By Aliaksei Charnukha
This thesis combines hugely exact optical spectroscopy facts at the lately came upon iron-based high-temperature superconductors with an incisive theoretical research. 3 impressive effects are suggested: (1) The superconductivity-induced amendment of the far-infrared conductivity of an iron arsenide with minimum chemical disease is quantitatively defined by way of a strong-coupling thought for spin fluctuation mediated Cooper pairing. The formalism built during this thesis additionally describes earlier spectroscopic information on extra disordered compounds. (2) an analogous fabrics show a pointy superconductivity-induced anomaly for photon energies round 2.5 eV, orders of importance greater than the superconducting power hole. the writer offers a qualitative interpretation of this unheard of remark, that's in response to the multiband nature of the superconducting nation. (3) The thesis additionally develops a entire description of a superconducting, but optically obvious iron chalcogenide compound. the writer indicates that this hugely strange habit should be defined end result of the nanoscopic coexistence of insulating and superconducting levels, and he makes use of a mix of 2 complementary experimental tools - scanning near-field optical microscopy and low-energy muon spin rotation - to without delay photograph the part coexistence and quantitatively be certain the section composition. those info have very important implications for the translation of information from different experimental probes.