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  • 1.
    Anderssson, Magnus
    et al.
    KTH, Superseded Departments, Physics.
    Rapp, Östen
    KTH, Superseded Departments, Physics.
    Tellgren, Roland
    Institutet för kemi, Uppsala Universitet.
    NEUTRON-DIFFRACTION STUDIES OF INTERATOMIC DISTANCES IN THE Y1-2XCAXTHXBA2CU3O7-DELTA SYSTEM1992In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 81, no 5, p. 425-429Article in journal (Refereed)
    Abstract [en]

    Neutron diffraction studies have been performed for three samples of Y(1-2x)Ca(x)Th(x)Ba2Cu3O7-delta with 0 less-than-or-equal-to x less-than-or-equal-to 0.1. With increasing x, a decreased puckering of the Cu-O planes is found. Changes in copper oxygen distances are generally small. Evidence is found for a small increase in the distance between Cu(1) and O(4) (on the cell edge) with increased CaTh concentration. An increased oxygen disorder is observed at x = 0.1.

  • 2.
    Araujo, Rafael B.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Scheicher, R. H.
    De Almeida, J. S.
    Ferreira Da Silva, A.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lithium transport investigation in LixFeSiO4: A promising cathode material2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 173, p. 9-13Article in journal (Refereed)
    Abstract [en]

    In this paper we investigate lithium mobility in both Li 2FeSiO4 and its half-lithiated state LiFeSiO4 considering an orthorhombic crystal structure. We find that the calculated activation energy of Li+ ions hopping between adjacent equilibrium sites predicts two least hindered diffusion pathways in both materials. One of them is along the [100] direction characterizing an ionic diffusion in a straight line and the other follows a zig-zag way between the Fe-Si-O layers. We also show that diffusion of Li+ ions in the half-lithiated structure follows the same behavior as in the lithiated structure. As a whole, the activation energies for the investigated compounds present a greater value compared with the activation energies in currently used materials such as LiFePO4. The results were calculated in the framework of density functional theory in conjunction with the climbing image nudged elastic band method. The Hubbard term was added to the Kohn-Sham Hamiltonian to overcome the delocalization problem of d electrons. Furthermore, the diffusion coefficients were calculated for both structures considering temperatures ranging from 300 to 700 K.

  • 3. Cherian, R.
    et al.
    Mahadevan, P.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Role of Coulomb interactions in semicore levels Ga d levels of GaX semiconductors: Implication on band offsets2009In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 149, no 41-42, p. 1810-1813Article in journal (Refereed)
    Abstract [en]

    The positions of the semicore Ga d levels in GaX semiconductors (X = N, P, and As) are underestimated in density functional calculations using either the local density approximation LIDA or the generalized gradient approximation GGA for the exchange functional. Correcting for this inaccuracy within LDA + U calculations with an on-site Coulumb interaction U on the semicore d-states results in a modest enhancement of the band gap. We show that this modest enhancement of the band-gap energy comes from the movement of the valence-band maximum alone, thus not affecting the conduction-band states. Further, the localization of the charge on Ga d states with U leads to a regulation of charge on Ga. This yields a shift of 1-2 eV of the core levels on the Ga atom while the anion core levels remain unchanged.

  • 4. Chung, S. J.
    et al.
    Shin, D. Y.
    Son, H.
    Lee, S.
    Liu, X.
    Furdyna, J. K.
    Time stability of multi-domain states formed in the magnetization reversal process of GaMnAs film2007In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 143, no 4-5, p. 232-235Article in journal (Refereed)
    Abstract [en]

    The magnetization reversal process of ferromagnetic GaMnAs epilayers has been systematically investigated using the planar Hall effect (PHE) and magnetoresistance (MR). We have observed non-abrupt transitions between two orientations of magnetization in PHE and striking resistance dips at the second switching in MR. The observed behaviors indicate that multi-domain structures are formed as magnetization undergoes a reorientation. An asymmetric PHE hysteresis loop was obtained when the range of the field scan was restricted to fields below the final magnetization transition. This indicates that the domain structure formed at the moment of magnetization reorientation remains stable even after the magnetic field is removed. The time stability of the multi-domain structure was further tested by monitoring the change in the planar Hall resistance value for more than 24 h.

