Interplay of Charge Order and Superconductivity: Optical Properties of Quarter-Filled Two-Dimensional Organic Conductors and Superconductors

In this thesis the optical properties of quasi two-dimensional organic molecular crystals are investigated. Within this class of materials some systems are metallic, some are insulating due to charge-order, and others even become superconducting. The driving force behind the ground states is the di"erent degree of e"ective electronic correlations. Recent experimental and theoretical studies of strongly correlated materials suggest that "uctuations of the ordered state may mediate superconductivity. The intention of this work is to prove the presence of such charge "uctuations and reveal their relation to superconductivity. To do this, we investigated BEDT-TTF based organic conductors by optical spectroscopy covering a broad frequency (8-20000 cm-1 ) and temperature (1.8-300 K) range using FTIR- and THz-spectrometers. In addition, the transport properties are investigated by dc four-point contact measurements and microwave cavity perturbation technique.