Correlated surface bands of the prototypical interface Sn/Si(1 1 1)-α-3

Using angle-resolved inverse photoemission spectroscopy (KRIPES), we have investigated the unoccupied electronic structure of the model interface Sn/Si(1 1 1)-α-3 at room temperature. In addition to a “metallic” surface state crossing the Fermi level (EF) near the K′ point, we unambiguously assign a second feature of our KRIPES spectra, located around 1.5 eV above EF, to a second surface state U2′. We will experimentally show that U2′ is an intrinsic feature of the α-3 reconstruction which cannot be associated with defects. The existence of these two surface states is not compatible with the ideal T4 model which would show either a single, half-occupied metallic band crossing EF, or an insulating phase if strong correlation effects, important for these narrow surface bands, are considered. Rather, both U1′ and U2′ receive a natural explanation, once many-body effects are introduced, in the framework of a dynamical fluctuations model, where two kinds of Sn adatoms sites reminiscent of a low-temperature 3×3 phase do persist at room temperature. Correlated surface bands incorporating many-body effects in a non restricted way provide a complete description of the experimental surface bands and their dispersions.