Sn/Ge(111) Surface Charge-Density-Wave Phase Transition

Angle-resolved photoemission has been utilized to study the surface electronic structure of 1/3 monolayer of Sn of Ge(111) in both the room-temperature (√3 × √3)R30° phase and the low-temprature (3 × 3) charge-density-wave phase. The results reveal a gap opening around the (3 × 3) Brillouin zone boundary, suggesting a Peierls-like transition despite the well-documented lack of Fermi nesting. A highly sensitive electronic response to doping by intrinsic surface defects is the cause for the unusual behaior, and a detailed calculation illustrates the origin of the (3 × 3) symmetry