| Infrared Spectroscopy is used to study a variety of unconventional electronic and magnetic materials. Through an analysis of the optical constants obtained from the experiment, the electronic structure, charge dynamics, and even magnetic properties of the materials may be uncovered. In this thesis two ferromagnetic systems, CrO2 and Ga1− xMnxAs, and three different superconductors, the heavy fermion CeCoIn5 and the copper oxide compounds HgBa 2CuO4 and Nd1.85Ce0.15CuO4−δ are studied. In ferromagnetic CrO2 a half metallic band structure is found from an analysis of the charge carrier scattering rate. In the ferromagnetic semiconductor, Ga1−xMn xAs, a sum rule analysis allows us to determine that the itinerant charge carriers are heavy, and therefore lie within an impurity band. We also observe a lightening of the mass below TC, indicating that the ferromagnetism is driven by these heavy carriers. By studying the normal state spectrum of σ1(ω) in the heavy fermion superconductor CeCoIn5 we find signs of charge carriers coupling to a collective mode. Investigation of the interplane response of both quasi two dimensional copper oxide superconductors reveals a large energy scale for the redistribution of spectral weight at T < TC. Additionally, in our study of the electron doped high temperature superconductor, Nd1.85Ce0.15CuO4−δ, we have made the first observation of the pseudogap state in this system, and find that the pseudogap energy scale is much larger than the superconducting gap. |
