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  • 1.
    Bengone, Oliver
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Eriksson, O
    Fransson, J
    Turek, I
    Kudrnovsky, J
    Drchal, V
    Electronic structure and transport properties of CrAs/GaAs/CrAs trilayers from first principles theory2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 3, p. 035302-Article in journal (Refereed)
    Abstract [en]

    We present a theoretical study of the transport properties of a CrAs/GaAs/CrAs trilayer. The theory was based on a first principles method for calculating the electronic structure, in combination with a Kubo-Landauer approach for calculating the transport properties in a current perpendicular to the plane geometry. We have also investigated the electronic structure and the magnetic properties of this trilayer, with special focus on electronic and magnetic properties at the CrAs/GaAs interface. Finally, we have studied the effects of chemical disorder on the transport properties, in particular the influence of As antisites at both the Cr and Ga sites.

  • 2.
    Bengone, Oliver
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Eriksson, O
    Mirbt, S
    Turek, I
    Kudrnovsky, J
    Drchal, V
    Origin of the negative giant magnetoresistance effect in Co1-xCrx/Cu/Co (111) trilayers2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 9, p. 092406-Article in journal (Refereed)
    Abstract [en]

    We present a theoretical study on Co1-xCrx/Cu/Co (111) trilayers, where a transition from positive to negative giant magnetoresistance effect has been observed experimentally, with increasing thickness of the alloyed layer. The theory, based on a recently implemented conductance calculation, reproduces quantitatively this observation, and the effect is found to be caused by alloying effects, due to a virtual bound Cr d state in the majority spin channel of the Co-Cr layer.

  • 3.
    Castleton, C W M
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Mirbt, S
    Finite-size scaling as a cure for supercell approximation errors in calculations of neutral native defects in InP2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 19, p. 195202-Article in journal (Refereed)
    Abstract [en]

    The relaxed and unrelaxed formation energies of neutral antisites and interstitial defects in InP are calculated using ab initio density functional theory and simple cubic supercells of up to 512 atoms. The finite-size errors in the formation energies of all the neutral defects arising from the supercell approximation are examined and corrected for using finite-size scaling methods, which are shown to be a very promising approach to the problem. Elastic errors scale linearly, while the errors arising from charge multipole interactions between the defect and its images in the periodic boundary conditions have a linear plus a higher order term, for which a cubic provides the best fit. These latter errors are shown to be significant even for neutral defects. Instances are also presented where even the 512 atom supercell is not sufficiently converged. Instead, physically relevant results can be obtained only by finite-size scaling the results of calculations in several supercells, up to and including the 512 atom cell and in extreme cases possibly even including the 1000 atom supercell.

  • 4.
    Castleton, CWM
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Höglund, A
    Theory of Condensed Matter, Department of Physics, Uppsala University, Uppsala.
    Mirbt, S
    Theory of Condensed Matter, Department of Physics, Uppsala University, Uppsala.
    Managing the supercell approximation for charged defects in semiconductors: Finite-size scaling, charge correction factors, the band-gap problem, and the ab initio dielectric constant2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 3, article id 035215Article in journal (Refereed)
    Abstract [en]

    The errors arising in ab initio density functional theory studies of semiconductor point defects using the supercell approximation are analyzed. It is demonstrated that (a) the leading finite size errors are inverse linear and inverse cubic in the supercell size and (b) finite size scaling over a series of supercells gives reliable isolated charged defect formation energies to around +/- 0.05 eV. The scaled results are used to test three correction methods. The Makov-Payne method is insufficient, but combined with the scaling parameters yields an ab initio dielectric constant of 11.6 +/- 4.1 for InP. Gamma point corrections for defect level dispersion are completely incorrect, even for shallow levels, but realigning the total potential in real-space between defect and bulk cells actually corrects the electrostatic defect-defect interaction errors as well. Isolated defect energies to +/- 0.1 eV are then obtained using a 64 atom supercell, though this does not improve for larger cells. Finally, finite size scaling of known dopant levels shows how to treat the band gap problem: in <= 200 atom supercells with no corrections, continuing to consider levels into the theoretical conduction band (extended gap) comes closest to experiment. However, for larger cells or when supercell approximation errors are removed, a scissors scheme stretching the theoretical band gap onto the experimental one is in fact correct.

