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K. Astleithner:
"Optical conductivity in the Falicov-Kimball model: a dual fermion perspective";
Betreuer/in(nen): K. Held, T. Ribic, A. Kauch; E138, 2019; Abschlussprüfung: 2019.

The Falicov-Kimball model (FKM) is one of the simplest models to describe correlation effects in solid systems. It can be solved semi-analytically in dynamical mean field theory (DMFT), where all purely local correlations between electrons are taken into account and therefore within DMFT a good description of phenomena such as the metal-to-insulator transition is obtained. However, the charge density wave fluctuations that dominate the physics of the FKM and lead to a phase transition into an ordered state emerge from nonlocal correlations. To include such nonlocal correlations, diagrammatic extensions of DMFT have been developed recently. One of these methods, the dual fermion (DF) approach, is employed in this thesis to analyze the effect of nonlocal correlations. Especially, the effect of such nonlocal vertex corrections onto the optical conductivity describing the interaction of light with the system is investigated. It is shown that besides well-known phenomena, such as weak localization, a new form of bosonic optical excitations, coined -tons, is prevalent in the FKM.

http://repositum.tuwien.ac.at/obvutwhs/content/titleinfo/3601320