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Correlated Electronic Structure of Materials: Development and Application of Dynamical Mean Field Theory
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is dedicated to the development, implementation and application of a combination of Density Functional Theory and Dynamical Mean Field Theory. The resulting program is shown through several examples to be a powerful and flexible tool for calculating the electronic structure of strongly correlated materials. The main part of this work is focused on the development and implementation of three methods for solving the effective impurity model arising in the Dynamical Mean Field Theory: Hubbard-I approximation (HIA), Exact Diagonalization (ED), and Spin-Polarized T-matrix Fluctuation-exchange (SPTF). The Hubbard-I approximation is limited to systems where the hybridization between the 4f-orbitals and the rest of the material can be completely neglected, and can therefore not capture any Kondo physics. It has been used to study the atomic-like multiplet spectrum of the strongly localized 4f-electrons in the Lanthanide compounds YbInCu4, YbB12, Yb2Pd2Sn, YbPd2Sn, SmB6, SmSn3, and SmCo5. The calculated spectral properties are shown to be in excellent agreement with experimental direct and inverse photoemission data, clearly affirming the applicability of the Hubbard-I approximation for this class of systems if we are not focusing on Kondo physics. Full self-consistence in both self-energy and electron density is shown to be of key importance in the extraction of the magnetic properties of the hard permanent magnet SmCo5. The Exact Diagonalization solver is implemented as an extension of the Hubbard-I approximation. It takes into account a significant part of the hybridization between the correlated atom and the host through the use of a few effective bath orbitals. This approach has been applied to the long-standing problem of the electronic structure of NiO, CoO, FeO, and MnO. The resulting spectral densities are favorably compared to photoemission spectroscopy. Apart from predicting the correct spectral properties, the Exact Diagonalization solver also provides full access to the many-body density operator. This feature is used to make an in-depth investigation of the correlations in the electronic structure, and two measures of the quantum entanglement of the many-body ground-states are presented. It is shown that CoO possesses the most intricate entanglement properties, due to a competition between crystal field effects and Coulomb interaction, and such a mechanism likely carries over to several classes of correlated electron systems. The Exact Diagonalization solver has also been applied to the prototypical dilute magnetic semiconductor Mn doped GaAs, a material of great importance in the study of future spintronics applications. The problem of Fe impurities in Cs has been used to study the dependence of the spectral properties on the local environment. Finally, the Spin-polarized T-matrix Fluctuation-exchange solver has been implemented and applied to more delocalized electron systems where the effective impurity problem can be solved as a perturbation with respect to the strength of the local Coulomb interaction. This approach has been used to study the magnetic and spectral properties of the late transition metals, Fe, Co and Ni, and NiS.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 60 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 936
Keyword [en]
DFT, DMFT, correlation, entanglement
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-173300ISBN: 978-91-554-8376-0 (print)OAI: oai:DiVA.org:uu-173300DiVA: diva2:517622
Public defence
2012-06-07, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2012-05-16 Created: 2012-04-23 Last updated: 2012-08-01Bibliographically approved
List of papers
1. Multiplet effects in the electronic structure of intermediate-valence compounds
Open this publication in new window or tab >>Multiplet effects in the electronic structure of intermediate-valence compounds
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2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 16, 165104- p.Article in journal (Refereed) Published
Abstract [en]

We present an implementation of the Hubbard-I approximation based on the exact solution of the atomic many-body problem incorporated in a full-potential linear muffin-tin orbital method of density-functional theory. Comparison between calculated and measured x-ray photoemission spectra reveal a good agreement for intermediate valence systems in open crystal structures such as YbInCu4, SmB6, and YbB12. Spectral features of the unoccupied states of SmB6 are predicted.

Keyword
crystal structure, density functional theory, electronic structure, Hubbard model, indium compounds, linear muffin-tin orbital method, narrow band gap semiconductors, samarium compounds, X-ray photoelectron spectra, ytterbium compounds
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-129064 (URN)10.1103/PhysRevB.79.165104 (DOI)000265945200026 ()
Available from: 2010-08-06 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. High-resolution photoelectron spectroscopy study of Kondo metals: SmSn3 and Sm0.9La0.1Sn3
Open this publication in new window or tab >>High-resolution photoelectron spectroscopy study of Kondo metals: SmSn3 and Sm0.9La0.1Sn3
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2012 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 85, no 11, 115120- p.Article in journal (Refereed) Published
Abstract [en]

