| 1. |
- Adell, Johan, et al.
(författare)
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Formation of epitaxial MnBi layers on (Ga,Mn)As
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 2469-9950 .- 2469-9969. ; 80:7
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Tidskriftsartikel (refereegranskat)abstract
- The initial growth of MnBi on MnAs-terminated (GaMn)As is studied by means of synchrotron-based photoelectron spectroscopy. From analysis of surface core-level shifts we conclude that a continued epitaxial MnBi layer is formed, in which the MnAs/MnBi interface occurs between As and Bi atomic planes. The well-defined 1×2 surface reconstruction of the MnAs surface is preserved for up to 2 ML of MnBi before clear surface degradation occurs. The MnBi layer appears to be free from intermixed As.
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| 2. |
- Adnane, Bouchaib, et al.
(författare)
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Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X.
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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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| 3. |
- Airiskallio, E., et al.
(författare)
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Tuning the surface chemistry of Fe-Cr by V doping
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:15
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Tidskriftsartikel (refereegranskat)abstract
- The reversal of the magnitudes of the bulk and surface chemical-potential differences induces the outburst of Cr on the otherwise pure Fe surface of Fe-Cr alloys. This threshold value for the Cr content is about 10 at. %. It is found that vanadium addition to Fe-Cr shifts the Cr threshold to a substantially lower value suggesting V having a positive effect on the corrosion resistance of low Cr steels. The obtained shift in the Cr threshold is shown to be connected to the change in volume of the alloy.
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| 4. |
- Alling, Björn, et al.
(författare)
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Effect of thermal expansion, electronic excitations, and disorder on the Curie temperature of Ni1-xCuxMnSb alloys
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:13
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the importance of thermal effects such as temperature-induced electronic, magnetic and vibrational excitations, as well as structural defects in the first-principles calculations of the magnetic critical temperature of complex alloys using half-Heusler Ni1-xCuxMnSb alloys as a case study. The thermal lattice expansion and one-electron excitations have been accounted for self-consistently in the Curie temperature calculations. In the Ni-rich region, electronic excitations, thermal expansion, and structural defects substantially decrease the calculated Curie temperature. At the same time, some defects are shown to increase T-C in Cu-rich samples.
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| 5. |
- Andreasson, Björn Pererik, 1979-, et al.
(författare)
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Detecting oxygen vacancies in SrTiO3 by 3d transition-metal tracer ions
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - College Park, MD : American Physical Society. - 1098-0121 .- 1550-235X. ; 80:21, s. Article number: 212103-
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption experiments on 3d transition-metal tracer ions in SrTiO3 are presented. The absorption spectra of the tracer-ion changed upon reduction in the SrTiO3. This change is due to an oxygen vacancy created at the tracer-ion site. This finding is supported by density-functional theory calculations, which prove that the oxygen vacancies preferentially are created at the tracer-ion sites. Using the chemical sensitivity of x-ray absorption spectroscopy, tracer ions can be used to detect oxygen vacancies in SrTiO3 and possibly in other oxide systems. © 2009 The American Physical Society.
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| 6. |
- Andreasson, Jakob, 1975, et al.
(författare)
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Electron-lattice interactions in the perovskite LaFe0.5Cr0.5O3 characterized by optical spectroscopy and LDA plus U calculations
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 80:7, s. 075103-
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Tidskriftsartikel (refereegranskat)abstract
- We use resonance Raman scattering (incident photon energies between 1.8 and 4.13 eV), LDA+U calculations, spectroscopic ellipsometry, and oblique IR reflectivity to characterize the strong electron-phonon interactions in the disordered perovskite LaFe0.5Cr0.5O3. When the photon energy coincides with a Cr to Fe Mott-Hubbard transfer gap around 2.4 eV the electron-phonon interaction is manifested by a Franck-Condon effect with exceptional first-and higher order scattering of a local oxygen breathing mode. At higher incident energies we observe a superposition of Franck-Condon scattering and Frohlich interaction induced infrared active longitudinal optical two-phonon scattering activated mainly by O to Fe charge transfer. Our results establish LaFe0.5Cr0.5O3 as a model compound for research on electron-phonon interactions in strongly correlated complex systems and show that Franck-Condon scattering in complex solids is not limited to Jahn-Teller active compounds.
