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Multipolar and orbital ordering in ferro-pnictides
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.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The stability of different solutions corresponding to various arrangement of magnetic rank-4 multipoles are evaluated for the ferro-pnictides LaOFeAs, BaFe2As2 and CaFe2As2 compounds. For LaOFeAs, the ground-state solution is identified with a combination of large w4120 and w4120 multipole tensors of the magnetization density which integrates to the correct value of experimental moment. The same procedure is applied to BaFe2As2 and CaFe2 As2 where the lowest energy solution corresponds again to a combination of w4120 and w4120 multipoles, but with a magnetic moment lower than the experimental value. However, for these compounds, our calculated moment constitutes a significant improvement over previous ab-initio calculations that largely overestimate the Fe moment. Moreover for BaFe2As2 and CaFe2As2 , in the total energy curves as function of constrained spin moment, we identify a local minima close to the experimental moment.

Keyword [en]
High temperature superconductivity, correlated electrons, electronic structure calculations
National Category
Condensed Matter Physics
Research subject
Physics of Matter
Identifiers
URN: urn:nbn:se:uu:diva-132066OAI: oai:DiVA.org:uu-132066DiVA: diva2:356797
Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2012-04-03
In thesis
1. Multipoles in Correlated Electron Materials
Open this publication in new window or tab >>Multipoles in Correlated Electron Materials
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electronic structure calculations constitute a valuable tool to predict the properties of materials. In this study we propose an efficient scheme to study correlated electron systems with essentially only one free parameter, the screening length of the Coulomb potential. A general reformulation of the exchange energy of the correlated electron shell is combined with this method in order to analyze the calculations. The results are interpreted in terms of different polarization channels, due to different multipoles. The method is applied to various actinide compounds, in order to increase the understanding of the complicate behaviour of 5f electrons in these systems. We studied the non-magnetic phase of δ-Pu, where the spin polarization is taken over by a spin-orbit-like term that does not break the time reversal symmetry. We also find that a non-trivial high multipole of the magnetization density, the triakontadipole, constitutes the ordering parameter in the mysterious hidden order phase of the heavy-fermion superconductor URu2Si2. This type of multipolar ordering is also found to play an essential role in the hexagonal-based superconductors UPd2Al3,  UNi2Al3 and UPt3 and in the dioxide insulators UO2, NpO2 and PuO2. The triakontadipole moments are also present in all magnetic actinides we considered, except for Cm. These results led us to formulate a new set of rules for the ground state of a system, that are valid in presence of strong spin-orbit coupling interaction instead of those of Hund; the Katt's rules. Finally, we applied our method to a new class of high-Tc superconductors, the Fe-pnictides, where the Fe 3d electrons are moderately correlated. In these materials we obtain the stabilization of a low spin moment solution, in agreement with experiment, over a large moment solution, due to the gain in exchange energy in the formation of large multipoles of the spin magnetization density.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 775
Keyword
correlated electrons, magnetic ordering, multipoles, actinides, hidden order, high temperature superconductors, Fe pnictides, electronic structure calculations
National Category
Condensed Matter Physics Condensed Matter Physics Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-132068 (URN)978-91-554-7917-6 (ISBN)
Public defence
2010-11-26, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 705Available from: 2010-11-04 Created: 2010-10-13 Last updated: 2011-03-21Bibliographically approved

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Grånäs, OscarNordström, Lars

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