We performed a high-resolution photoelectron spectroscopy study on the Kondo metals SmSn3 and Sm0.9La0.1Sn3. The experimental results are compared with calculations of density of state performed within the local density approximation plus the dynamical mean-field theory. The theory is found to reproduce the experimental valence-band spectra well. In both SmSn3 and Sm0.9La0.1Sn3 the bulk Sm valence is nearly trivalent, with a small fraction of divalent component. Resonant photoelectron spectroscopy indicates a decrease in the Kondo effect in the diluted system Sm0.9La0.1Sn3.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173287 (URN)10.1103/PhysRevB.85.115120 (DOI)000301916100002 ()
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2017-12-07Bibliographically approved
3. Study of the electronic structures on Yb$_2$Pd$_2$Sn and YbPd$_2$Sn by photoelectron and x-ray emission spectroscopies
Open this publication in new window or tab >>Study of the electronic structures on Yb$_2$Pd$_2$Sn and YbPd$_2$Sn by photoelectron and x-ray emission spectroscopies
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173292 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2012-08-01
4. Charge self-consistent dynamical mean-field theory based on the full-potential linear muffin-tin orbital method: Methodology and applications
Open this publication in new window or tab >>Charge self-consistent dynamical mean-field theory based on the full-potential linear muffin-tin orbital method: Methodology and applications
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2012 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, 295-302 p.Article in journal (Refereed) Published
Abstract [en]

Full charge self-consistence (CSC) over the electron density has been implemented into the local density approximation plus dynamical mean-field theory (LDA + DMFT) scheme based on a full-potential linear muffin-tin orbital method (FP-LMTO). Computational details on the construction of the electron density from the density matrix are provided. The method is tested on the prototypical charge-transfer insulator NiO using a simple static Hartree-Fock approximation as impurity solver. The spectral and ground state properties of bcc Fe are then addressed, by means of the spin-polarized T-matrix fluctuation exchange solver (SPTF). Finally the permanent magnet SmCo5 is studied using multiple impurity solvers, SPTF and Hubbard I, as the strength of the local Coulomb interaction on the Sm and Co sites are drastically different. The developed CSC-DMFT method is shown to in general improve on materials properties like magnetic moments, electronic structure and the materials density.

Keyword
Dynamical mean-field theory, Correlated materials, NiO, Fe, SmCo5
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-171397 (URN)10.1016/j.commatsci.2011.11.032 (DOI)000300728600039 ()
Available from: 2012-03-20 Created: 2012-03-19 Last updated: 2017-12-07Bibliographically approved
5. Electronic entanglement in late transition metal oxides
Open this publication in new window or tab >>Electronic entanglement in late transition metal oxides
2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 18, 186401- p.Article in journal (Refereed) Published
Abstract [en]

We present a study of the entanglement in the electronic structure of the late transition metal monoxides-MnO, FeO, CoO, and NiO-obtained by means of density-functional theory in the local density approximation combined with dynamical mean-field theory. The impurity problem is solved through exact diagonalization, which grants full access to the thermally mixed many-body ground state density operator. The quality of the electronic structure is affirmed through a direct comparison between the calculated electronic excitation spectrum and photoemission experiments. Our treatment allows for a quantitative investigation of the entanglement in the electronic structure. Two main sources of entanglement are explicitly resolved through the use of a fidelity based geometrical entanglement measure, and additional information is gained from a complementary entropic entanglement measure. We show that the interplay of crystal field effects and Coulomb interaction causes the entanglement in CoO to take a particularly intricate form.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173295 (URN)10.1103/PhysRevLett.109.186401 (DOI)000310434400021 ()
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2017-12-07Bibliographically approved
6. Spectral properties of Mn doped GaAs: experiment and correlated electronic structure theory
Open this publication in new window or tab >>Spectral properties of Mn doped GaAs: experiment and correlated electronic structure theory
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173293 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2012-08-01
7. Correlated electronic structure of Fe in Cs
Open this publication in new window or tab >>Correlated electronic structure of Fe in Cs
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173294 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2012-08-01
8. An LDA+DMFT study of the orbital magnetism and total energy properties of the late transition metals: conserving and non-conserving approximations
Open this publication in new window or tab >>An LDA+DMFT study of the orbital magnetism and total energy properties of the late transition metals: conserving and non-conserving approximations
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173298 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2012-08-01
9. A charge self-consistent LDA+DMFT study of the spectral properties of NiS
Open this publication in new window or tab >>A charge self-consistent LDA+DMFT study of the spectral properties of NiS
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-173296 (URN)
Available from: 2012-04-23 Created: 2012-04-23 Last updated: 2012-08-01

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