Ultrahigh-resolution photoemission study of strongly correlated electron systems

Recent remarkable progress in the energy and momentum resolutions in photoemission spectroscopy has revealed the detailed electronic structure near the Fermi level (EF) of strongly correlated electron systems. The energy resolution has approached the characteristic energy scale which governs the anomalous physical properties of materials. We report here the recent development of high-resolution photoemission (HR- PES) study of strongly correlated f-electron materials based with Ce and U. Using HR-PES, we have found (1) Kondo resonance peak located just at EF in various metallic Ce compounds and its systematic evolution as a function of Kondo temperature, (2) Kondo-insulator (pseudo) gap in Ce compounds and its temperature dependence which characterizes the anomalous metal-insulator transition, and (3) Fermi surface of Ce and U compounds and its topological change accompanied with the magnetic phase transition as a function of temperature. We discuss the nature of 4f and 5f electrons in these compounds and possible models describing the anomalous physical properties based on the character of f electrons. (author)