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  • 1.
    Alling, Björn
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    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.
    Energetics and magnetic impact of 3d-metal doping of the half-metallic ferromagnet NiMnSb2008In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 77, no 14, p. 144414-Article in journal (Refereed)
    Abstract [en]

    We have performed a theoretical study of the effect of doping the half-Heusler alloy NiMnSb with the magnetic 3d metals Cr, Mn, Fe, Co, and Ni, with respect to both energetics and magnetic properties. Starting from the formation energies, we discuss the possibility of placing the dopant on different crystallographic positions in the alloy. We calculate total and local magnetic moments, effective exchange interactions, and density of states and also outline strategies to tune the magnetic properties of the alloy. Doping of NiMnSb with Cr as well as substituting some Ni with extra Mn have the largest impact on magnetic interactions in the system while preserving its half-metallic property. Therefore, we suggest the possibility that these dopants increase the thermal stability of half-metallicity in NiMnSb, with implications for its possible usage in spintronics applications.

  • 2.
    Bobbert, PA
    et al.
    COBRA Interuniversitary Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Wieldraaijer, H
    COBRA Interuniversitary Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    van der Weide, R
    COBRA Interuniversitary Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Kemerink, Martijn
    COBRA Interuniversitary Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Koenraad, PM
    COBRA Interuniversitary Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Wolter, JH
    COBRA Interuniversitary Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Exchange-correlation energy of a hole gas including valence band coupling1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 56, no 7, p. 3664-3671Article in journal (Refereed)
    Abstract [en]

    We have calculated an accurate exchange-correlation energy of a hole gas, including the complexities related to the valence band coupling as occurring in semiconductors like GaAs, but excluding the band warping. A parametrization for the dependence on the density and the ratio between light-and heavy-hole masses is given. We apply our results to a hole gas in an AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well and calculate the two-dimensional band structure and the band-gap renormalization. The inclusion of the valence band coupling in the calculation of the exchange-correlation potentials for holes and electrons leads to a much better agreement between theoretical and experimental data than when it is omitted.

  • 3.
    Buyanova, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Izadifard, Morteza
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Felici, M.
    Dipartimento di Fisica, Università di Roma “La Sapienza,” Roma, Italy .
    Polimeni, A.
    Dipartimento di Fisica, Università di Roma “La Sapienza,” Roma, Italy .
    Capizzi, M.
    Dipartimento di Fisica, Università di Roma “La Sapienza,” Roma, Italy .
    Hong, Y. G.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California, USA .
    Xin, H. P.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California, USA .
    Tu, C. W.
    Department of Electrical and Computer Engineering, University of California, La Jolla, California, USA .
    Direct experimental evidence for unusual effects of hydrogen on the electronic and vibrational properties of GaNxP1−x alloys: a proof for a general property of dilute nitrides2004In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, no 24, p. 245215-245219Article in journal (Refereed)
    Abstract [en]

    Direct experimental evidence for dramatic effects of hydrogen incorporation on the electronic structure and lattice properties of GaNxP1−x alloys is presented. By employing photoluminescence excitation spectroscopy, postgrowth hydrogenation is shown to reopen the band gap of the GaNP alloys and to efficiently reduce the N-induced coupling between the conduction band states. By Raman spectroscopy, these effects are shown to be accompanied by hydrogen-induced breaking of the Ga-P bond in the alloy, evident from disappearance of the corresponding vibrational mode. According to the performed Raman and x-ray diffraction measurements, the hydrogenation is also found to cause a strong expansion of the GaNP lattice, which changes the sign of strain from tensile in the as-grown GaNP epilayers to compressive in the posthydrogenated structures, due to the formation of complexes between N and H.

