Many-body effects in the electronic structure of Sn/Si(111)-alpha-root 3

The unoccupied electronic structure of the model interface Sn/Si(1 1 1)-alp ha-root3 has been measured at room temperature (RT) using angle-resolved in verse photoemission spectroscopy (KRIPES). In addition to a partly occupied surface band crossing the Fermi level, there is a second unoccupied surfac e state located 1.5 eV above E-F; the existence of these two surface states is not compatible with the single adatom site used to describe the alpha-r oot3 reconstruction. These surface states receive a natural explanation, on ce many-body effects are introduced, in the framework of a dynamical fluctu ations model, where two types of adatom site, reminiscent of a possible low -temperature (3 x 3) phase, coexist at RT.