Fermi surface of a triangular lattice overlayer: Pb/Ge(111) alpha-phase

The alpha-(root 3 x root 3)R30 degrees phase of the Pb/Ge(111) interface ha s been extensively studied using angle-resolved photoemission (ARUPS). The contours of the Fermi surface have been measured by two-dimensional ARUPS m apping. The topology of the Fermi surface is characterized by an undulated shape, which resembles the results of theoretical calculations. The experim ental Fermi momentum along the TK and TM direction is 0.30+/-0.03 and 0.40/-0.03 Angstrom(-1), respectively. These values agree with the wave vector needed for a perfect 3 x 3 nesting. However, the Fermi surface topology exh ibits no large Bat areas suitable for electronic nesting, as required by a charge density wave stabilisation. (C) 1999 Elsevier Science B.V. All right s reserved.