First-principles investigation of inelastic magnetic excitations in nanostructures deposited on surfaces
| Autor: | Schweflinghaus, Benedikt Johannes |
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| Přispěvatelé: | Lounis, Samir, Honerkamp, Carsten |
| Jazyk: | angličtina |
| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | Jülich : Forschungszentrum Jülich GmbH, Zentralbibliothek, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien 117, v, 204 Seiten : Illustrationen, Diagramme (2016). = Dissertation, RWTH Aachen, 2015 Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / Key Technologies 117, V, 204 S. (2016). = RWTH Aachen, Diss., 2015 |
| Popis: | This thesis provides a theoretical description of inelastic scanning tunneling spectroscopy(ISTS), using a newly developed first-principles approach, by combining time-dependentdensity functional theory and many-body perturbation theory. The Korringa-Kohn-Rostoker Green function method is utilized, since it affords a real-space description of nanostructures, well-suited to the ISTS context. The central quantity is the electron self-energy, containing the interactions between the tunneling electrons and the spin excitations of the nanostructure. This self-energy leads to a renormalized electronic structure in the vacuum region above the adsorbate, which can be directly compared with the experimental ISTS signal, in the spirit of the Tersoff-Hamann approximation. As a first application, the developed method is applied to individual 3$\textit{d}$ transition-metal adatoms (Cr, Mn, Fe, and Co) deposited on metallic surfaces (Cu(111) and Pt(111)). The obtained magnetic excitation spectra for the regarded structures show differences in the excitation lifetime and the $\textit{g}$ shift, which can be attributed to the electronic structure of both, the adsorbate and the substrate. The calculated theoretical inelastic spectra reveal different non-trivial shapes of the excitation signatures, that vary with distance to the adsorbate. Observed asymmetries in these spectra could explain asymmetries in experimental findings. Furthermore, some spectra show additional bound states (satellites) that are not predictable by use of a simple Heisenberg model. For Fe and Co adatoms on Pt(111) the impact of hydrogen contamination on the excitation spectrum is investigated. In agreement to experimental findings, the presence or absence of hydrogen has a significant impact on the shape of the excitation spectrum. In addition to the above analysis, we also consider clusters of two or more 3$\textit{d}$ transition-metal adatoms deposited on the Cu(111) surface, investigating the resulting magnetic excitation spectra. The magnetic moments are coupled by the exchange interaction which results in different excitation modes of acoustic and optical character. The obtained excitation spectra depend on the regarded adatom species, the interatomic distance, the alignment of the magnetic moments, the number of involved atoms, as well as the arrangement on the surface. A comparison of a ring and a chain structure reveals the impact of geometrical topology on magnetic excitations. The semiclassical Landau-Lifshitz-Gilbert model is used to provide an insightful interpretation of the first-principles spin-excitation modes. |
| Databáze: | OpenAIRE |
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