  • 4.
    Cao, C.
    et al.
    Physics Department, Illinois Institute of Technology, Chicago, Illinois, USA, Argonne Natl Lab, Div Mat Sci, Argonne, IL 60439 USA .
    Tao, R.
    Physics Department, University of Illinois at Chicago, Chicago, Illinois, USA.
    Ford, D.C.
    Materials Science Division, Argonne National Laboratory, Argonne, Illinois USA.
    Klie, R.
    Physics Department, University of Illinois at Chicago, Chicago, Illinois, USA.
    Proslier, T.
    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, USA.
    Cooley, L.
    Superconducting Materials Department, Technical Division, !Fermi National Accelerator Laboratory, Batavia, Illinois, USA.
    Dzyuba, A.
    Superconducting Materials Department, Technical Division, !Fermi National Accelerator Laboratory, Batavia, Illinois, USA.
    Zapol, P.
    Materials Science Division, Argonne National Laboratory, Argonne, Illinois, USA.
    Warren, M.
    Physics Department, Illinois Institute of Technology, Chicago, Illinois, USA.
    Lind, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Zasadzinski, J. F.
    Physics Department, Illinois Institute of Technology, Chicago, Illinois, USA.
    Giant two-phonon Raman scattering from nanoscale NbC precipitates in Nb2015In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 91, no 9, article id 094302Article in journal (Refereed)
    Abstract [en]

    High purity niobium (Nb), subjected to the processing methods used in the fabrication of superconducting RF cavities, displays micron-sized surface patches containing excess carbon. High-resolution transmission electron microscopy and electron energy-loss spectroscopy measurements are presented which reveal the presence of nanoscale NbC coherent precipitates in such regions. Raman backscatter spectroscopy on similar surface regions exhibit spectra consistent with the literature results on bulk NbC but with significantly enhanced two-phonon scattering. The unprecedented strength and sharpness of the two-phonon signal has prompted a theoretical analysis, using density functional theory (DFT), of phonon modes in NbC for two different interface models of the coherent precipitate. One model leads to overall compressive strain and a comparison to ab-initio calculations of phonon dispersion curves under uniform compression of the NbC shows that the measured two-phonon peaks are linked directly to phonon anomalies arising from strong electron-phonon interaction. Another model of the extended interface between Nb and NbC, studied by DFT, gives insight into the frequency shifts of the acoustic and optical mode density of states measured by first order Raman. The exact origin of the stronger two-phonon response is not known at present but it suggests the possibility of enhanced electron-phonon coupling in transition metal carbides under strain found either in the bulk NbC inclusions or at their interfaces with Nb metal. Preliminary tunneling studies using a point contact method show some energy gaps larger than expected for bulk NbC.

  • 5.
    da Silva, AF
    et al.
    Inst Nacl Pesquisas Espaciais, Lab Associado Sensores & Mat, LAS, BR-12201970 Sao Jose Dos Campos, Brazil Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Fed Rio Grande Sul, Inst Fis, BR-91501970 Porto Alegre, RS, Brazil CUNY City Coll, Dept Phys, New York, NY 10031 USA.
    Sernelius, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics .
    de Souza, JP
    Inst Nacl Pesquisas Espaciais, Lab Associado Sensores & Mat, LAS, BR-12201970 Sao Jose Dos Campos, Brazil Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Fed Rio Grande Sul, Inst Fis, BR-91501970 Porto Alegre, RS, Brazil CUNY City Coll, Dept Phys, New York, NY 10031 USA.
    Boudinov, H
    Inst Nacl Pesquisas Espaciais, Lab Associado Sensores & Mat, LAS, BR-12201970 Sao Jose Dos Campos, Brazil Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Fed Rio Grande Sul, Inst Fis, BR-91501970 Porto Alegre, RS, Brazil CUNY City Coll, Dept Phys, New York, NY 10031 USA.
    Zheng, HR
    Sarachik, MP
    Inst Nacl Pesquisas Espaciais, Lab Associado Sensores & Mat, LAS, BR-12201970 Sao Jose Dos Campos, Brazil Linkoping Univ, Dept Phys & Measurement Technol, S-58183 Linkoping, Sweden Univ Fed Rio Grande Sul, Inst Fis, BR-91501970 Porto Alegre, RS, Brazil CUNY City Coll, Dept Phys, New York, NY 10031 USA.
    Impurity resistivity of the double-donor system Si : P,Bi1999In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 60, no 23, p. 15824-15828Article in journal (Refereed)
    Abstract [en]

    The electrical resistivity of the shallow double-donor system Si:P,Bi, prepared by ion implantation, was investigated in the temperature range from 1.7 to 300 K. Good agreement was obtained between the measured resistivities and resistivities calculated by a generalized Drude approach for the same temperatures and dopant concentrations. The critical impurity concentration for the metal-nonmetal transition for the double-doped Si:P,Bi system was found to lie between the critical concentrations of the two single-doped systems, Si:P and Si:Bi. [S0163-1829(99)11747-8].

