likely to have implications for optimization strategies for the performance of organic solar cells

  • 35.
    Black-Schaffer, Annica M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Honerkamp, Carsten
    Chiral d-wave superconductivity in doped graphene2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 42, p. 423201-Article, review/survey (Refereed)
    Abstract [en]

    A highly unconventional superconducting state with a spin-singlet d(x2-y2) +/- id(xy)-wave, or chiral d-wave symmetry has recently been suggested to emerge from electron-electron interactions in doped graphene. It has been argued that graphene doped to the van Hove singularity at 1/4 doping, where the density of states diverge, is particularly likely to be a chiral d-wave superconductor. In this review we summarize the currently mounting theoretical evidence for the existence of a chiral d-wave superconducting state in graphene, obtained with methods ranging from mean-field studies of effective Hamiltonians to angle-resolved renormalization group calculations. We further discuss the multiple distinctive properties of the chiral d-wave superconducting state in graphene, as well as its stability in the presence of disorder. We also review the means of enhancing the chiral d-wave state using proximity-induced superconductivity. The appearance of chiral d-wave superconductivity is intimately linked to the hexagonal crystal lattice and we also offer a brief overview of other materials which have also been proposed to be chiral d-wave superconductors.

  • 36.
    Blumenau, A.T.
    et al.
    University of Exeter.
    Elsner, J.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Heggie, M.I.
    University of Sussex.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Frauenheim, T.
    Universität Paderborn.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Dislocations in hexagonal and cubic GaN2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, p. 10223-10233Article in journal (Refereed)
    Abstract [en]

    The structure and electronic activity of several types of dislocations in both hexagonal and cubic GaN are calculated using first-principles methods. Most of the stoichiometric dislocations investigated in hexagonal GaN do not induce deep acceptor states and thus cannot be responsible for the yellow luminescence. However, it is shown that electrically active point defects, in particular gallium vacancies and oxygen-related defect complexes, can be trapped at the stress field of the dislocations and may be responsible for this luminescence. For cubic GaN, we find the ideal stoichiometric 60° dislocation to be electrically active and the glide set to be more stable than the shuffle. The dissociation of the latter is considered

  • 37.
    Blumenau, A.T.
    et al.
    Theoretische Physik, Universität Paderborn.
    Fall, C.J.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Theoretische Physik, Universität Paderborn.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Straight and kinked 90° partial dislocations in diamond and 3C-SiC2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 48, p. 12741-12747Article in journal (Refereed)
    Abstract [en]

    Density-functional based calculations are used to investigate low energy core structures of 90° partial dislocations in diamond and 3C-SiC. In both materials dislocation glide is analysed in terms of kink formation and migration and the fundamental steps to kink migration are investigated. We find the C terminated core structure in SiC to be more mobile than the Si core. However, the Si partial is electrically active and this opens the possibility of recombination-enhanced glide under ionizing conditions or an enhanced mobility in doped material.

  • 38.
    Blumenau, A.T.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Frauenheim, T.
    Universität Paderborn.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Optical bands related to dislocations in Si2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, p. 10123-10129Article in journal (Refereed)
    Abstract [en]

    First-principles calculations are used to investigate the interaction of self-interstitial aggregates with the 90° partial dislocation in Si. We find that I4 is bound to the line with an energy of around 3 eV. The defect causes deep levels to appear in the band gap and optical transitions between these levels may account for the luminescent bands relating to plastically deformed Si.

  • 39.
    Bondarenko, N.
    et al.
    Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, S-75121 Uppsala, Sweden. riksson, O..
    Eriksson, O.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, S-75121 Uppsala, Sweden.
    Pereiro, M.
    Multi-polaron solutions, nonlocal effects and internal modes in a nonlinear chain2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 41, article id 415401Article in journal (Refereed)
    Abstract [en]

    Multipolaron solutions were studied in the framework of the Holstein one-dimensional molecular crystal model. The study was performed in the continuous limit where the crystal model maps into the nonlinear Schrodinger equation for which a new periodic dnoidal solution was found for the multipolaron system. In addition, the stability of the multi-polaron solutions was examined, and it was found that dnoidal and dnoidal solutions stabilize in different ranges of the parameter space. Moreover, the model was studied under the influence of nonlocal effects and the polaronic dynamics was described in terms of internal solitonic modes.

