Electronic structure of dense Pb overlayers on Si(111) investigated using angle-resolved photoemission

Dense Pb overlayers on Si(111) are important as the wetting layer for anomalous Pb island growth as well as for their own complex "devil's-staircase" phases. The electronic structures of dense Pb overlayers on Si(111) were investigated in detail by angle-resolved photoemission. Among the series of ordered phases found recently above one monolayer, the low-coverage root 7x root 3 and the high-coverage 14x root 3 phases are studied; they are well ordered and form reproducibly in large areas. The band dispersions and Fermi surfaces of the two-dimensional (2D) electronic states of these overlayers are mapped out. A number of metallic surface-state bands are identified for both phases with complex Fermi contours. The basic features of the observed Fermi contours can be explained by overlapping 2D free-electron-like Fermi circles. This analysis reveals that the 2D electrons near the Fermi level of the root 7x root 3 and 14x root 3 phases are mainly governed by strong 1x1 and root 3x root 3 potentials, respectively. The origins of the 2D electronic states and their apparent Fermi surface shapes are discussed based on recent structure models.