Infrared magneto-optical studies of correlated electron systems: Faraday and Kerr measurements in gallium manganese arsenide, strontium ruthenium oxide and praesodymium cerium copper oxide
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This thesis presents experimental Faraday and polar Kerr effect studies in the mid and near infrared energy spectra of several materials with strong electronic correlations: ferromagnetic semiconductors Ga 1-x Mn x As, high temperature superconductors Pr 2-x Ce x CuO 4 and ferromagnetic metals SrRuO 3 . The thesis is centered on the study of the Ga 1-x Mn x As films and in particular on their band structure. Magneto-optical Faraday and polar Kerr effect experimental results are presented for a series of Ga 1-x Mn x As samples grown by two different techniques and having distinct ferromagnetic properties. Since these measurements directly probe the changes in the band structure brought by the presence of magnetization, they can distinguish between the paramagnetic and ferromagnetic signals. Strong features observed in the Kerr and Faraday angles, coming from the ferromagnetic component, are consistent with the valence band model calculations that determine the band structure in the k*p method. Band renormalization effects have to be considered in order to account for the position of these features. The origin of the metal to insulator transition is studied in samples intentionally doped with compensating ions (Te). We also present the results on a delta doped superlattice structure. In addition to ferromagnetic Ga 1-x Mn x As, our preliminary studies in high temperature superconductors and ruthenate perovskites shows promising results. We were able to show direct evidence of contributions from the antiferromagnetic phase in underdoped and optimal doped Pr 2-x Ce x CuO 4 . Furthermore, the rich and strong IR Faraday and Kerr response in SrRuO 3 will be critical in understanding its complex electronic structure.