  • 5. Holmlund, Joakim
    et al.
    Andreasson, Jakob
    Knee, Christopher S.
    Bäckström, Joakim
    Kall, Mikael
    Osada, Minoru
    Noji, Takashi
    Koike, Yoji
    Kakihana, Masato
    Borjesson, Lars
    Resonant two-phonon Raman scattering as a probe of hole crystal formation in Sr14-xCaxCu24O412006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74Article in journal (Refereed)
    Abstract [en]

    The charge dynamics of the spin ladder compound Sr14-xCaxCu24O41 with x=0,6,13.6 has been investigated using wavelength- and temperature-dependent phonon Raman scattering on single crystals. In the unsubstituted, x=0, compound, a set of sharp two-phonon lines shows a strong increase in intensity below T similar to 200 K for light polarized along the ladder layer and with excitation energy close to the charge transfer gap similar to 1.9 eV. The temperature dependence of the strongly enhanced two-phonon bands below 200 K closely follows the recently reported formation of a standing charge density wave in the ladders [P. Abbamonte , Nature 431, 1078 (2004)]. Upon calcium substitution the polarized resonant Raman response rapidly decreases, signaling an increase of hole mobility in the ladder units. Temperature-dependent measurements of the x=13.6 sample indicate mobility of holes down to < 8 K.

  • 6. Hristopulos, D.
    et al.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Structural disorder effects on the tensile strength distribution of heterogeneous brittle materials with emphasis on fiber networks2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 6, p. 64108-Article in journal (Refereed)
  • 7. Kim, J J
    et al.
    Olin, Håkan
    Department of Physics, Chalmers University of Technology.
    Atomic- and electronic-structure study on the layers of 4Hb-TaS2 prepared by a layer-by-layer etching technique1995In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 52, no 20, p. 14388-14391Article in journal (Refereed)
    Abstract [en]

    We have studied the atomic and electronic structures of 4Hb-TaS2, which has alternating layers of the 1T and 1H type, at room temperature and 77 K, using a scanning tunneling microscope. Using a layer-by-layer etching technique, we fabricated staircases with alternating layers of the 1T and 1H type. The T-type layers showed the typical √13×√13 charge-density-wave structures, whereas the H-type layers had the triangular atomic structure at both temperatures. The measured tunneling spectra of each layer at 77 K showed entirely different characteristics; the 1H layer remained in the metallic state, whereas the 1T layer showed an insulating behavior with a wide opening of the energy gap at the Fermi level at 77 K.

  • 8. Kovalskii, VA
    et al.
    Gubarev, SI
    Kukushkin, IV
    Mikhailov, Sergey A
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Smet, JH
    von Klitzing, K
    Wegscheider, W
    Microwave response of two-dimensional electron rings2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 19Article in journal (Refereed)
  • 9. Le Bacq, O
    et al.
    Pasturel, A
    Bengone, Oliver
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Impact on electronic correlations on the structural stability, magnetism, and voltage of LiCoPO4 battery2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 24, p. 245107-Article in journal (Refereed)
    Abstract [en]

    We present a study of the structural stability of the lithium-orthophosphate oxide LiCoPO4 using density-functional theory within the local-density (LDA), generalized gradient and LDA+U approximation. We show that both enhanced localization and anisotropic effects provided within the LDA+U approximation are essential to reproduce the experimentally observed magnetic structure, lattice parameters, and stability of the lithiated and nonlithiated compound. Within this approximation, the intercalation voltage of 4.6 eV as well as the insulator character of the lithiated and nonlithiated compounds are recovered. Moreover, we found that the LDA+U approximation induces a strong transfer of charge from the t(2g)-like to the e(g)-like orbitals of Co as well as a significant shift of the LiPO4 band. Both effects are competing with each other and determine most of the peculiar properties of the LiCoPO4 and CoPO4 compounds.

  • 10.
    Mikhailov, Sergey A
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Microwave-induced magnetotransport phenomena in two-dimensional electron systems: Importance of electrodynamic effects2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 16, p. 165311-Article in journal (Refereed)
    Abstract [en]

    We discuss possible origins of recently discovered microwave induced photoresistance oscillations in very-high-electron-mobility two-dimensional electron systems. We show that electrodynamic effects-the radiative decay, plasma oscillations, and retardation effects-are important under the experimental conditions, and that their inclusion in the theory is essential for understanding the discussed and related microwave induced magnetotransport phenomena.

