Valence Band Photoemission Study of the Kondo Insulator CeNiSn

The electronic structure of the Kondo insulator CeNiSn has been investigated by using photoemission spectroscopy. A satellite feature is observed in the valence band spectrum about 6 eV below the Ni 3d main peak, indicating a strong Ni 3d Coulomb correlation in CeNiSn. The Ce 4f partial spectral weight exhibits three peak structures, including one due to the 4f¹ → 4f^0 transition, another near E_F, and the other which overlaps the Ni 3d main peak. We interpret the peak near E_F as reflecting mainly the Ce 4f/Sn 5p hybridization, whereas that around the Ni 3d main peak as reflecting both the Ce 4f/Ni 3d and Ce 5d/Ni 3d hybridization. Yield measurements across the 4d → 4f threshold indicate the Ce valence to be close to 3+. The prominent Fermi edge suggests a metallic ground state in CeNiSn.