  • 5.
    Chung, S.
    et al.
    Department of Physics, Korea University.
    Kim, H. C.
    Lee, S.
    Liu, X.
    Furdyna, J. K.
    The effect of carrier density on magnetic anisotropy of the ferromagnetic semiconductor (Ga, Mn)As2009In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 149, no 41-42, p. 1739-1742Article in journal (Refereed)
    Abstract [en]

    Planar Hall effect (PHE) measurements are used to investigate magnetic anisotropy in two (Ga, Mn)As samples which differ by the hole concentration, but are otherwise identical. The difference in the hole density is controlled via modulation doping by Be. Angular dependence of PHE measured at 13 K reveals that the uniaxial easy axis in the sample with a lower hole concentration lies along the [110] direction, and along [over(1, ̄) 10] in the sample with higher doping. This difference in the orientation of uniaxial easy axes in the two samples demonstrates that the magnetization of GaMnAs can be manipulated just by varying the carrier density.

  • 6.
    Han, Shunhui
    et al.
    KTH, Superseded Departments, Physics.
    Andersson, Magnus
    KTH, Superseded Departments, Physics.
    Hegedüs, Zsolt
    Arrheniuslaboratoriet, Stockholms Universitet.
    Study of the upper critical magnetic field HC2 of YBA2CU3O7-DELTA compounds1992In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 82, no 5, p. 379-380Article in journal (Refereed)
    Abstract [en]

    Careful resistive measurements of the upper critical field H(c2) have been made on high quality polycrystalline YBa2Cu3O7-delta samples in magnetic fields up to 12 T. The data have been fitted on the form H(c2) infinity (T(c)-T)alpha to compare with theoretical models. A cusp is found in the H(c2) (T) curve for both of the samples. Different exponents-alpha are obtained depending on the temperature range used in the fitting procedure.

  • 7. Huang, L. M.
    et al.
    Silvearv, F.
    Araujo, Carlos Moyses
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Defect-induced strong ferromagnetism in Cr-doped In2O3 from first-principles theory2010In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 150, no 13-14, p. 663-665Article in journal (Refereed)
    Abstract [en]

    We demonstrate by means of first-principles calculations that the high Curie temperature observed in Cr-doped In2O3 is mediated by intrinsic p-type defects, namely In vacancies or O interstitials. Charge transfer from Cr 3d states to the hole states formed by these defects makes Cr ions in the mixed valence state, giving rise to a strong ferromagnetic coupling. Calculated formation energies of various defects also show that doping Cr in In2O3 could greatly lower the formation energies of p-type intrinsic defects even in oxygen-deficient growth conditions. These results advance our understanding of the underlying physics of diluted magnetic oxides.

  • 8. Isaeva, E. I.
    et al.
    Lichtenstein, A. I.
    Vekilov, Y. K.
    Smirnova, E. A.
    Abrikosov, I. A.
    Simak, S. I.
    Ahuja, Rajeev
    KTH, Superseded Departments, Materials Science and Engineering.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl2004In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 129, no 12, p. 809-814Article in journal (Refereed)
    Abstract [en]

    The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available experimental results from inelastic neutron scattering.

  • 9.
    Kadas, Krisztina
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Eriksson, O.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermo-physical properties of body-centered cubic iron-magnesium alloys under extreme conditions2011In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 151, no 3, p. 203-207Article in journal (Refereed)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron-magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi-Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C'). Magnesium alloying significantly increases C' of Fe, and bcc Fe-Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in detail. We show that the thermo-physical properties of a bcc Fe-Mg alloy with 5% Mg agree well with those of the Earth's inner core as provided by seismic observations. (C) 2010 Elsevier Ltd. All rights reserved.

