High-resolution photoemission study of strongly correlated f electron systems

The importance and powerfulness of high-resolution photoemission spectroscopy in studying the strongly correlated f electron systems are demonstrated by presenting recent results on some Ce and U compounds. Using angle-resolved photoemission spectroscopy (ARPES), we observed a clear change in the Fermi-surface volume accompanied by the magnetic phase transition in CeSb, showing an important role of temperature-dependent p-f mixing in dominating the electronic and magnetic properties. It was also found by ARPES that USb, which is isostructural to CeSb but has 5f electrons instead of 4f electrons in the outermost shell, has a Fermi-surface topology totally different from that of CeSb, indicating the different nature between 4f and 5f electrons. The ARPES result has elucidated the dual (itinerant and localized) character of 5f electrons in USb. We found a temperature-dependent energy pseudogap at E_F in CeRhSb and CeRhAs at low temperature, which is ascribed to the 'Kondo-insulator gap' formed through the hybridization between f and conduction electrons.