Groupe de Physique Statistique

The segregation of boron (B) atoms at the silicon (111) surface leads to a 3x3R30° surface reconstruction. The adsorption of potassium adatoms (K), electron donor, on preferential sites, leads to the formation of a dangling bond-type surface state in the semi-conducting gap. The amount of K controls the filling such as at a coverage of 1/3 of mono-layer, the surface band is half-filled. The surface-enhanced electronic correlations have been shown to induce a metal-insulator transition with the opening of a Mott gap on sp-type bands ten years ago [1]. Such a Mott transition has been recently reported in Sn/Ge(111) at low temperature and is known to exist in other semi-conducting surface presenting a triangular pattern [2]. The formation of a frustrated magnetic triangular network at surface has been proposed with a possible magnetic ordering at low temperature in a non-colinear Néel phase [3]. Experimental results are strongly needed to evidence the possibility to observe magnetism at low-T (may be superconductivity) since these semi-conducting surfaces are good candidates to form hole-doped frustrated magnets. We report here on Auger spectroscopy, LEED and STM results to characterize and control the K/Si(111)3x3R30°-B interface. Then, ARPES is used to probe the effect of strong correlations in the surface state properties. Here we report two dispersive features characterizing the surface band whose temperature dependence has been measured [4]. An attempt to analyze the photoemission spectral function A(k,) in term of electron-magnon and/or electron-phonon interaction is presented.[1] H.H. Weitering et al., Phys. Rev. Lett. 78, 1331(1997); [2] R. Cortes et al., Phys. Rev. Lett. 96 126103 (2006) and references therein; G. Santoro et al., Phys. Rev. B 59, 1891 (1999);[3] L.O. Manuel et al., Phys. Rev. B 69, 184407 (2004). [4] L. Cardenas et al., to be published (2007).