  • 10.
    KARLSSON, Ulf O
    et al.
    KTH, School of Information and Communication Technology (ICT).
    FLODSTROM, SA
    ENGELHARDT, R
    GADEKE, W
    KOCH, EE
    INTRINSIC SURFACE-STATE ON BE(0001)1984In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 49, no 7, p. 711-714Article in journal (Refereed)
  • 11. Kaur, D.
    et al.
    Rao, K. V.
    KTH, Superseded Departments, Materials Science and Engineering.
    Microstructural and conductive properties of BaRuO3 thin films2003In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 128, no 9-10, p. 391-395Article in journal (Refereed)
    Abstract [en]

    We have brown conducting BaRuO3 films on (100) LaAlO3 substrate using pulsed laser deposition technique over temperature range varying from 500 to 775 T. The films are well textured and are c-axis oriented with an in-plane epitaxial relationship of <010><100>BaRuO(3)parallel to<110> LaAlO3. Atomic force microscopy observation shows that they consist of a fine arranged network of grains and have a mosaic microstructure. Surfaces with smooth terraces have been observed by Scanning Tunneling Microscopy. The resistivity of the films has been found to be a strong function of substrate temperature during film deposition. Both metallic and semiconducting behaviour has been observed in these films. Temperature-dependence resistivity measurement shows that the film has a metallic curve if it is deposited at 700degreesC or lower but it transfers to a semiconducting-metallic twofold curve if the deposition temperature is increased. This unique phenomenon, which is not observed in bulk, may provide new features useful in the fabrication of novel electronic devices.

  • 12. Kudrawiec, R.
    et al.
    Sek, G.
    Ryczko, K.
    Misiewicz, J.
    Sundgren, P.
    Asplund, C.
    Hammar, Mattias
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    The nature of optical transitions in Ga0.64In0.36As1-xNx/GaAs single quantum wells with low nitrogen content (x <= 0.008)2003In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 127, no 10-sep, p. 613-618Article in journal (Refereed)
    Abstract [en]

    Ga0.64In0.36As1-xNx/GaAs single quantum wells (SQWs) with low nitrogen content have been investigated by both photoluminescence (PL) and photoreflectance (PR) at low and room temperatures. A huge broadening of the PR features has been observed at low temperature and a decrease in this broadening with the temperature increase was detected. This effect and the nature of the optical transitions observed in absorption and emission can be explained using a model which assumes band gap variation due to different nitrogen nearest-neighbour environments (different configurations). In the framework of this model, the large Stokes shift observed for quantum wells (QWs) with smooth interfaces is explained as originating from the potential fluctuations of conduction band edge in the QW layer.

  • 13. Lee, H.
    et al.
    Chung, S.
    Department of Physics, Korea University.
    Lee, S.
    Liu, X.
    Furdyna, J. K.
    Temperature dependence of magnetization in GaMnAs film with critical strain2009In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 149, no 31-32, p. 1300-1303Article in journal (Refereed)
    Abstract [en]

    The temperature dependence of the magnetization properties of GaMnAs film, in which the strain was controlled to be in a critical condition by inserting a thin InGaAs layer, has been investigated by Hall measurements. The Hall resistance obtained with the magnetic fields perpendicular to the sample plane showed a slanted hysteresis, indicating the coexistence of in-plane and out-of-plane components of magnetization. The magnetic anisotropy fields of the sample were obtained from the angle dependence of the Hall resistance measurements. Using the magnetic anisotropy fields, the three-dimensional magnetic free energy diagrams were constructed for several temperatures. All energy diagrams show six energy minima along or near 〈 100 〉 directions, implying the possibility of magnetization within the plane and/or along out-of-plane directions in the system. Though the energy minima presented in the film plane (i.e., within the (001) plane) are deeper than those appeared along the out-of-plane direction (i.e., along the [001] direction) at 10 K, the situation is reversed as the temperature increases. This change of free energy density results in the temperature dependence of the magnetization directions in GaMnAs film with critical strain condition.

