Surface electronic structure of Tm(0001) and Yb(111)

Occupied d-like surface states were observed for the close-packed surfaces of Tm(0001) and Yb(111) metal films grown epitaxially on W(110) and Mo(110) substrates, respectively. In the case of Tm metal, the surface state exhibits almost no dispersion and is extended over the whole surface Brillouin zone, while in the case of Yb metal, it is restricted to a narrow region around the {Γ}{} point. The surface shifts of the 4f binding energies on these close-packed surfaces were determined to be 0.47±{}0.05 eV for Tm(0001) and 0.45±{}0.03 eV for Yb(111). Both values are substantially smaller than reported previously for polycrystalline surfaces of the two metals. State-of-the-art band-structure calculations, based on density-functional theory, predict a flat surface state slightly above the Fermi energy. There is no obvious explanation for this inconsistency at the present time.