  • 6.
    Dagnelund, Daniel
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanova, Irina
    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.
    Murayama, A.
    Furuta, T.
    Hyomi, K.
    Souma, I.
    Oka, Y.
    Efficiency of optical spin injection and spin loss from a diluted magnetic semiconductor ZnMnSe to CdSe nonmagnetic quantum dots2008In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 77, no 3, p. 035437-Article in journal (Refereed)
    Abstract [en]

    Magneto-optical spectroscopy in combination with tunable laser spectroscopy is employed to study optical spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe into nonmagnetic CdSe quantum dots (QDs). Observation of a DMS feature in the excitation spectra of the QD photoluminescence polarization provides clear evidence for optical spin-injection from the DMS to the QDs. By means of a rate equation analysis, the injected spin polarization is deduced to be about 32% at 5 T, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process including crossing the heterointerfaces and energy relaxation within the QDs. © 2008 The American Physical Society.

  • 7.
    Eriksson, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Sakamoto, Kazuyuki
    Graduate School of Advanced Integrated Science Chiba University, Japan.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Lithium-induced dimer reconstructions on Si(001) studied by photoelectron spectroscopy and band-structure calculations2007In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 75, no 20, p. 205416-Article in journal (Refereed)
    Abstract [en]

    The electronic and atomic structure of Si(001) with 0.5 and 1 ML of lithium have been studied experimentally using angle resolved ultraviolet photoelectron spectroscopy, Si 2p core level spectroscopy, and low energy electron diffraction. Experimental surface state dispersions are compared with recent theoretical results in the literature and with results from additional density functional theory calculations. Four adsorption configurations for the 0.5 ML 2×2 surface and three configurations for the 1 ML 2×1 surface are compared. Fittings of Si 2p core level data support the alternation of strongly and weakly buckled Si dimers of the 2×2 models and symmetric Si dimers of the 2×1 models based on the relative intensities of the surface components. As a tool to differentiate between the different 2×2 and 2×1 models surface state dispersions are used since they are sensitive to the positions of the Li adatoms.

  • 8.
    Isaev, E.I.
    et al.
    Moscow Technological University.
    Ahuja, R.
    Uppsala University.
    Simak, Sergey
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Lichtenstein, A.I.
    Universität Hamburg.
    Vekilov, Yu. Kh.
    Moscow Technological University.
    Johansson, B.
    Uppsala University.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Anomalously enhanced superconductivity and ab initio lattice dynamics in transition metal carbides and nitrides2005In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 72, no 6, p. 4515-Article in journal (Refereed)
    Abstract [en]

    The lattice dynamics for the monocarbides and mononitrides of the early transition metals has been studied using first-principles density functional perturbation theory. It is shown that the superconductivity of transition metal carbides is directly related to anomalies in the phonon spectra which in their turn are connected to the number of valence electrons. The calculated electron-phonon interaction constants are in excellent agreement with experimental data. Superconductivity is considerably enhanced for substitutional M Cx N1-x alloys. We also predict that perfect VC in the sodium chloride structure (B1) is a superconductor with a transition temperature Tc =11.5 K. The experimental failure to sythesize some transition metal carbides and nitrides within the B1 structure is connected to their dynamical instability. © 2005 The American Physical Society.

