The surface electronic structure of Br/Pt(1 1 0) phases

The surface electronic structure of c(2×2)-Br/Pt(1 1 0) and (3 × 1)-Br/Pt(1 1 0) is examined by angle-resolved UV photoemission. The (3 × 1) phase was previously shown to be associated with a charge density wave (CDW). In the present study we investigate, whether the CDW instability is caused by a saddle point mechanism or rather by Fermi surface nesting. Although we find saddle points in the (3 × 1) phase, it is not clear yet, whether they contribute significantly to the energetic stabilization of the CDW. So far, conventional Fermi surface nesting seems to be an equally likely explanation. Many-body effects are identified in the spectra.