Itinerant Nature of U 5f States in Uranium Mononitride UN Revealed by Angle Resolved Photoelectron Spectroscopy

The electronic structure of the antiferromagnet uranium nitride (UN) has been studied by angle-resolved photoelectron spectroscopy (ARPES) using soft x-rays ($h\ensuremath{\nu}=420$\char21{}520 eV). Strongly dispersive bands with large contributions from the U $5f$ states were observed in ARPES spectra and form Fermi surfaces. The band structure as well as the Fermi surfaces in the paramagnetic phase are well explained by the band-structure calculation treating all the U $5f$ electrons as being itinerant, suggesting that an itinerant description of the U $5f$ states is appropriate for this compound. On the other hand, changes in the spectral function due to the antiferromagnetic transition were very small. The shapes of the Fermi surfaces in a paramagnetic phase are highly three-dimensional, and the nesting of Fermi surfaces is unlikely as the origin of the magnetic ordering.