  • 14. Li, Chun-Xia
    et al.
    Luo, Hu-Bin
    Hu, Qing-Miao
    Yang, Rui
    Yin, Fu-Xing
    Umezawa, Osamu
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lattice parameters and relative stability of alpha '' phase in binary titanium alloys from first-principles calculations2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 159, p. 70-75Article in journal (Refereed)
    Abstract [en]

    The crystallographic structure and stability of the alpha" phase relative to the alpha and beta phases in Ti-x M (M=Ta, Nb, V, Mo) alloys are investigated by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. We show that, with increasing concentration of the alloying elements, the structure of the orthorhombic-alpha'' phase evolutes from the hcp-alpha to the bcc-beta phase, i.e., the lattice parameters b/a and c/a as well as the basal shuffle y decreases from those corresponding to the alpha phase to those of the beta phase. The compositional alpha/alpha" and alpha"/beta phase boundaries are determined by comparing the total energies of the phases. The predicted alpha/alpha" phase boundaries are about 10.2, 10.5, 11.5, 4.5 at% for Ti-V, Ti-Nb, Ti-Ta, and Ti-Mo, respectively, in reasonable agreement with experiments. The alpha"/beta phase boundaries are higher than the experimental values, possibly due to the absence of temperature effect in the first-principles calculations. Analyzing the electronic density of states, we propose that the stability of the alpha" phase is controlled by the compromise between the strength of the covalent and metallic bonds.

  • 15. Li, S.
    et al.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    The elastic and optical properties of the high-pressure hydrous phase delta-AlOOH2006In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 137, no 1-2, p. 101-106Article in journal (Refereed)
    Abstract [en]

    delta-AlOOH has recently been reported to be the least compressible hydrous phase known with a compressibility comparable to corundum and stishovite. It is predicted to be stable at the lower mantle conditions of the earth. By means of first principles methods, we have studied phase stability, electronic structure, elastic and optical properties of delta-AlOOH. Comparison between the elastic constants of delta-AlOOH and alpha-Al2O3 (corundum) shows that delta-AlOOH is as hard as corundum even though it contains 15% amount of water. In addition, delta-AlOOH has a calculated refractive index n similar to that of corundum.

  • 16.
    Li, Yunguo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Hussain, T.
    De Sarkar, Abid
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Hydrogen storage in polylithiated BC3 monolayer sheet2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 170, p. 39-43Article in journal (Refereed)
    Abstract [en]

    We perform a detailed study on the stability, electronic structure and hydrogen storage capacity of polylithiated (CLi3 functionalized) boron carbide (BC3) monolayer sheet using first-principles calculations. The binding of the CLi3 radical to the boron carbide (BC3) monolayer sheet is found to be large enough to ensure its uniform distribution without any clustering. The structural stability has been confirmed by molecular dynamics. Each lithium atom is able to accommodate 4 H2 molecules with an average binding energy of 0.21 eV, which is suitable for reversible H2 adsorption/desorption at ambient temperatures. The uptake of H2 is found to reach up to 9.83 wt% in polylithiated BC3 monolayer sheet.

  • 17. Lundin, U.
    et al.
    Sandalov, I.
    Eriksson, O.
    Johansson, Börje
    Modification of the standard model for the lanthanides2000In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 115, no 1, p. 7-12Article in journal (Refereed)
  • 18. Luo, W.
    et al.
    Yang, S. F.
    Wang, Z. C.
    Wang, Y.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Liu, J.
    Zou, G. T.
    Structural phase transitions in brookite-type TiO2 under high pressure2005In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 133, no 1, p. 49-53Article in journal (Refereed)
    Abstract [en]

    We have studied polycrystalline brookite TiO2 using energy-dispersive X-ray diffraction at pressures up to 27.8 GPa and derived an ambient-pressure bulk modulus of 255 GPa using Birch-Murnaghan's equations of state with a fixed value of 4 as its first derivative. The transition from brookite-type to baddeleyite-type was observed to start at 15.8 GPa and finished at 22.8 GPa. Upon decompression, the alpha-PbO2 structure appeared at 3.5 GPa and the baddeleyite-type structure remained down to 1.6 GPa. the lowest pressure in the present work.