  • 40.
    Bondarenko, N.
    et al.
    Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Skorodumova, N. , V
    Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Multiscale Materials Modelling, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Pereiro, M.
    Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Multi-polaron solutions, nonlocal effects and internal modes in a nonlinear chain2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 41, article id 415401Article in journal (Refereed)
    Abstract [en]

    Multipolaron solutions were studied in the framework of the Holstein one-dimensional molecular crystal model. The study was performed in the continuous limit where the crystal model maps into the nonlinear Schrodinger equation for which a new periodic dnoidal solution was found for the multipolaron system. In addition, the stability of the multi-polaron solutions was examined, and it was found that dnoidal and dnoidal solutions stabilize in different ranges of the parameter space. Moreover, the model was studied under the influence of nonlocal effects and the polaronic dynamics was described in terms of internal solitonic modes.

  • 41.
    Bonetti, Stefano
    Stockholm University, Faculty of Science, Department of Physics.
    X-ray imaging of spin currents and magnetisation dynamics at the nanoscale2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 13, article id 133004Article in journal (Refereed)
    Abstract [en]

    Understanding how spins move in time and space is the aim of both fundamental and applied research in modern magnetism. Over the past three decades, research in this field has led to technological advances that have had a major impact on our society, while improving the understanding of the fundamentals of spin physics. However, important questions still remain unanswered, because it is experimentally challenging to directly observe spins and their motion with a combined high spatial and temporal resolution. In this article, we present an overview of the recent advances in x-ray microscopy that allow researchers to directly watch spins move in time and space at the microscopically relevant scales. We discuss scanning x-ray transmission microscopy (STXM) at resonant soft x-ray edges, which is available at most modern synchrotron light sources. This technique measures magnetic contrast through the x-ray magnetic circular dichroism (XMCD) effect at the resonant absorption edges, while focusing the x-ray radiation at the nanometre scale, and using the intrinsic pulsed structure of synchrotron-generated x-rays to create time-resolved images of magnetism at the nanoscale. In particular, we discuss how the presence of spin currents can be detected by imaging spin accumulation, and how the magnetisation dynamics in thin ferromagnetic films can be directly imaged. We discuss how a direct look at the phenomena allows for a deeper understanding of the the physics at play, that is not accessible to other, more indirect techniques. Finally, we present an overview of the exciting opportunities that lie ahead to further understand the fundamentals of novel spin physics, opportunities offered by the appearance of diffraction limited storage rings and free electron lasers.

  • 42. Brinkley, M. K.
    et al.
    Abergel, David S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Clader, B. D.
    Two-photon absorption in gapped bilayer graphene with a tunable chemical potential2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 36, article id 365001Article in journal (Refereed)
    Abstract [en]

    Despite the now vast body of two-dimensional materials under study, bilayer graphene remains unique in two ways: it hosts a simultaneously tunable band gap and electron density; and stems from simple fabrication methods. These two advantages underscore why bilayer graphene is critical as a material for optoelectronic applications. In the work that follows, we calculate the one-and two-photon absorption coefficients for degenerate interband absorption in a graphene bilayer hosting an asymmetry gap and adjustable chemical potential-all at finite temperature. Our analysis is comprehensive, characterizing one-and two-photon absorptive behavior over wide ranges of photon energy, gap, chemical potential, and thermal broadening. The two-photon absorption coefficient for bilayer graphene displays a rich structure as a function of photon energy and band gap due to the existence of multiple absorption pathways and the nontrivial dispersion of the low energy bands. This systematic work will prove integral to the design of bilayer-graphene-based nonlinear optical devices.

