Electronic structure of EuN: Growth, spectroscopy, and theory

and x-ray emission spectroscopies (XAS and XES) at the nitrogen K edge are compared to several different theoretical models, namely, local spin density functional theory with Hubbard U corrections (LSDA + U), dynamic mean field theory (DMFT) in the Hubbard-I approximation, and quasiparticle self-consistent GW (QSGW) calculations. The DMFT and QSGW models capture the density of conduction band states better than does LSDA + U. Only the Hubbard-I model contains a correct description of the Eu 4f atomic multiplets and locates their energies relative to the band states, and we see some evidence in XAS for hybridization between the conduction band and the lowest-lying 8 S multiplet. The Hubbard-I model is also in good agreement with purely atomic multiplet calculations for the Eu M-edge XAS. LSDA + U and DMFT calculations find a metallic ground state, while QSGW results predict a direct band gap at X for EuN of about 0.9 eV that matches closely an absorption edge seen in optical transmittance at 0.9 eV, and a smaller indirect gap. Overall, the combination of theoretical methods and spectroscopies provides insights into the complex nature of the electronic structure of thismaterial.TheresultsimplythatEuNisanarrow-band-gapsemiconductorthatliesclosetothemetal-insulator boundary, where the close proximity to the Fermi level of an empty Eu 4f multiplet raises the possibility of tuning both the magnetic and electronic states in this system.