SURFACE FERMI CONTOURS AND PHONON ANOMALIES ON PT(111)

The surface Fermi contours of Pt(111) have been determined with use of high-resolution angle-resolved photoemission. There exist two surface resonances which produce distinct Fermi contours. The first contour is an approximately hexagonal electron pocket centered in the surface Brillouin zone and is very nearly degenerate with the edge of the projection of the sixth bulk band. The other contour is a more diffuse triangular electron pocket centered at KBAR, and is loosely associated with a projected gap in the fifth bulk band. These results do not support the suggestion that anomalies observed in measurements of the Pt(111) surface-phonon dispersion relations might be caused by screening singularities associated with surface-localized states. Our contours provide a guide for future phonon measurements searching for such anomalies.