| 1. |
- Rusydi, A., et al.
(författare)
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Metal-insulator transition in manganites: Changes in optical conductivity up to 22 eV
- 2008
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 78:12, s. 125110 (art. no.)-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic response of doped manganites at the transition from the paramagnetic insulating to the ferromagnetic metallic state in La(1-x)Ca(x)MnO(3) for x=0.3 and 0.2 was investigated by dc conductivity, ellipsometry, and vacuum ultraviolet reflectance for energies between 0 and 22 eV. A stabilized Kramers-Kronig transformation yields the optical conductivity and reveals changes in the optical spectral weight up to 22 eV at the metal-to-insulator transition. In the observed energy range, the spectral weight is conserved within 0.3%. The redistribution of spectral weight in this surprisingly broad energy range has important ramifications for the effective low-energy physics. We discuss the importance of the charge-transfer, Coulomb on-site, Jahn-Teller, and long-range Coulomb screening effects to the electronic structure.
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| 2. |
- Sanchez-Barriga, J., et al.
(författare)
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Strength of Correlation Effects in the Electronic Structure of Iron
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:26, s. 267203-
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Tidskriftsartikel (refereegranskat)abstract
- The strength of electronic correlation effects in the spin-dependent electronic structure of ferromagnetic bcc Fe(110) has been investigated by means of spin and angle-resolved photoemission spectroscopy. The experimental results are compared to theoretical calculations within the three-body scattering approximation and within the dynamical mean-field theory, together with one-step model calculations of the photoemission process. This comparison indicates that the present state of the art many-body calculations, although improving the description of correlation effects in Fe, give too small mass renormalizations and scattering rates thus demanding more refined many-body theories including nonlocal fluctuations.
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| 3. |
- Boukhvalov, D. W., et al.
(författare)
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Electronic structure of a Mn-12 molecular magnet : Theory and experiment
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:1, s. 014419-
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Tidskriftsartikel (refereegranskat)abstract
- We used site-selective and element-specific resonant inelastic x-ray scattering (RIXS) to study the electronic structure and the electron interaction effects in the molecular magnet [Mn12O12(CH3COO)(16)(H2O)(4)]center dot 2CH(3)COOH center dot 4H(2)O, and compared the experimental data with the results of local spin density approximation +U electron structure calculations which include the on-site Coulomb interactions. We found a good agreement between theory and experiment for the Coulomb repulsion parameter U = 4 eV. In particular, the p-d band separation of 1.8 eV has been found from the RIXS spectra, which is in accordance with the calculations. Similarly, the positions of the peaks in the XPS spectra agree with the calculated densities of p and d states. Using the results of the electronic structure calculations, we determined the intramolecular exchange parameters, and used them for diagonalization of the Mn-12 spin Hamiltonian. The calculated exchanges gave the correct ground state with the total spin S = 10.
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| 4. |
- Isaev, E. I., et al.
(författare)
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Phonon related properties of transition metals, their carbides, and nitrides : A first-principles study
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:12
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Forskningsöversikt (refereegranskat)abstract
- Lattice dynamics of body-centered cubic (bcc) V-b-VIb group transition metals (TM), and B1-type monocarbides and mononitrides of IIIb-VIb transition metals are studied by means of first-principles density functional perturbation theory, ultra soft pseudopotentials, and generalized gradient approximation to the exchange-correlation functional. Ground state parameters of transition metals and their compounds are correctly reproduced with the generated ultrasoft pseudopotentials. The calculated phonon spectra of the bcc metals are in excellent agreement with results of inelastic neutron scattering experiments. We show that the superconductivity of transition metal carbides (TMC) and transition metal nitrides (TMN) is related to peculiarities of the phonon spectra, and the anomalies of the spectra are connected to the number of valence electrons in crystals. The calculated electron-phonon interaction constants for TM, TMC, and TMN are in excellent agreement with experimentally determined values. Phonon spectra for a number of monocarbides and mononitrides of transition metals within the cubic NaCl- and hexagonal WC-type structures are predicted. Ideal stoichiometric B1 crystals of ScC, YC, and VC are predicted to be dynamically stable and superconducting materials. We also conclude that YN is a semiconductor.
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| 5. |
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| 6. |
- Di Marco, Igor, et al.