  • 11.
    Mikhailov, Sergey A
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Savostianova, N A
    Microwave response of a two-dimensional electron stripe2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71§, no 3, p. 035320-Article in journal (Refereed)
    Abstract [en]

    Electromagnetic response of a finite-width two-dimensional electron stripe is theoretically studied. It is shown that retardation and radiative effects substantially modify the absorption spectrum of the system at microwave frequencies, leading to a nontrivial zigzag behavior of the magnetoplasmon-polariton modes in magnetic fields, similar to that recently observed by Kukushkin [Phys. Rev. Lett. 90, 156801 (2003)].

  • 12.
    Mikhailov, Sergey
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Savostianova, N.A.
    Influence of contacts on the microwave response of a two-dimensional electron stripe2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 4, article id 045325Article in journal (Refereed)
    Abstract [en]

    Electromagnetic response of a finite-width two-dimensional electron stripe with attached metallic side contacts is theoretically studied. It is shown that contacts substantially influence the position, the linewidth, and the amplitude of plasmon-polariton resonances in the stripe. In finite magnetic fields, absorption of the wave with the inactive circular polarization (which is not absorbed in an infinite system without contacts) may become larger than that of the wave with the active polarization. The results are discussed in view of recent microwave experiments in two-dimensional electron systems.

  • 13.
    Ning, Lixin X
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Mak, C. S. K.
    Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
    Tanner, P. A.
    Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
    High-spin and low-spin f-d transitions of Tb3+ in elpasolite hosts2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 8, article id 085127Article in journal (Refereed)
    Abstract [en]

    The electronic absorption spectra of Cs2NaTbCl6 and Cs2NaYCl6:Tb3+ have been recorded between 34000-43000 cm(-1) at temperatures down to 10 K. Well-resolved spin-forbidden and spin-allowed transitions are observed, comprising three and one electronic transitions, respectively, between the crystal field levels of 4f(8) and 4f(7)d (t(2g)) states. For transitions from the electronic ground state, symmetry selection rules restrict the upper crystal field levels to be Gamma(4u) (T-1u) symmetry. Three vibrational progression modes appear in the electronic transitions and these are assigned to breathing modes with the first, second, and third nearest neighbors of Tb3+. The experimental results are rationalized both from the use of a simple model and from the extended f-shell programs of Reid. The excitation process 4f(8)-> 4f(7)5d (t(2g)) involves a small (5.5 pm) bond length change which is considered to be a contraction rather than an expansion.

  • 14. Wilkins, S B
    et al.
    Stojic, N
    Beale, T A W
    Binggeli, N
    Castleton, C W M
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bencok, P
    Prabhakaran, D
    Boothroyd, A T
    Hatton, P D
    Altarelli, M
    Resonant soft x-ray scattering investigation of orbital and magnetic ordering in La0.5Sr1.5MnO42005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 24, p. 245102-Article in journal (Refereed)
    Abstract [en]

    We report resonant x-ray scattering data of the orbital and magnetic ordering at low temperatures at the Mn L-2,L-3 edges in La0.5Sr1.5MnO4. The orderings display complex energy features close to the Mn absorption edges. Systematic modeling with atomic multiplet crystal field calculations was used to extract meaningful information regarding the interplay of spin, orbital, and Jahn-Teller order. These calculations provide a good general agreement with the observed energy dependence of the scattered intensity for a dominant orbital ordering of the d(x)(2)-z(2)/d(y)(2)-z(2) type. In addition, the origins of various spectral features are identified. The temperature dependence of the orbital and magnetic ordering was measured and suggests a strong interplay between the magnetic and orbital order parameters.

  • 15.
    Åberg, Daniel
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Edvardsson, Sverker
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Engholm, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Direct calculation of correlated absorption amplitudes for Nd:LiYF42003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 19, article id 195105Article in journal (Refereed)
    Abstract [en]

    The correlation contribution to the transition amplitudes are investigated in the case of Nd:LiYF4. By using many-body perturbation theory, we derive expressions for an effective dipole operator. The operators considered are Omega(es)((1)dagger)DOmega(cf)((1)), Omega(cf)((1)dagger)DOmega(es)((1)), Omega(es-cf)((2)dagger)D, and DOmega(es-cf)((2)). In contrast to third-order spin-orbit and crystal-field modified amplitudes, inclusion of correlation modifies the standard second-order amplitudes significantly. A model cluster is optimized to experimental energy levels. This approach is then used to compute consistent odd and even crystal-field parameters needed for theoretical absorption spectra. As expected, it is observed that transitions occurring at small wavelengths are quite heavily influenced by correlation. The overall agreement between experimental and theoretical spectra below 600 nm (above 17000 cm(-1)) is greatly improved when correlation is taken into account.

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