  • 19. MAGNUSSON, KO
    et al.
    FLODSTROM, SA
    MARTENSSON, P
    NICHOLLS, JM
    KARLSSON, Ulf O
    KTH, School of Information and Communication Technology (ICT).
    ENGELHARDT, R
    KOCH, EE
    THE ELECTRONIC-STRUCTURE OF WURTZITE CDS STUDIES USING ANGLE-RESOLVED UV PHOTOELECTRON-SPECTROSCOPY1985In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 55, no 7, p. 643-647Article in journal (Refereed)
  • 20.
    Moskalenko, S. A.
    et al.
    Inst Appl Phys, Acad Str 5, MD-2028 Kishinev, Moldova..
    Khadzhi, P. , I
    Podlesny, I. , V
    Dumanov, E. , V
    Liberman, Michael A.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Zubac, I. A.
    Inst Appl Phys, Acad Str 5, MD-2028 Kishinev, Moldova..
    Metastable bound states of the interacting two-dimensional magnetoexcitons2018In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 283, p. 14-21Article in journal (Refereed)
    Abstract [en]

    The possible formation of two-dimensional (2D) magnetic biexcitons composed of two 2D magnetoexcitons with electrons and holes on the lowest Landau levels (LLLs) with opposite center-of-mass wave vectors (k)over-right-arrow and -(k)over-right-arrow and with antiparallel electric dipole moments perpendicular to the corresponding wave vectors was investigated. Two spinor structures of two electrons and of two holes were considered. In the singlet-singlet state the spins of two electrons as well as the effective spins of two holes create the combinations with the total spin S = 0 and its projection on the magnetic field S-z = 0. The triplet-triplet state corresponds to S = 1 and S-z = 0. Two orbital Gaussian variational wave functions depending on vertical bar(k)over-right-arrow vertical bar and describing the relative motion of two magnetoexcitons inside the molecule were used. Analytical calculations show that in the LLLs approximation the stable bound states of bimagnetoexcitons do not exist, but there is a metastable bound state with the orbital wave function, having the maximum on the in-plane ring for the triplet-triplet spin configuration. The metastable bound state has an energy activation barrier comparable with the magnetoexciton ionization potential and gives rise to the new luminescence band due to the metastable biexciton-para exciton conversion with the frequencies higher than those of the para magnetoexciton luminescence line.

  • 21. Moskalenko, S. A.
    et al.
    Podlesny, I. V.
    Dumanov, E. V.
    Liberman, Mikhail
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, S-10691 Stockholm, Sweden.
    Two-dimensional cavity polaritons under the influence of the perpendicular strong magnetic and electric fields. The gyrotropy effects2015In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 222, p. 58-64Article in journal (Refereed)
    Abstract [en]

    The properties of the two-dimensional cavity polaritons subjected to the action of a strong perpendicular magnetic and electric fields, giving rise to the Landau quantization (LQ) of the 2D electrons and holes accompanied by the Rashba spin-orbit coupling, by the Zeeman splitting and by the nonparabolicity of the heavy-hole dispersion law are investigated. We use the method proposed by Rashba (1960) [1] and the obtained results are based on the exact solutions for the eigenfunctions and for the eigenvalues of the Pauli-type Hamilonians with third order chirality terms and nonparabolic dispersion law for heavy-holes and with the first order chirality terms for electrons. The selection rules of the band-to-band optical quantum transitions as well as of the quantum transitions from the ground state of the crystal to the magnetoexciton states depend essentially on the numbers n(e) and n(h) of the LQ levels of the (e-h) pair forming the magnetoexciton. It is shown that the Rabi frequency Omega(R) of the polariton branches and the magnetoexciton oscillator strength f(osc), increase with the magnetic field strength B as Omega(R) similar to root B and f(osc) similar to B. The optical gyrotropy effects may be revealed changing the sign of the photon circular polarization at a given sign of the wave vector longitudinal projection k(z) or equivalently changing the sign of k(z) at the same selected circular polarization.

