Browsing by Author "Peterseim, Tobias"

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    Organic conductors in equilibrium and nonequilibrium states : the interaction with electric and light pulses
    (2016) Peterseim, Tobias; Dressel, Martin (Prof. Dr.)
    In the framework of this thesis several organic conductors were extensively investigated by a variety of experimental and theoretical methods. Because of their rich phase diagrams, which can be controlled by varying temperature or hydrostatic pressure, they are an interesting playground to study different exotic ground states as well as electron-electron and electron-lattice interactions. Furthermore, theoretical models can be tested due to their low-dimensional character. Additionally, in the recent years the family of organic conductors has attracted more attention than nonlinear conductivity and photo-induced states have been discovered. Therefore, we have used steady state and time-resolved infrared spectroscopy and time-dependent conductivity measurements to examine the ground states as well as photo- and electronically induced states of the Fabre salts (TMTTF) 2X (X=PF6 , AsF6 , SbF6 , and ReO4), δ-(EDT-TTFCONMe2)2 AsF6 and Br, TTF-CA, and α-(BEDT-TTF)2I3. To support the experimental results, advanced DFT calculations were conducted to determine the band structure, the optical spectra and the molecular vibrations mode. By studying the infrared optical spectra of the Fabre salts, the charge disproportionation in the charge order phase has been determined very precisely following an almost linear behavior as a function of the transition temperature. With increasing transition temperature a crossover from a second order phase transition to a first order could be observed. Furthermore, we examined the ionic to neutral photo-induced phase transition in TTF-CA on the microsecond time range. The observed relaxation profile can be explained by a one-dimensional random-walk model of neutral-ionic domain walls. In α-(BEDT-TTF)2I3 the switching process from a low to a high conducting state has been systematically studied which is caused by the electronically excited high mobility charge carriers in the insulating phase. With this work, the ground states of the aforementioned organic conductors have been studied in detail and it was demonstrated that DFT calculations are an indispensable theoretical method to understand the experimental results. The time-resolved infrared spectroscopy has been introduced to the field of solid state physic by showing its capability on selected examples of electronically and photo-induced phase transitions which will pave the way for future studies.