Photoelectron spectroscopy on strongly correlated systems

Abstract: This work presents photoelectron spectroscopy data on somestrongly correlated systems. The electronic structure of the3dtransition metal oxides NiO and CoO have been studiedwith angle resolved and resonant photoemission. In the lattercase, both NiO and CoO show strong resonance effects at themetal absorption edges. Even though an atomic or cluster likepicture can account for a large part of resonant photoemissionresults, it seems that a model which includes translationalsymmetry will be needed to give an over all satisfactorydescription. There still exists some uncertainty, but it seemsthat the magnetic ordering in these compounds do not have acrucial impact on the electronic structure.Core level photoemission results on Bi2Sr2Ca1-xYxCu2O8+?is also included. Data collected onunderdoped samples as a function of doping are compared totemperature dependent data. The result indicates that thepseudo-gap observed in underdoped cuprate superconductors issimilar in nature to the superconducting gap observed inoptimum doped samples.Measurements on Ce compounds have been done and the resultscompared to the predictions of the Anderson impurity model.Results on CeB6and CeCu6are consistent with the model and indicate aweaker hybridization in CeCu6as compared to CeB6. In a comparative study of CeIn3single and poly-crystals, it is shown thatphotoemission give more bulk signal for the single-crystal thanthe poly-crystal. The resonance data on CeIn3contain more features than what is expected fromonly f electron emission. The extra feature is proposed tooriginate from the f weight of an In 5sp band hybridizing withthe Ce 4f level.