  • 22. Osorio-Guillen, J. M.
    et al.
    Simak, S. I.
    Wang, Y.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Ahuja, R.
    Bonding and elastic properties of superconducting MgB22002In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 123, no 07-jun, p. 257-262Article in journal (Refereed)
  • 23.
    Ramzan, M.
    et al.
    Uppsala Univ, Uppsala, Sweden .
    Lebegue, S.
    Nancy Univ, Vandoeuvre Les Nancy, France .
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Electronic and mechanical properties of Cr2GeC with hybrid functional and correlation effects2012In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 152, no 13, p. 1147-1149Article in journal (Refereed)
    Abstract [en]

    We present a computational study of the MAX phase material Cr2GeC to obtain its crystal and electronic structure using density functional theory with various exchange-correlation functionals. While the GGA and GGA+U methods are giving a reasonable description of the lattice parameters, the hybrid functional (HSE06) is found to give too large values. Then, on the basis of our GGA+U calculations, the antiferromagnetic ordering is found to be the ground state. Furthermore, we study the charge distribution between the constituent elements of this compound and find that the simple ionic model fails to describe it due to the complex nature of this material. Finally, we conclude that the treatment of the correlated electrons is important for the correct description of this material.

  • 24. Ramzan, M.
    et al.
    Li, Yunguo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Electronic structure, mechanical and optical properties of In 2O3 with hybrid density functional (HSE06)2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 172, p. 37-40Article in journal (Refereed)
    Abstract [en]

    In this study, the hybrid density correlation functional (HSE06) is used to explore the electronic structure and optical properties of In2O 3, on the basis of density functional theory (DFT). The calculated equilibrium lattice parameters, volume and bulk modulus of this compound, are comparable with the experimental results available in the literature. The bandgap of In2O3 has been a matter of debate in literatures. However, our calculated bandgap can bridge the gap between experiment and theory, and is in good agreement with the available experimental results. Furthermore, we calculate and analyze the optical and mechanical properties of this compound. We hope that our work will help to understand the correct electronic structure and optical properties of this compound.

  • 25. ROGELET, T
    et al.
    SODERHOLM, S
    QVARFORD, M
    SAINI, NL
    KARLSSON, Ulf O
    KTH, School of Information and Communication Technology (ICT).
    LINDAU, I
    FLODSTROM, SA
    ELECTRONIC-STRUCTURE OF NIO(1 0 0) WITH ADSORBED NA1993In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 85, no 7, p. 657-660Article in journal (Refereed)
    Abstract [en]

    Adsorption of Na on single crystals of NiO(1 0 0) at room temperature has been investigated via angle-resolved photoemission spectroscopy and measurements of work-function changes. The drastic changes in the valence band spectra upon Na deposition are assigned to a chemical reaction between Na and O where metallic Ni is left as by-product. At short deposition times, Na mainly acts as an inert electron donor, and at these coverages no dispersion is observed in the angle-resolved photoemission spectra which indicates that the electronic states are localized. The measurements were performed both for a polished and an in-situ cleaved NiO crystal.

  • 26.
    Srepusharawoot, P.
    et al.
    Khon Kaen Univ, Khon Kaen, Thailand.
    Luo, W.
    Uppsala Univ, Uppsala, Sweden .
    Bovornratanaraks, T.
    Chulalongkorn Univ, Bangkok, Thailand ; Commiss Higher Educ, Bangkok, Thailand .
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Pinsook, U.
    Chulalongkorn Univ, Bangkok, Thailand ; Commiss Higher Educ, Bangkok, Thailand.
    Evidence of a medium-range ordered phase and mechanical instabilities in strontium under high pressure2012In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 152, no 13, p. 1172-1175Article in journal (Refereed)
    Abstract [en]

    We provided the first theoretical evidence for a medium-range ordered phase in high pressure strontium from the first-principles calculations. At the absolute zero temperature, the enthalpy-pressure relation shows that the bcc and hcp are energetically more favorable than the other experimentally observed phases between 24 and 27 GPa. In the present work, we concentrate on the bcc phase because we found a link to a medium-range ordered phase. Our results reveal that the bcc phonon dispersion at the N and H points starts softening at around 24.1 GPa. The ab initio molecular dynamics at 300 K and 27 GPa showed that the bcc is quickly transformed into a lower energy structure with R3c symmetry and distorted basis. The simulated diffraction patterns showed that the R3c structure has only a single major peak at low angle. The R3c peak locates near the first peak of the bcc structure. This is the evidence of the so-called medium-range ordered phase. This structure is a strong candidate for the unsolved S-phase reported by experiments. (C) 2012 Elsevier Ltd. All rights reserved.