  • 43. Brinkley, M. K.
    et al.
    Abergel, David S. L.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Clader, B. D.
    Two-photon absorption in gapped bilayer graphene with a tunable chemical potential2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 36, article id 365001Article in journal (Refereed)
    Abstract [en]

    Despite the now vast body of two-dimensional materials under study, bilayer graphene remains unique in two ways: it hosts a simultaneously tunable band gap and electron density; and stems from simple fabrication methods. These two advantages underscore why bilayer graphene is critical as a material for optoelectronic applications. In the work that follows, we calculate the one-and two-photon absorption coefficients for degenerate interband absorption in a graphene bilayer hosting an asymmetry gap and adjustable chemical potential-all at finite temperature. Our analysis is comprehensive, characterizing one-and two-photon absorptive behavior over wide ranges of photon energy, gap, chemical potential, and thermal broadening. The two-photon absorption coefficient for bilayer graphene displays a rich structure as a function of photon energy and band gap due to the existence of multiple absorption pathways and the nontrivial dispersion of the low energy bands. This systematic work will prove integral to the design of bilayer-graphene-based nonlinear optical devices.

  • 44.
    Bultmark, F.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Dewhurst, K.
    Singh, D. J.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Tests of the efficiency of an augmented distorted planewave basis in electronic structure calculations2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 23, p. 235241-Article in journal (Refereed)
    Abstract [en]

    An augmented distorted planewave plus local orbital basis set has been developed and implemented in a simple fashion in order to test its efficiency for electronic structure calculations. It is based on the idea of using distorted planewaves (Gygi 1993 Phys. Rev. B 48 11692) as basis functions in the interstitial region instead of ordinary planewaves, as in the usual linearized augmented planewave and augmented planewave plus local orbitals methods. This is shown to lead to a significantly more rapid convergence for open structures as well as a modestly improved convergence for close packed structures.

  • 45.
    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.

  • 46.
    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.

  • 47.
    Cao, Hui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ma, Jing
    Yi, Luo
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Conductance Oscillation in Dithiolated Oligoacene JunctionsIn: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648XArticle in journal (Refereed)
  • 48. Cao, Peiyu
    et al.
    Ni, Xiaodong
    Tian, Fuyang
    Varga, Lajos K.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab initio study of AlxMoNbTiV high-entropy alloys2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 7, article id 075401Article in journal (Refereed)
    Abstract [en]

    The AlxMoNbTiV (x = 0-1.5) high-entropy alloys (HEAs) adopt a single solid-solution phase, having the body centered cubic (bcc) crystal structure. Here we employ the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation to investigate the equilibrium volume, elastic constants, and polycrystalline elastic moduli of AlxMoNbTiV HEAs. A comparison between the ab initio and experimental equilibrium volumes demonstrates the validity and accuracy of the present approach. Our results indicate that Al addition decreases the thermodynamic stability of the bcc structure with respect to face-centered cubic and hexagonal close packed lattices. For the elastically isotropic Al0.4MoNbTiV HEAs, the valence electron concentration (VEC) is about 4.82, which is slightly different from VEC similar to 4.72 obtained for the isotropic Gum metals and refractory-HEAs.

  • 49. Cao, Peiyu
    et al.
    Ni, Xiaodong
    Tian, Fuyang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Univ Sci & Technol Beijing, Dept Phys, Beijing 100083, Peoples R China.
    Varga, Lajos K.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Inst Solid State Phys & Opt, Wigner Res Ctr Phys, Hungary.
    Ab initio study of AlxMoNbTiV high-entropy alloys2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 7, article id 075401Article in journal (Refereed)
    Abstract [en]

    The AlxMoNbTiV (x = 0-1.5) high-entropy alloys (HEAs) adopt a single solid-solution phase, having the body centered cubic (bcc) crystal structure. Here we employ the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation to investigate the equilibrium volume, elastic constants, and polycrystalline elastic moduli of AlxMoNbTiV HEAs. A comparison between the ab initio and experimental equilibrium volumes demonstrates the validity and accuracy of the present approach. Our results indicate that Al addition decreases the thermodynamic stability of the bcc structure with respect to face-centered cubic and hexagonal close packed lattices. For the elastically isotropic Al0.4MoNbTiV HEAs, the valence electron concentration (VEC) is about 4.82, which is slightly different from VEC similar to 4.72 obtained for the isotropic Gum metals and refractory-HEAs.

  • 50.
    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.

1234567 1 - 50 of 438
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