  • 9.
    Järrendahl, Kenneth
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Dulea, Mihnea
    Institute for Physics and Technology of Materials, Bucharest-Magurele, Romania.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Sundgren, Jan- Erik
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    X-ray diffraction from amorphous Ge/Si Cantor superlattices1995In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 51, no 12, p. 7621-7631Article in journal (Refereed)
    Abstract [en]

    X-ray measurements on Cantor superlattices are reported. Indexing and scaling laws are derived for the distribution of peaks in the diffraction spectra of perfect superlattices. The peaks are indexed by three indices and the largest scaling exponents of the intensities are proportional to the fractal dimensions of the Cantor sets. The theoretical indexing scheme of the peaks is confirmed by experiment. The influence of the absorption and sample imperfections on the scaling of the peaks is investigated by means of numerical simulations. A discussion of the nature of the diffraction spectra in the thermodynamic limit is also included.

  • 10.
    Karis, O.
    et al.
    Uppsala University.
    Magnuson, Martin
    Université Pierre et Marie Curie, Paris.
    Wiell, T
    Uppsala University.
    Weinelt, M.
    Uppsala University.
    Wassdahl, N.
    Uppsala University.
    Nilsson, A.
    Uppsala University.
    Mårtensson, N.
    Uppsala University.
    Holmström, E.
    Uppsala University.
    Niklasson, A. M. N.
    Los Alamos National Laboratory, Los Alamos, New Mexico.
    Eriksson, Olle
    Uppsala University.
    Observation of short- and long-range hybridization of a buried Cu monolayer in Ni2000In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 62, no 24, p. R16239-R16242Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a Cu monolayer buried in Ni fcc(100) is studied by means of x-ray emission and absorption spectroscopies in combination with first principles calculations. The local character of the x-ray probes allows us to investigate changes in the chemical interaction for these ultrathin film systems. In comparison to bulk Cu, the occupied d states of a buried Cu monolayer, as mapped in the x-ray emission spectrum, remain mostly unaltered. The absorption spectrum on the other hand shows that the empty states of the buried Cu monolayer are modified, and instead resemble the unoccupied electronic density of bulk Ni. These findings agree well with our first principle electronic structure calculations and the results are interpreted in terms of short- and long-range hybridization.

  • 11.
    Kemerink, Martijn
    et al.
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Koenraad, PM
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Christianen, PCM
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    vanSchaijk, R
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Maan, JC
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Wolter, JH
    CATHOLIC UNIV NIJMEGEN, NETHERLANDS.
    Magneto-optical study on exciton screening in p-type AlxGa1-xAs/InyGa1-yAs quantum wells1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 56, no 8, p. 4853-4862Article in journal (Refereed)
    Abstract [en]

    We have studied exciton unbinding in empty and p-doped quantum wells, using magnetophotoluminescence excitation measurements. The use of p-type quantum wells allows us to discriminate unambiguously between exciton bleaching by Coulomb screening and by the Pauli exclusion principle. We found that the ground-state heavy-hole exciton, which experiences both effects, is unbound at hole densities in the range (6-9) x 10(15) m(-2). In contrast, the ground-state light-hole and first excited heavy-hole excitons, which are only screened by the Coulomb interaction, still have a finite binding energy at these densities. However, for both bands, its Value is far below what is found in an undoped well. Furthermore, we found a strong indication that, in p-doped wells, the excitons of excited subbands are less efficiently screened than those of the Light-hole ground state, due to the lesser overlap of the screening ground-state heavy holes with the excited subbands than with the ground-state light holes.

  • 12.
    Kemerink, Martijn
    et al.
    COBRA Interuniversity Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Koenraad, PM
    COBRA Interuniversity Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Wolter, JH
    COBRA Interuniversity Research Institute, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Effect of strain on a second-order van Hove singularity in AlxGa1-xAs/InyGa1-yAs quantum wells1996In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 54, no 15, p. 10644-10651Article in journal (Refereed)
    Abstract [en]

