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Theory of L-edge spectroscopy of strongly correlated systems
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. National University of Singapore, Department of Mechanical Engineering.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Heidelberg University, Institute for Theoretical Physics.
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, article id 245131Article in journal (Refereed) Published
Abstract [en]

X-ray absorption spectroscopy measured at the L edge of transition metals (TMs) is a powerful element-selective tool providing direct information about the correlation effects in the 3d states. The theoretical modeling of the 2p→3d excitation processes remains to be challenging for contemporary ab initio electronic structure techniques, due to strong core-hole and multiplet effects influencing the spectra. In this work, we present a realization of the method combining the density-functional theory with multiplet ligand field theory, proposed in Haverkort et al. [Phys. Rev. B 85, 165113 (2012)]. In this approach, a single-impurity Anderson model (SIAM) is constructed, with almost all parameters obtained from first principles, and then solved to obtain the spectra. In our implementation, we adopt the language of the dynamical mean-field theory and utilize the local density of states and the hybridization function, projected onto TM 3d states, in order to construct the SIAM. The developed computational scheme is applied to calculate the L-edge spectra for several TM monoxides. A very good agreement between the theory and experiment is found for all studied systems. The effect of core-hole relaxation, hybridization discretization, possible extensions of the method as well as its limitations are discussed.

Place, publisher, year, edition, pages
2017. Vol. 96, no 24, article id 245131
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-339767DOI: 10.1103/PhysRevB.96.245131ISI: 000418573600012OAI: oai:DiVA.org:uu-339767DiVA, id: diva2:1179980
Funder
Knut and Alice Wallenberg Foundation, 2013.0020; 2012.0031Carl Tryggers foundation Available from: 2018-02-02 Created: 2018-02-02 Last updated: 2018-10-10Bibliographically approved
In thesis
1. Theoretical and Computational Studies of Strongly Correlated Electron Systems: Dynamical Mean Field Theory, X-ray Absorption Spectroscopy and Analytical Continuation
Open this publication in new window or tab >>Theoretical and Computational Studies of Strongly Correlated Electron Systems: Dynamical Mean Field Theory, X-ray Absorption Spectroscopy and Analytical Continuation
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis encompasses theoretical and computational studies of strongly correlated elec-tron systems. Understanding how electrons in solids interact with each other is of great im-portance for future technology and other applications. From a fundamental point of view, the Coulomb interaction in a solid leads to a very challenging many-body problem, encapsulating many physical phenomena, e.g. magnetism. Treating this interaction, with a focus on local contributions, is the subject of this thesis. Both models and materials have been investigated, to obtain insight on the mechanisms determining the macroscopic properties of matter. This thesis is divided in four parts, each corresponding to a different project or topic.

In the first project a many body method called dynamical mean field theory (DMFT) is used to study the paramagnetic phase of the Hubbard model. A stochastic version of the exact di-agonalization technique is developed for solving the effective impurity model arising in DMFT and generating real frequency spectral functions. In the next project, by combining density functional theory (DFT) with a static solution of the DMFT equations (DFT+U), magnetic ex-change interactions in transition metal oxides (TMOs) are investigated. The spin dependence of the functional is shown to be important for mapping magnetic excitations form the quantum mechanical system to a classical model.

The next topic in this thesis concerns the x-ray absorption spectroscopy of TMOs. Spectral functions, in good agreement with experimental data, are calculated by combining DFT with multiplet ligand field theory (MLFT). The effects of the presence of a core-hole are studied in detail for NiO, as well as double counting issues related to higher order terms of the multiple ex-pansion of the Coulomb interaction. A strained induced linearly polarized spectrum is obtained for CaTiO3. Lastly, charge disproportionation is seen in Mo doped LaFeO3.

Finally, a critical step in DMFT, called analytical continuation, to obtain physical observ-ables of interest is investigated. Analytical continuation means a transformation of a function in the complex plane. Several methods for performing this transformation are explained, and in particular steps for improving the robustness and accuracy of the Padé approximant method are described.

Place, publisher, year, edition, pages
Uppala: Acta Universitatis Upsaliensis, 2018. p. 112
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1729
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-362834 (URN)978-91-513-0471-7 (ISBN)
Public defence
2018-11-30, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Note

the opponents university is University of Bremen

Available from: 2018-11-09 Created: 2018-10-10 Last updated: 2018-11-19

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Lüder, JohannSchött, JohanBrena, BarbaraThunström, PatrikEriksson, OlleSanyal, BiplabDi Marco, IgorKvashnin, Yaroslav

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