Fermi surface and electronic structure of Pb/Ge(111)

The electronic structure of Pb/Ge(111) has been probed along the temperature-induced phase transition α-√3×√3R30^∘⇒3×3 using angle-resolved photoemission. The α-√3×√3R30^∘ phase is metallic due to the existence of a half-filled, dispersing surface band. The 3×3 phase is characterized by the appearance of an additional surface band with 3×3 periodicity, whose role in the phase transition is discussed. The Fermi-surface topology of the α-√3×√3R30^∘ phase has been probed using angle-resolved photoemission. Its shape is undulated, and it resembles strongly the theoretical prediction, with a Fermi momentum of 0.31 ^-1 along ΓK directions and 0.40 ^-1 along ΓM directions. These values were determined from different experimental methods, and agree with the values needed for a perfect 3×3 nesting. However, the Fermi surface exhibits no large flat areas suitable for electronic nesting.