    We have performed low-temperature photoluminescence and photoluminescence excitation (PLE) measurements on highly degenerate p-type GaAs and InyGa1-yAs quantum wells. In the PLE spectrum of the GaAs well, evidence of a second-order van Hove singularity in the joint density of states of the ground-state light-hole and electron bands is found. This singularity results from the equality of ground-state light-hole and electron effective masses near the Gamma point, being a much more restrictive demand than the usual condition for a van Hove singularity, which requires only the equality of first derivatives of the subband dispersions. The second-order van Hove singularity gives rise to a power-law divergence at the singular point, whereas the corresponding usual van Hove singularity results in a steplike discontinuity in the joint density of states. The observed singularity could be described extremely well by a simple analytical model. The increased energy gap between light- and heavy-hole ground states in the compressively strained InyGa1-yAs well enhances the valence-band parabolicity, resulting in the disappearance of the van Hove singularity. Furthermore, it is shown that the anisotropic character of the heavy-hole ground state in GaAs is strongly suppressed in the InyGa1-yAs system. All experiments are in good agreement with our numerical modeling, based on an exact solution of the 4 x 4 Luttinger Hamiltonian.

  • 13.
    Linnarsson, M.
    et al.
    Royal Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kleverman, M.
    University of Lund.
    Thilderkvist, A.
    University of Lund.
    Electronic structure of the GaAs:MnGa center1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 55, no 11, p. 6938-6944Article in journal (Refereed)
    Abstract [en]

      n/a

     

  • 14.
    Magnuson, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Mattesini, Maurizio
    Universidad Complutense de Madrid.
    Van Nong, Ngo
    Technical University of Denmark.
    Eklund, Per
    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.
    Electronic-structure origin of the anisotropic thermopower of nanolaminated Ti3SiC2 determinedby polarized x-ray spectroscopy and Seebeck measurements2012In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 85, p. 195134-Article in journal (Refereed)
    Abstract [en]

    Nanolaminated materials exhibit characteristic magnetic, mechanical, and thermoelectric properties, withlarge contemporary scientific and technological interest. Here we report on the anisotropic Seebeck coefficient innanolaminated Ti3SiC2 single-crystal thin films and trace the origin to anisotropies in element-specific electronicstates. In bulk polycrystalline form, Ti3SiC2 has a virtually zero Seebeck coefficient over a wide temperaturerange. In contrast, we find that the in-plane (basal ab) Seebeck coefficient of Ti3SiC2, measured on single-crystalfilms, has a substantial and positive value of 4–6 μV/K. Employing a combination of polarized angle-dependentx-ray spectroscopy and density functional theory we directly show electronic structure anisotropy in inherentlynanolaminated Ti3SiC2 single-crystal thin films as a model system. The density of Ti 3d and C 2p states atthe Fermi level in the basal ab plane is about 40% higher than along the c axis. The Seebeck coefficient isrelated to electron and hole-like bands close to the Fermi level, but in contrast to ground state density functionaltheory modeling, the electronic structure is also influenced by phonons that need to be taken into account.Positive contribution to the Seebeck coefficient of the element-specific electronic occupations in the basal planeis compensated by 73% enhanced Si 3d electronic states across the laminate plane that give rise to a negativeSeebeck coefficient in that direction. Strong phonon vibration modes with three to four times higher frequencyalong the c axis than along the basal ab plane also influence the electronic population and themeasured spectra bythe asymmetric average displacements of the Si atoms. These results constitute experimental evidence explainingwhy the average Seebeck coefficient of Ti3SiC2 in polycrystals is negligible over a wide temperature range. Thisallows the origin of anisotropy in physical properties of nanolaminated materials to be traced to anisotropies inelement-specific electronic states.

  • 15.
    Magnuson, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Schmidt, Susann
    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.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Electronic properties and bonding in ZrHx thin films investigated by valence-bandx-ray photoelectron spectroscopy2017In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 96, no 19, article id 195103Article in journal (Refereed)
    Abstract [en]

    The electronic structure and chemical bonding in reactively magnetron sputtered ZrHx (x = 0.15, 0.30, 1.16)thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level,and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significantreduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H1s–Zr 4d hybridization region at ∼6 eV below the Fermi level. For low hydrogen content (x = 0.15, 0.30), thefilms consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ-ZrHx(CaF2-type structure) phases, while for x = 1.16, the films form single-phase ZrHx that largely resembles thatof stoichiometric δ-ZrH2 phase. We show that the cubic δ-ZrHx phase is metastable as thin film up to x = 1.16,while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated ZrH1.16film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4p3/2 and 3d5/2peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifiesa charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemicalshifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affectsthe conductivity by charge redistribution in the valence band.

