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Diese Dissertation wurde selbstständig, ohne unerlaubte Hilfe erarbeitet. München, am 20.12.2007

Diese Dissertation wurde selbstständig, ohne unerlaubte Hilfe erarbeitet. München, am 20.12.2007 Minimize

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The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2012-06-25

Source:

http://edoc.ub.uni-muenchen.de/8711/1/Chadov_Stanislav.pdf

http://edoc.ub.uni-muenchen.de/8711/1/Chadov_Stanislav.pdf Minimize

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text

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en

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Metadata may be used without restrictions as long as the oai identifier remains attached to it.

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Title:

Electron correlations in Co2Mn1−xFexSi Heusler compounds.

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Abstract. This study presents the effect of local electronic correlations on the Heusler compounds Co2Mn1−xFexSi as a function of the concentration x. The analysis has been performed by means of first-principles band-structure calculations based on the local approximation to spin-density functional theory (LSDA). Correlation effects are treated ...

Abstract. This study presents the effect of local electronic correlations on the Heusler compounds Co2Mn1−xFexSi as a function of the concentration x. The analysis has been performed by means of first-principles band-structure calculations based on the local approximation to spin-density functional theory (LSDA). Correlation effects are treated in terms of the Dynamical Mean-Field Theory (DMFT) and the LSDA+U approach. The formalism is implemented within the Korringa-Kohn-Rostoker (KKR) Green’s function method. In good agreement with the available experimental data the magnetic and spectroscopic properties of the compound are explained in terms of strong electronic correlations. In addition the correlation effects have been analysed separately with respect to their static or dynamical origin. To achieve a quantitative description of the electronic structure of Co2Mn1−xFexSi both static and dynamic correlations must be treated on equal footing. Minimize

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The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2012-11-26

Source:

http://arxiv.org/pdf/0811.4625v1.pdf

http://arxiv.org/pdf/0811.4625v1.pdf Minimize

Document Type:

text

Language:

en

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Title:

Application of Many-Body Perturbation Theory to the Description of Correlated Metals

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An efficient computational LSDA+DMFT toolbox for the description of correlated materials has been established. The method developed in this work provides an appropriate description of 3d-transition metal correlated bulk systems, concerning their ground-state properties (magnetic moments, total energies) as well as the high- and low-energy spectr...

An efficient computational LSDA+DMFT toolbox for the description of correlated materials has been established. The method developed in this work provides an appropriate description of 3d-transition metal correlated bulk systems, concerning their ground-state properties (magnetic moments, total energies) as well as the high- and low-energy spectroscopies (valence-band angular-resolved photoemission, Fano-effect, optical and magneto-optical properties). The incorporation of the perturbational impurity solvers within the spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) Green’s function method gives rise to a fully self-consistent procedure with respect both to the DFT (charge) and the DMFT (localized dynamical self-energy) self-consistency requirements. Thus, the solution of the many-electron problem can be achieved with a high precision. In turn this opens a possibility to investigate very delicate properties, as the orbital magnetic moments of 3d-transition metals. To develop a relatively fast and accurate approach for the low-energy spectroscopies, the DMFT was implemented within the wave function formalism in the framework of the Linearized Muffin-Tin Orbitals method (LMTO). Calculations are performed in a one-shot run, that does not allow to get the charge-self-consistent solution. In such a way all effects of the localized correlations are encapsulated in the Green’s function constructed as a resolvent to the LMTO one-particle Hamiltonian and accounting for the corresponding self-energy via the Dyson equation. The LMTO+DMFT scheme gives in comparison to a plain LSDA a significantly improved description of the magneto-optics in the 3d-transition metals, half-metallic Heusler ferromagnet NiMnSb, as well as for the heavy-fermion US compound. Minimize

Publisher:

Ludwig-Maximilians-Universität München

Year of Publication:

2007-12-20

Document Type:

Dissertation ; NonPeerReviewed

Subjects:

Fakultät für Chemie und Pharmazie

Fakultät für Chemie und Pharmazie Minimize

DDC:

530 Physics *(computed)*

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http://edoc.ub.uni-muenchen.de/8711/

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Title:

The role of correlations in the high-pressure phase of FeSe

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We present a systematic study of the high-pressure FeSe phase performed by means of the first-principle electronic structure calculations. Basing on available experimental information about the unit cell geometry we calculate the band structure and characterize the related properties during their pressure driven evolution. The electronic structu...

