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Sökning: L773:1098 0121

  • Resultat 11-20 av 2117
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11.
  • Adell, M, et al. (författare)
  • Photoemission studies of the annealing-induced modifications of Ga0.95Mn0.05As
  • 2004
  • Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:12: 125204
  • Tidskriftsartikel (refereegranskat)abstract
    • Using angle resolved photoemission we have investigated annealing-induced changes in Ga1-xMnxAs with x=0.05. We find that the position of the Fermi energy is a function of annealing time and temperature. It is also established that the Curie temperature is strongly correlated to the separation between the Fermi level and the valence band maximum. Valence band photoemission shows that the Mn3d spectrum is modified by the annealing treatments.
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12.
  • Adey, J., et al. (författare)
  • Theory of boron-vacancy complexes in silicon
  • 2005
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:16, s. 165211-
  • Tidskriftsartikel (refereegranskat)abstract
    • The substitutional boron-vacancy BsV complex in silicon is investigated using the local density functional theory. These theoretical results give an explanation of the experimentally reported, well established metastability of the boron-related defect observed in p-type silicon irradiated at low temperature and of the two hole transitions that are observed to be associated with one of the configurations of the metastable defect. BsV is found to have several stable configurations, depending on charge state. In the positive charge state the second nearest neighbor configuration with C1 symmetry is almost degenerate with the second nearest neighbor configuration that has C1h symmetry since the bond reconstruction is weakened by the removal of electrons from the center. A third nearest neighbor configuration of BsV has the lowest energy in the negative charge state. An assignment of the three energy levels associated with BsV is made. The experimentally observed Ev+0.31 eV and Ev+0.37 eV levels are related to the donor levels of second nearest neighbor BsV with C1 and C1h symmetry respectively. The observed Ev+0.11 eV level is assigned to the vertical donor level of the third nearest neighbor configuration. The boron-divacancy complex BsV2 is also studied and is found to be stable with a binding energy between V2 and Bs of around 0.2 eV. Its energy levels lie close to those of the V2. However, the defect is likely to be an important defect only in heavily doped material.
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13.
  • Adnane, Bouchaib, et al. (författare)
  • Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots
  • 2009
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • A normal incidence photodetector operating at 8-14 μm is demonstrated using p-type δ-doped SiGe dot multilayer structures grown by molecular beam epitaxy on Si(001) substrates. Based on the experimental results of photoluminescence and photoluminescence excitation spectroscopies together with numerical analysis, the origin of the measured photocurrent was attributed to intersubband optical transitions between the heavy hole and light hole states of the valence band of the self-assembled SiGe dots and subsequent lateral transport of photo-excited carriers in the conduction channels formed by Ge wetting layers.
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14.
  • Adroja, D. T., et al. (författare)
  • Competing 4 f-electron dynamics in Ce(Ru1-xFex)(2)Al-10 (0
  • 2013
  • Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:22
  • Tidskriftsartikel (refereegranskat)abstract
    • We have carried out muon spin relaxation (mu SR), neutron diffraction, and inelastic neutron scattering (INS) investigations on polycrystalline samples of Ce(Ru1-xFex)(2)Al-10 (x = 0, 0.3, 0.5, 0.8, and 1) to investigate the nature of the ground state (magnetic ordered versus paramagnetic) and the origin of the spin-gap formation as evident from the bulk measurements in the end members. Our zero-field mu SR spectra clearly reveal coherent two-frequency oscillations at low temperature in x = 0, 0.3, and 0.5 samples, which confirm the long-range magnetic ordering of the Ce moment with Neel temperature T-N = 27, 26, and 21 K, respectively. On the other hand, the mu SR spectra of x = 0.8 and x = 1 down to 1.4 K and 0.045 K, respectively, exhibit a temperature-independent Kubo-Toyabe term, confirming a paramagnetic ground state. The long-range magnetic ordering in x = 0.5 below 21 K has been confirmed through the neutron diffraction study. INS measurements of x = 0 clearly reveal the presence of a sharp inelastic excitation near 8 meV between 5 K and 26 K, due to an opening of a gap in the spin excitation spectrum, which transforms into a broad response at and above 30 K. Interestingly, at 4.5 K, the spin-gap excitation broadens in x = 0.3 and exhibits two clear peaks at 8.4(3) and 12.0(5) meV in x = 0.5. In the x = 0.8 sample, which remains paramagnetic down to 1.2 K, there is a clear signature of a spin gap of 10-12 meV at 7 K, with a strong wave-vector-dependent intensity. Evidence of a spin gap of 12.5(5) meV has also been found in x = 1. The observation of a spin gap in the paramagnetic samples (x = 0.8 and 1) is an interesting finding in this study, and it challenges our understanding of the origin of the semiconducting gap in CeT2Al10 (T = Ru and Os) compounds in terms of a hybridization gap opening only a small part of the Fermi surface, gapped spin waves, or a spin-dimer gap.