  • 16.
    Münger, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    NOVOTNY, MA
    Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida .
    MOMENTUM-SPACE MONTE-CARLO RENORMALIZATION-GROUP PROCEDURE1991In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 44, no 9, p. 4314-4325Article in journal (Refereed)
    Abstract [en]

    We implement a momentum-space renormalization-group procedure into the Monte Carlo renormalization-group (MCRG) method. Usually the symmetries of the system must be known and incorporated into the renormalization group, but here we let the renormalization group be given by the Monte Carlo simulation itself This allows the MCRG method to be applicable to systems where the underlying symmetries may not be known, such as in Monte Carlo studies of quantum systems. As a test of this method, we apply it to the study of the two-dimensional square-lattice q-state Potts model, both for integer values of q and for noninteger values of q near q = 4.

  • 17.
    Münger, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    NOVOTNY, MA
    Supercomputer Computations Research Institute, Florida State University, Florida, USA .
    REWEIGHTING IN MONTE-CARLO AND MONTE-CARLO RENORMALIZATION-GROUP STUDIES1991In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 43, no 7, B, p. 5773-5783Article in journal (Refereed)
    Abstract [en]

    A method of reweighting Monte Carlo data to parameters other than the simulated ones is investigated. The method is also extended to include Monte Carlo renormalization-group simulations. Both single and multiple simulation reweighting is used. The models studied are the d = 2 ferromagnetic q = 3 Potts model and the d = 2 antiferromagnetic Ising model. It is shown that the reweighting produces a systematic shift in the height and location of the specific-heat peak. This shift, which without proper care may lead to erroneous results, depends on the simulated and reweighted temperatures and on the number of configurations included in the reweighting. Only for very large numbers of configurations does the shift decrease as the inverse square root of the number of configurations. Within the Monte Carlo renormalization-group study, it is shown that the critical exponents for the Ising model are determined more accurately from a multiple reweighting using one simulation below the critical temperature and one above than from the individual simulations. It is shown that it is more efficient to use two simulations at a time than all of them at once when reweighting multiple simulations.

  • 18.
    Nguyen, Son Tien
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Carlsson, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    ul-Hassan, Jawad
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Magnusson, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Defects and carrier compensation in semi-insulating 4H-SiC substrates2007In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 75, no 15Article in journal (Refereed)
    Abstract [en]

    Electron paramagnetic resonance (EPR) studies revealed that vacancies (VC and VSi), carbon vacancy-antisite pairs (VC CSi) and the divacancy (VC VSi) are common defects in high-purity semi-insulating (HPSI) 4H-SiC substrates. Their concentrations and some of their deep acceptor levels were estimated by EPR and photoexcitation EPR. The commonly observed thermal activation energies, Ea ∼0.8-0.9 eV, ∼1.1 eV, ∼1.25-1.3, and ∼1.5 eV, as determined from the temperature dependence of the resistivity, in different types of HPSI substrates were associated to different deep acceptor levels of VSi, VC, VC CSi, and VC VSi. The annealing behavior of these vacancy-related defects and their interaction at high temperatures (up to 1600°C) in HPSI materials were studied. Carrier compensation processes were proposed to explain the observed change of the thermal activation energy due to high temperature annealing. VC and VC VSi were suggested to be suitable defects for controlling the SI properties whereas the incorporation of VSi and VC CSi during the crystal growth or processing should be avoided for achieving stable HPSI materials. © 2007 The American Physical Society.