  • 27.
    Vaziri, Sam
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Smith, Anderson David
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Lupina, G.
    Dabrowski, J.
    Lippert, G.
    Mehr, W.
    Driussi, F.
    Venica, S.
    Di Lecce, V.
    Gnudi, A.
    Koenig, M.
    Ruhl, G.
    Belete, M.
    Lemme, M. C.
    Going ballistic: Graphene hot electron transistors2015In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 224, p. 64-75Article in journal (Refereed)
    Abstract [en]

    This paper reviews the experimental and theoretical state of the art in ballistic hot electron transistors that utilize two-dimensional base contacts made from graphene, i.e. graphene base transistors (GBTs). Early performance predictions that indicated potential for THz operation still hold true today, even with improved models that take non-idealities into account. Experimental results clearly demonstrate the basic functionality, with on/off current switching over several orders of magnitude, but further developments are required to exploit the full potential of the GBT device family. In particular, interfaces between graphene and semiconductors or dielectrics are far from perfect and thus limit experimental device integrity, reliability and performance.

  • 28. Vekilov, Y. K.
    et al.
    Isaev, E. I.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Diamagnetism in quasicrystals2005In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 133, no 7, p. 473-475Article in journal (Refereed)
  • 29. Yea, S.-y.
    et al.
    Chung, S. J.
    Son, H.
    Shin, D. Y.
    Lee, S.
    Liu, X.
    Furdyna, J. K.
    Effect of chemical etching on magnetic anisotropy of ferromagnetic GaMnAs films studied by planar Hall effect2008In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 147, no 7-8, p. 309-312Article in journal (Refereed)
    Abstract [en]

    We have investigated the effect of chemical etching on magnetic anisotropy of ferromagnetic GaMnAs film using the planar Hall effect (PHE). Different thicknesses were obtained on a single GaMnAs specimen by using different etching times on selected areas, and the PHE was then measured using the Hall bar configurations patterned on the area. Cubic and uniaxial anisotropy fields were obtained for the films by fitting the angular dependence of the PHE data to the Stoner-Wohlfarth model. The results exhibited a very systematic dependence on the etched thickness, demonstrating that the chemical etching process significantly affects the magnetic anisotropy of ferromagnetic GaMnAs films.

  • 30. Zeng, Yong
    et al.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Chen, Xiaoshuang
    Lu, Wei
    Effective dielectric constant of two-dimensional photonic crystals in optical bands2006In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 138, no 4, p. 205-210Article in journal (Refereed)
    Abstract [en]

    By using the Fourier expansion method, we have developed an approach to calculate the effective dielectric index of a two-dimensional photonic crystal. The approach is very general: it can take into account various Bravais lattice structure as well as arbitrary spatial variation of the dielectric index. It has been found that near a nondegenerate frequency w(n)(Gamma) at Gamma point, the transverse magnetic (TM) mode is ordinary, as it is independent of the propagation direction, whereas in general the transverse electric (TE) mode depends on the propagation direction, it is extraordinary. Therefore, a two-dimensional photonic crystal can always be described by an effective dielectric index for TM mode near the nondegenerate frequency w(n)(Gamma). However, the TE mode is much more complicated unless the lattice structure is highly symmetric. Moreover, a two-dimensional square photonic crystal has been identified as an effective birefringent crystal having two negative refractive indexes from the perspective of Snell's law.

  • 31.
    Zeng, Yong
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Chen, Xiaoshuang
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Lu, Wei
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Extended plane-wave-based transfer-matrix approach to simulating dispersive photonic crystals2006In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 139, no 7, p. 328-333Article in journal (Refereed)
    Abstract [en]

    It has been difficult to compute the band structures and transmission spectra for photonic crystals (PCs) with dispersive components included in the periodic units. Here we show that by using an extended plane-wave-based transfer-matrix method, we are able to formulate the problem for computing optical properties of dispersive PCs, including magnetic and left-handed PCs. This approach is very general, since it can treat PCs with arbitrary Bravais lattice composed of materials with arbitrary dielectric permittivities and magnetic permeabilities. Combined with the supercell method, this method can further simulate defective PCs such as PC-based waveguides and microcavities.

1 - 31 of 31
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