(författare)
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gamma-Mn at the border between weak and strong correlations
- 2009
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 72:4, s. 473-478
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the role of magnetic fluctuations in the spectral properties of paramagnetic gamma-Mn. Two methods are employed. The Local Density Approximation plus Dynamical Mean-Field Theory together with the numerically exact quantum Monte-Carlo solver is used as a reference for the spectral properties. Then the same scheme is used with the computationally less demanding perturbative spin-polarized fluctuation-exchange solver in combination with the Disordered Local Moment approach, and photoemission spectra are calculated within the one-step model. It is shown that the formation of local magnetic moments in gamma-Mn is very sensitive to the value of Hund's exchange parameter. Comparison with the experimental photoemission spectra demonstrates that gamma-Mn is a strongly correlated system, with the Hubbard band formation, which cannot be described by the perturbative approach. However, minor change of parameters would transform it into a weakly correlated system.
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| 7. |
- Grechnev, Alexei, et al.
(författare)
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Theory of bulk and surface quasiparticle spectra for Fe, Co, and Ni
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:3, s. 035107-
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Tidskriftsartikel (refereegranskat)abstract
- The correlated quasiparticle band structure of iron, cobalt, and nickel is investigated within the dynamical mean-field theory formalism using the recently developed full-potential linear-muffin-tin-orbital-based local-density approximation plus dynamical mean-field theory (LDA+DMFT) code. Detailed analysis of the calculated electron self-energy, density of states, and the spectral density is presented for these metals. It has been found that all these elements show strong correlation effects for majority-spin electrons, such as strong damping of quasiparticles and formation of a satellite state below the bottom of d bands. In particular, our work clearly predicts the existence of a photoemission satellite for bcc iron. The LDA+DMFT data for fcc nickel and cobalt (111) surfaces and bcc iron (001) surface are also presented. The electron self-energy is found to depend strongly on the number of nearest neighbors, and it practically reaches the bulk value already in the second layer from the surface. The dependence of correlation effects on the dimensionality of the problem is also discussed.
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| 8. |
- Lebègue, Sebastien, et al.
(författare)
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Multiplet effects in the electronic structure of heavy rare-earth metals
- 2006
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Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 18, s. 6329-
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Tidskriftsartikel (refereegranskat)abstract
- The spectroscopic properties of elemental terbium, dysprosium, holmium, and erbium are investigated using first-principles calculations taking into account intra-atomic correlation effects. In order to describe the strongly localized f electrons together with the conduction bands, we have used the multiband Hubbard-I approximation to reproduce the multiplet features present in the experimental spectra. A comparison with available experimental data is made and the overall agreement is found to be good.
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| 9. |
- Lebègue, Sebastien, et al.
(författare)
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Multiplet effects in the electronic structure of light rare-earth metals
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:4, s. 045114-
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Tidskriftsartikel (refereegranskat)abstract
- The excited-state properties of the light rare-earth elemental metals praseodymium, neodymium, and samarium are studied within the Hubbard-I formalism. This method describes the multiplets of the rare-earth f shell by an exact diagonalization of the two-body part of the Hamiltonian. Subsequently, the rare-earth ion is embedded in the solid environment by incorporation of the atomic self-energy into a solid Green's function, which is calculated using the local density approximation to density functional theory. After describing the method briefly, a systematic comparison with available photoemission experiments is made, and it is found that all main structures of the experimental spectra are reproduced by the approach, with the exception of the features immediately below the Fermi level which are interpreted as a mark of a mechanism different from an atomiclike multiplet transition.
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| 10. |
- Lebegue, Sebastien, et al.
(författare)
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Electronic structure and spectroscopic properties of thulium monochalcogenides
- 2005
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 72:24, s. 245102-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the thulium monochalcogenides TmS, TmSe, and TmTe is studied with several theoretical approaches. The total energy is evaluated with the self-interaction corrected local-spin density approximation, whereby the Tm ions are described with either twelve or thirteen localized f electrons with the remaining electrons forming bands. The comparisons of these two scenarios reveal the valency shift of the Tm ion through the series. The spectral functions of TmX compounds are calculated including multiplet effects, and they are compared to experimental x-ray photoemission spectra. The basic tool is the Hubbard-I approximation in which the embedding of an isolated f(n) ion in a solid is performed by modifying the crystal Hamiltonian as obtained from the local-density approximation with the atomic self-energy of the ion. The parameters of the model are obtained from the self-consistent band structure calculation. The agreement with experiment is excellent, reproducing all significant multiplet structures.
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