Correlated surface bands of the prototypical interface Sn/Si-alphaR3

International audience; Using angle-resolved inverse photoemission spectroscopy (KRIPES), we have investigated the unoccupied electronic structure of the model interface Sn/Si(1 1 1)-a-  3 p at room temperature. In addition to a ``metallic'' surface state crossing the Fermi level (E F) near the K H point, we unambiguously assign a second feature of our KRIPES spectra, located around 1.5 eV above E F , to a second surface state U H 2. We will experimentally show that U H 2 is an intrinsic feature of the a-  3 p reconstruction which cannot be associated with defects. The existence of these two surface states is not compatible with the ideal T 4 model which would show either a single, half-occupied metallic band crossing E F , or an insulating phase if strong correlation effects, important for these narrow surface bands, are considered. Rather, both U H 1 and U H 2 receive a natural explanation, once many-body effects are introduced, in the framework of a dynamical ¯uctuations 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. #