High-resolution photoemission study of UNi₂Al₃ and URu₂Si₂

High-resolution low-temperature photoemission spectroscopy was performed for UNi₂Al₃ and URu₂Si₂ to study the nature of 5f electrons in U-based heavy fermion materials. Photoemission spectra of both compounds have a sharp peak at EF and a large broad peak around 2 eV, while only UNi₂Al₃ exhibits an additional small broad feature at 0.6 eV. The two features in the vicinity of EF (the EF-peak and the small structure at 0.6 eV) were found to have a dominant U 5f character. Comparison with the band structure calculations and experimental results on UPd₂Al₃ suggests that the EF-peak is ascribed to itinerant U 5f electrons while the following broad feature at 0.6 eV represents localized f electrons.