  • 19.
    Olovsson, W.
    et al.
    Uppsala University.
    Holmström, E.
    Los Alamos National Laboratory, New Mexico, USA.
    Wills, J.
    Los Alamos National Laboratory, New Mexico, USA.
    James, P.
    SKF Group MDC, Göteborg.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Niklasson, A.M.N.
    Los Alamos National Laboratory, New Mexico, USA.
    Relationship between the electronic structure of embedded single to triple atomic monolayers and bulk alloys2005In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 72, no 15, p. 5419-Article in journal (Refereed)
    Abstract [en]

    The relation between the electronic structure of thin film nanosandwiches and bulk alloys has been investigated by means of first-principles electronic structure theory. The spin magnetization, layered projected spectral properties, and interface core-level shifts of Cu, Ni, Co, and Fe systems have been calculated. In order to compare thin films to bulk alloys, systems with equal average nearest-neighbor coordination have been compared. We find that the spin magnetization and interface core level shifts are closely related to bulk with the exception of the core level shifts in the Fe/Cu multilayers, which are more sensitive to the specific structure of the thin film geometry. The discrepancy is discussed in terms of interacting interface states in the Cu spacer. The experimental possibility of detecting embedded monolayers is also investigated. © 2005 The American Physical Society.

  • 20.
    Ponomareva, A.V.
    et al.
    Moscow Steel and Alloys Institute Moscow, Russia.
    Isaev, E.I.
    Moscow steel and Alloys Institute Moscow, Russia.
    Skorodumova, N.v.
    uppsala University, Uppsala.
    Vekilov, Yu. Kh.
    Moscow Steel and alloys Institute, Moscow Russia.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Surface segregation energy in bcc Fe-rich Fe-Cr alloys2007In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 75, no 24, p. 5406-Article in journal (Refereed)
    Abstract [en]

    The exact muffin-tin orbitals (EMTO) technique in conjunction with the coherent-potential approximation (CPA) as well as the projector-augmented-wave (PAW) method have been used to calculate the surface segregation energy of Cr at the (100) surface of Fe-rich bcc Fe-Cr alloys. We find that PAW results strongly depend on the supercell size used in the calculations. In particular, for large supercells, the surface segregation energy of Cr is positive, which means that Cr should not segregate toward the surface of diluted alloys. This is in agreement with our EMTO-CPA results as well as previous surface Green's-function calculations. However, the surface segregation energy of Cr is negative if small unit cells are used for simulations. This is in agreement with previous full-potential supercell calculations. We explain such a size dependence by a peculiar concentration dependence of interatomic interactions in ferromagnetic Fe-Cr alloys. © 2007 The American Physical Society.

  • 21. Pourovskii, L.V.
    et al.
    Ruban, A.V.
    Vitos, L.
    Ebert, H.
    Johansson, B.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Fully relativistic spin-polarized exact muffin-tin-orbital method2005In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 71, no 9Article in journal (Refereed)
    Abstract [en]

    The exact muffin-tin-orbital (EMTO) method is generalized for fully relativistic (FR) spin-polarized calculations. In the present implementation we solve self-consistently the four-component Dirac equation by using the Green's function formalism. Substitutional disorder is treated within the coherent potential approximation. To obtain accurate total energies we use the full-charge density technique. We apply the FR-EMTO Green's function method to calculate the ground-state properties of δ-Pu. We also calculate spin and orbital magnetic moments in random bcc, fcc, and hcp Fe-Co alloys, as well as in the B2 ordered and partially ordered phase. ©2005 The American Physical Society.

  • 22.
    Ruban, A.V.
    et al.
    Department of Materials Science and Engineering Royal Institute of Technology, Stockholm.
    Katsnelson, M.I.
    Institute for Molecules and Materials Radboud University Nijmegen, The Netherlands.
    Olovsson, W.
    Condensed Matter Theory Group, Department of Physics Uppsala University.
    Simak, S.I.
    Condensed Matter Theory Group, Department of Physics Uppsala University.
    Abrikosov, Igor
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Origin of magnetic frustrations in Fe-Ni Invar alloys2005In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 71, no 5, p. 4402-Article in journal (Refereed)
    Abstract [en]

    Pair exchange parameters Jij of the classical Heisenberg Hamiltonian for magnetic interactions in the urchetypical Invar system, face centered cubic (fee) Fe-Ni alloys, are calculated from the first principles. The magnetic structure of Fe-Ni alloys in the region of volumes and electron concentrations related to the Invar effect is highly frustrated. However, the origin of such a frustration in concentrated alloys and in the pure fee Fe are different. While in Fe it is due to the long-range oscillating Jij, in alloys with high Ni concentration it is mainly the consequence of a huge dispersion of the nearest-neighbor exchange parameters, caused by the local environment effects. ©2005 The American Physical Society.

