Valence instability of the samarium metal surface

Abstract

The stability of the surface of the samarium and thulium metals against a divalent state is investigated within the pair-bonding model. Thereby it is found that a divalent surface is favored in samarium and close to becoming stable in thulium. The position of the surface divalent samarium ${f}^{6}$ level relative to the Fermi energy is calculated and compared with experiments. Also the surface core-level shifts for the europium and ytterbium metals are considered. Finally some interesting possible physical consequences of the divalent samarium surface layer are pointed out.