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| 7. |
- Araujo, C. M., et al.
(författare)
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Superionicity in the hydrogen storage material Li2NH : Molecular dynamics simulations
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:17
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Tidskriftsartikel (refereegranskat)abstract
- We have employed ab initio molecular dynamics simulations in an attempt to study a temperature-induced order-disorder structural phase transformation that occurs in Li2NH at about 385 K. A structural phase transition was observed by us in the temperature range 300-400 K, in good agreement with experiment. This transition is associated with a melting of the cation sublattice (Li+), giving rise to a superionic phase, which in turn is accompanied by an order-disorder transition of the N-H bond orientation. The results obtained here can contribute to a better understanding of the hydrogen storage reactions involving Li2NH and furthermore broaden its possible technological applications toward batteries and fuel cells.
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| 8. |
- Asker, Christian, et al.
(författare)
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Elastic constants and anisotropy in FeNi alloys at high pressures from first-principles calculations
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:21
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Tidskriftsartikel (refereegranskat)abstract
- The single-crystal and polycrystalline elastic constants and the elastic anisotropy in face-centered cubic and hexagonal close-packed FeNi alloys have been investigated at ultrahigh pressures by means of first-principles calculations using the exact muffin-tin orbitals method and the coherent-potential approximation. Comparisons with earlier calculations for pure Fe and experimental results are presented and discussed. We show that Ni alloying into Fe increases slightly the density and has very little effect on bulk moduli. Moreover, the relative decrease in c(44) elastic constant is much stronger in the hcp phase than in the fcc one. It is found that the elastic anisotropy is higher for face-centered cubic than for the hexagonal close-packed structure of FeNi, even though the face-centered cubic phase has a higher degree of symmetry. The anisotropy in face-centered cubic structure decreases with increasing nickel concentration while a very weak increase is observed for the hexagonal close-packed structure.
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| 9. |
- Babaev, Egor
(författare)
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Non-Meissner electrodynamics and knotted solitons in two-component superconductors
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:10
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Tidskriftsartikel (refereegranskat)abstract
- I consider electrodynamics and the problem of knotted solitons in two-component superconductors. Possible existence of knotted solitons in multicomponent superconductors was predicted several years ago. However, their basic properties and stability in these systems remain an outstandingly difficult question both for analytical and numerical treatment. Here I propose a special perturbative approach to treat self-consistently all the degrees of freedom in the problem. I show that there exists a length scale for a Hopfion texture where the electrodynamics of a two-component superconductor is dominated by a self-induced Faddeev term, which is in stark contrast to the Meissner electrodynamics of single-component systems. I also show that at certain short length scales knotted solitons in the two-component Ginzburg-Landau model are not described by a Faddeev-Skyrme-type model and are unstable. However, these solitons can be stable at some intermediate length scales. I argue that configurations with high topological charge may be more stable in these systems than low-charge configurations. In the second part of the paper I discuss qualitatively different physics of the stability of knotted solitons in a more general Ginzburg-Landau model and point out the physically relevant terms which enhance or suppress the stability of knotted solitons. With this argument it is demonstrated that Ginzburg-Landau models possess stable knotted solitons.
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| 10. |
- Balkashin, O. P., et al.
(författare)
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Spin dynamics in point contacts to single ferromagnetic films
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:9, s. 092419-1-092419-4
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Tidskriftsartikel (refereegranskat)abstract
- Excitation of magnons or spin waves driven by nominally unpolarized transport currents in point contacts of normal and ferromagnetic metals is probed by irradiating the contacts with microwaves. Two characteristic dynamic effects are observed: a suppression of spin-wave nonlinearities in the point contact conductance by off-resonance microwave irradiation and a resonant stimulation of spin-wave peaks in the differential resistance of the nanocontacts by the microwave field. These observations provide direct evidence that the magnetoresistance peaks observed are due to gigahertz spin dynamics at the ferromagnetic interface driven by the spin transfer torque effect of the transport current.
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