  • 23.
    Sakamoto, Kazuyuki
    et al.
    Graduate school of Advanced Integrated Science, Chiba University, Japan.
    Pick, Alexander
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Structural investigation of the quasi-one-dimensional reconstructions induced by Eu adsorption on a Si(111) surface2005In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 72, no 19, p. 195342-Article in journal (Refereed)
    Abstract [en]

    The surface structures of the (quasi-)one-dimensional reconstructions induced by the adsorption of Eu on Si(111) have been investigated by low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. Different phases were observed in LEED depending on the Eu coverage. The lowest coverage phase has a (3×2) periodicity, and the highest coverage phase has a (2×1) one. Of the intermediate phases, the LEED pattern of the so-called (5×1) surface indicates that this surface has actually a (5×4) periodicity. The Eu 4f core-level spectra show that the Eu coverages of the (3×2), (5×4), and (2×1) phases are 1∕6 monolayer (ML), 0.3 ML, and 0.5 ML, respectively, and that the valence state of the adsorbate is 2+ in all these three phases. In the Si 2p core-level spectra, three surface components were observed in both the lowest and highest coverage phases. By considering the energy shift and intensity of each surface component, we conclude that the structure of the (3×2) phase is basically the same as that of the honeycomb-chain-channel model, and that the (2×1) phase is formed by π-bonded Seiwatz Si chains. Regarding the (5×4) phase, two extra Si 2p surface components were observed together with the three components observed in the two end phases. Taking the energy shifts and intensities of the extra surface components into account, we propose a structural model of the (5×4) phase.

  • 24.
    Sakamoto, Kazuyuki
    et al.
    Department of Physics, Graduate School of Science, Tohoku University, Japan.
    Zhang, Hanmin
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, The Institute of Technology.
    Photoemission study of metastable oxygen adsorbed on a Si(111)-(7×7) surface2004In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, no 3, p. 035301-Article in journal (Refereed)
    Abstract [en]

    We have investigated the metastable oxygen species adsorbed on a Si(111)-(7×7) surface at room temperature using real time valence-band and core-level photoemission measurements. The dosage- and time-dependent changes in the intensity of the metastable 3.8 eV peak observed in the valence-band spectra were different from those of the metastable O 1s components. Further, although no metastable O 1s components were observed in the core-level measurement after annealing the sample at 600 K, the 3.8 eV peak was still observed. These results indicate that both the stable and the metastable oxygen species produce the 3.8 eV valence-band peak, and we therefore conclude that the contradicting lifetimes reported in the literature result from a misinterpretation of the 3.8 eV peak.

  • 25.
    Wang, X. J.
    et al.
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, China .
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials. Linköping University, The Institute of Technology.
    Sub-millisecond dynamic nuclear spin hyperpolarization in a semiconductor: A case study from PIn antisite in InP2012In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 86, no 20, p. 205202-1-205202-6Article in journal (Refereed)
    Abstract [en]

    Optically detected magnetic resonance is employed to identify key factors governing dynamic nuclear polarization (DNP) in a semiconductor. We demonstrate that the extent of DNP can be efficiently controlled by varying lifetime of the localized electrons that transfer spin angular momentum to nuclei. The ultimate speed of a DNP process, on the other hand, is determined by the strength of hyperfine interaction that drives DNP. We show that about 50% nuclear spin polarization of a PIn antisite in InP can be achieved by shortening electron lifetime within a remarkably short time (<0.1 ms) due to strong hyperfine coupling.

1 - 25 of 25
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