Electronic structure and Fermi surface of two-dimensional rare-earth silicides epitaxially grown on Si(111)

The electronic structure and the Fermi surface of two-dimensional rare-earth silicides epitaxially grown on Si(111), YSi₂ and GdSi₂, have been studied by a combination of angle-resolved ultraviolet photoemission spectroscopy and density functional theory calculations. Both silicides present a very similar electronic structure, with two characteristic electronic bands below the Fermi energy. One crosses the Fermi energy near the Γ point of the surface Brillouin zone (hole pocket) and the other one close to the M̄ point (electron pocket). These two bands arise from surface (localized) states and are responsible for all the Fermi surface features. The theoretical calculations are in good qualitative agreement with the experimental results, and also allow to examine the nature of the bonding between the rare earth and the neighboring silicon atoms. We have found a combination of sp metallic type bond together with covalent bonds involving the rare-earth d states and Si $3p$ states.