Electronic States of $UNi_2$ from Photoemission Spectroscopy

We measured the angle-resolved ultraviolet and X-ray photoemission spectra of $UNi_2$ single crystal. The valence band angle-resolved ultraviolet photoemission spectra were compared to the accessible band structure calculations. For $UNi_2$ the lowest binding energy strong emission at about -0.1 eV comes from U 5f states and overlaps with the Fermi edge. A small feature at -0.6 eV was ascribed also to U 5f electrons with more localised character. The higher-energy two-peak structure at about -1.2 eV and -2.1 eV comes from Ni 3d states. X-ray photoemission spectroscopy shows the standard two-line spin-orbit splitting of the Ni 2p states and of the U 4f states. Some hybridisation of the Ni 3d and U 5f state was observed in the spectra. The pronounced satellites to the Ni 2p and 3p states, associated with the on-site Coulomb repulsion and other electron correlation energies, were observed.