We present a systematic study of the high-pressure FeSe phase performed by means of the first-principle electronic structure calculations. Basing on available experimental information about the unit cell geometry we calculate the band structure and characterize the related properties during their pressure driven evolution. The electronic structure including the hybrid functional B3LYP or the Hubbard parameter U for the iron d states lead to the correct semiconducting ground state for the hexagonal stoichiometric FeSe within the broad pressure range (up to 30 GPa). Minimize

Year of Publication:

2010-11-03

Document Type:

text

Subjects:

Condensed Matter - Superconductivity ; Condensed Matter - Strongly Correlated Electrons

Condensed Matter - Superconductivity ; Condensed Matter - Strongly Correlated Electrons Minimize

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Title:

Topological insulators and thermoelectric materials

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Topological insulators (TIs) are a new quantum state of matter which have gapless surface states inside the bulk energy gap. Starting with the discovery of two dimensional TIs, the HgTe-based quantum wells, many new topological materials have been theoretically predicted and experimentally observed. Currently known TI materials can possibly be c...

Topological insulators (TIs) are a new quantum state of matter which have gapless surface states inside the bulk energy gap. Starting with the discovery of two dimensional TIs, the HgTe-based quantum wells, many new topological materials have been theoretically predicted and experimentally observed. Currently known TI materials can possibly be classified into two families, the HgTe family and the Bi2Se family. The signatures found in the electronic structure of a TI also cause these materials to be excellent thermoelectric materials. On the other hand, excellent thermoelectric materials can be also topologically trivial. Here we present a short introduction to topological insulators and thermoelectrics, and give examples of compound classes were both good thermoelectric properties and topological insulators can be found. ; Comment: Phys. Status Solidi RRL, accepted Minimize

Year of Publication:

2012-09-26

Document Type:

text

Subjects:

Condensed Matter - Materials Science

Condensed Matter - Materials Science Minimize

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Title:

Disorder-induced cubic phase in Fe$_2$-based Heusler alloys

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Based on first-principles electronic structure calculations, we analyze the chemical and magnetic mechanisms stabilizing the cubic phase in Fe$_2$-based Heusler materials, which were previously predicted to be tetragonal when being chemically ordered. In agreement with recent experimental data, we found that these compounds crystallize within th...

Based on first-principles electronic structure calculations, we analyze the chemical and magnetic mechanisms stabilizing the cubic phase in Fe$_2$-based Heusler materials, which were previously predicted to be tetragonal when being chemically ordered. In agreement with recent experimental data, we found that these compounds crystallize within the so-called "inverted" cubic Heusler structure perturbed by a certain portion of the intrinsic chemical disorder. Understanding these mechanisms is a necessary step to guide towards the successful future synthesis of the stable Fe$_2$-based tetragonal phases, which are very promising candidates for the fabrication of rare-earth-free permanent magnets. Minimize

Year of Publication:

2013-02-04

Document Type:

text

Subjects:

Condensed Matter - Materials Science

Condensed Matter - Materials Science Minimize

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Title:

Topological phase transitions in bulk

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We consider the analogy between the topological phase transition which occurs as a function of spatial coordinate on a surface of a non-trivial insulator, and the one which occurs in the bulk due to the change of internal parameters (such as crystal field and spin-orbit coupling). In both cases the system exhibits a Dirac cone, which is the univ...

