Electronic structure of black SmS. II. Angle-resolved photoemission spectroscopy

We have studied the electronic band structure of semiconducting black SmS with high-resolution angle-resolved photoemission spectroscopy (ARPES). The valence band consists of two well-separated groups of bands: almost nondispersive bands near E_F and highly dispersive bands at higher binding energy. The former is ascribed to the Sm²⁺ (4f⁶→4f⁵) multiplet and the latter to mainly the S 3p states. We found a small but distinct energy dispersion in the Sm 4f-derived bands near E_F. This indicates a strong hybridization between the "localized" Sm 4f electrons and the "itinerant" conduction electrons, leading to the "delocalized" Sm 4f states in mixed-valent SmS. We have compared the present ARPES results with a recent periodic Anderson model calculation.