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15.
  • Agterberg, Daniel F., et al. (författare)
  • Checkerboard order in vortex cores from pair-density-wave superconductivity
  • 2015
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:10
  • Tidskriftsartikel (refereegranskat)abstract
    • We consider competing pair-density-wave (PDW) and d-wave superconducting states in a magnetic field. We show that PDW order appears in the cores of d-wave vortices, driving checkerboard charge-density-wave (CDW) order in the vortex cores, which is consistent with experimental observations. Furthermore, we find an additional CDW order that appears on a ring outside the vortex cores. This CDW order varies with a period that is twice that of the checkerboard CDW and it only appears where both PDW and d-wave order coexist. The observation of this additional CDW order would provide strong evidence for PDW order in the pseudogap phase of the cuprates. We further argue that the CDW seen by nuclear magnetic resonance at high fields is due to a PDW state that emerges when a magnetic field is applied.
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16.
  • Agterberg, Daniel F., et al. (författare)
  • Microscopic prediction of skyrmion lattice state in clean interface superconductors
  • 2014
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:6, s. 064509-
  • Tidskriftsartikel (refereegranskat)abstract
    • When an in-plane field is applied to a clean interface superconductor, a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like phase is stabilized. This phase has a U(1)xU(1) symmetry and, in principle, this symmetry allows for flux carrying topological excitations different from Abrikosov vortices (which are the simplest defects associated with S-1 --> S-1 maps). However, in practice, largely due to electromagnetic and other intercomponent interactions, such topological excitations are very rare in superconducting systems. Here, we demonstrate that a realistic microscopic theory for interface superconductors, such as SrTiO3/LaAlO3, predicts an unconventional magnetic response where the flux-carrying objects are skyrmions, characterized by homotopy invariants of S-2 --> S-2 maps. Additionally, we show that this microscopic theory predicts that stable fractional vortices form near the boundary of these superconductors. It also predicts the appearance of type-1.5 superconductivity for some range of parameters. Central to these results is the assumption that the Rashba spin-orbit coupling is much larger than the superconducting gap.
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17.
  • Agåker, Marcus, et al. (författare)
  • Double core excitations in LiI : Evidence for multicenter coupling in resonant inelastic soft x-ray scattering spectra
  • 2006
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:24, s. 241105-
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonances in inelastic soft x-ray scattering spectra of LiI, in which final states with Li 1s as well as I 4d vacancies are populated have been observed. The intermediate states involve both Li 1s double core excitations and I parallel to 4p(-1)+4d(-2)4f > states. It is suggested that the spectra are influenced by multicenter coupling.
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18.
  • Agåker, Marcus, et al. (författare)
  • Double Core Excitations in Lithium Halides
  • 2007
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:4, s. 045112-
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant inelastic x-ray scattering spectra of LiF , LiCl , LiBr , and LiI excited in the vicinity of the Li double core hole resonances are presented. All lithium halides show similar phenomenology, including scattering via states where both excited electrons are localized during the scattering process, as well as states where one electron delocalizes. Also transitions that involve additional band excitations are observed. A strong influence of the chemical surrounding is found, and it is discussed in terms of the ionic character of the chemical bond.
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19.
  • Agåker, Marcus, et al. (författare)
  • Resonant inelastic soft x-ray scattering at double core excitations in solid LiCl
  • 2006
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:24
  • Tidskriftsartikel (refereegranskat)abstract
    • Inelastic soft x-ray scattering in LiCl, resonantly enhanced at states with two Li 1s vacancies, is investigated. States in which both excited electrons are localized during the double core hole lifetime, in which one of the electrons delocalize, as well as triply excited states in which the double core excitation is accompanied by a valence-to-conduction band excitation, contribute to the scattering. The angular momentum symmetry of the involved states and the vibronic coupling during the scattering process are reflected in the angular anisotropy. The effect on the local electronic structure of multiple core holes is theoretically studied by means of supercell band calculations.
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20.
  • Ahlberg, Martina, et al. (författare)
  • Influence of boundaries on magnetic ordering in Fe/V superlattices
  • 2010
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:21, s. 214429-
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the role of surface boundaries on the magnetic properties of [Fe/V](n) superlattice structures, with n=2-10. Using the magneto-optical Kerr effect and polarized neutron reflectivity measurements, we examine the evolution of both the total and the layer-resolved magnetizations as a function of temperature. By varying n, we observe a large shift in the transition temperatures T-c and a substantial change in the total magnetization critical exponent beta. In particular, the thicker samples exhibit nonuniversal exponent values. By resolving the magnetization as a function of position within the superlattice, we show that this behavior arises from contributions of the surfaces. Furthermore, we attribute the large shift in T-c to long-ranged interactions present in the superlattice.
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