Browsing by Author "Pröpper, Daniel Christopher"

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    Spectroscopic ellipsometry of iridium oxides and iron pnictides
    (2014) Pröpper, Daniel Christopher; Keimer, Bernhard (Prof. Dr.)
    In physics many body effects are among to the most fascinating phenomena. Rather than the huge particle number accounting for the relevant interactions and correlations is most crucial to an adequate description. Strongly correlated electron systems offer the opportunity to study many body effects with a variety of interactions with variable strength - in particular competition of the latter in driving the system might lead to unforeseen properties. In this context the presented work focuses on two material classes, which have attracted much attention recently: compounds from the iridium oxide and iron pnictide families. Since electronic correlations directly affect the charge carrier dynamics in a specific material, which is characterized by its complex dielectric function, optical spectroscopy and in particular broadband spectroscopic ellipsometry is a suitable tool to address these questions from an experimental point of view. The thesis is organized in three parts. After laying out the essential theoretical and experimental principles, we discuss the results on the iridium oxides and iron pnictides. In Sr2IrO4, considered as the prototypical member of this iridium oxide family, we detect a strong optical out-of-plane anisotropy in good agreement with calculations within density-functional theory, which including the essential spin-orbit coupling. The related compound Na3Ir3O8 shows extraordinarily strong Fano resonances in the phonon spectra, which we assign to a lack of inversion symmetry and the strong spin-orbit coupling. This points to a non-negligible electron-phonon coupling in the iridium oxides. In the case of the iron pnictides we focus on the influence of structural changes on the electronic correlations. Here, isovalent substitution of Fe(3d) by Ru(4d) reveals a systematic reduction in the correlations in accordance with the doping phase diagram. A second approach is the detailed study of the temperature and broad range (FIR to UV) spectral dependence of the dielectric response of the representative parent compounds AFe2As2 (with A = Ca, Sr, Ba) in which we detect consistently two coupled subsystems of the spin-density-wave. While the coupling strength of the respective subsystems themselves decreases with increasing atomic number, the coupling between them gets stronger. Since the three investigated materials are driven superconducting upon doping, our results may provide insights into the physics of the related superconductors.