We consider the analogy between the topological phase transition which occurs as a function of spatial coordinate on a surface of a non-trivial insulator, and the one which occurs in the bulk due to the change of internal parameters (such as crystal field and spin-orbit coupling). In both cases the system exhibits a Dirac cone, which is the universal manifestation of topological phase transition, independently on the type of driving parameters. In particular, this leads to a simple way of determining the topological class based solely on the bulk information even for the systems with translational symmetry broken by atomic disorder or by strong electron correlations. Here we demonstrate this on example of the zinc-blende related semiconductors by means of the {\it ab-initio} fully-relativistic band structure calculations involving the coherent potential approximation (CPA) technique. ; Comment: Phys. Status Solidi RRL, DOI 10.1002/pssr.2012064xx (2012), submitted Minimize

Year of Publication:

2012-09-27

Document Type:

text

Subjects:

Condensed Matter - Materials Science

Condensed Matter - Materials Science Minimize

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Title:

Guidelines for understanding cubic manganese-rich Heusler compounds

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Manganese-rich Heusler compounds are attracting much interest in the context of spin transfer torque and rare-earth free hard magnets. Here we give a comprehensive overview of the magnetic properties of non-centrosymmetric cubic Mn$_2$-based Heusler materials, which are characterized by an antiparallel coupling of magnetic moments on Mn atoms. S...

Manganese-rich Heusler compounds are attracting much interest in the context of spin transfer torque and rare-earth free hard magnets. Here we give a comprehensive overview of the magnetic properties of non-centrosymmetric cubic Mn$_2$-based Heusler materials, which are characterized by an antiparallel coupling of magnetic moments on Mn atoms. Such a ferrimagnetic order leads to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures. In terms of the band structure calculations, we explain the formation of this magnetic order and the Curie temperatures. This overview is intended to establish guidelines for a basic understanding of magnetism in Mn2 -based Heusler compounds. Minimize

Year of Publication:

2014-09-23

Document Type:

text

Subjects:

Condensed Matter - Materials Science

Condensed Matter - Materials Science Minimize

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Title:

The efficient spin injector scheme based on Heusler materials

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We present the rational design scheme intended to provide the stable high spin-polarization at the interfaces of the magneto-resistive junctions by fulfilling the criteria of structural and chemical compatibilities at the interface. This can be realized by joining the semiconducting and half-metallic Heusler materials with similar structures. Th...

We present the rational design scheme intended to provide the stable high spin-polarization at the interfaces of the magneto-resistive junctions by fulfilling the criteria of structural and chemical compatibilities at the interface. This can be realized by joining the semiconducting and half-metallic Heusler materials with similar structures. The present first-principal calculations verify that interface remains half-metallic if the nearest interface layers effectively form a stable Heusler material with the properties intermediate between the surrounding bulk parts. This leads to a simple rule for selecting the proper combinations. Minimize

Year of Publication:

2011-03-30

Document Type:

text

Subjects:

Condensed Matter - Materials Science

Condensed Matter - Materials Science Minimize

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Title:

Topological phase transition induced by random substitution

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The transition from topologically nontrivial to a trivial state is studied by first-principles calculations on bulk zinc-blende type (Hg$_{1-x}$Zn$_x$)(Te$_{1-x}$S$_x$) disordered alloy series. The random chemical disorder was treated by means of the Coherent Potential Approximation. We found that although the phase transition occurs at the stro...

The transition from topologically nontrivial to a trivial state is studied by first-principles calculations on bulk zinc-blende type (Hg$_{1-x}$Zn$_x$)(Te$_{1-x}$S$_x$) disordered alloy series. The random chemical disorder was treated by means of the Coherent Potential Approximation. We found that although the phase transition occurs at the strongest disorder regime (${x\approx 0.5}$), it is still manifested by well-defined Bloch states forming a clear Dirac cone at the Fermi energy of the bulk disordered material. The computed residual resistivity tensor confirm the topologically-nontrivial state of the HgTe-rich (${x<0.5}$), and the trivial state of the ZnS-rich alloy series (${x>0.5}$) by exhibiting the quantized behavior of the off-diagonal spin-projected component, independently on the concentration $x$. Minimize

Year of Publication:

2012-07-14

Document Type:

text

Subjects:

Condensed Matter - Materials Science

Condensed Matter - Materials Science Minimize

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