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Fermi surfaces and energy gaps in Sn/Ge(111)
Journal of Physics: Condensed Matter (2001)
  • T.C. Chiang, University of Illinois at Urbana-Champaign
  • M.Y. Chou, Georgia Institute of Technology
  • Tim Kidd, University of Northern Iowa
  • T. Miller, University of Illinois at Urbana-Champaign
One third of a monolayer of Sn adsorbed on Ge(111) undergoes a broad phase transition upon cooling from a (×)R30° normal phase at room temperature to a (3×3) phase at low temperatures. Since band-structure calculations for the ideal (×)R30° phase show no Fermi-surface nesting, the underlying mechanism for this transition has been a subject of much debate. Evidently, defects formed by Ge substitution for Sn in the adlayer, at a concentration of just a few percent, play a key role in this complex phase transition. Surface areas near these defects are pinned to form (3×3) patches above the transition temperature. Angle-resolved photoemission is employed to examine the temperature-dependent band structure, and the results show an extended gap forming in k-space as a result of band splitting at low temperatures. On account of the fact that the room temperature phase is actually a mixture of (×)R30° areas and defect-pinned (3×3) areas, the band structure for the pure (×)R30° phase is extracted by a difference-spectrum method. The results are in excellent agreement with band calculations. The mechanism for the (3×3) transition is discussed in terms of a response function and a tight-binding cluster calculation. A narrow bandwidth and a small group velocity near the Fermi surface render the system highly sensitive to surface perturbations, and formation of the (3×3) phase is shown to involve a Peierls-like lattice distortion mediated by defect doping. Included in the discussion, where appropriate, are dynamic effects and many-body effects that have been previously proposed as possible mechanisms for the phase transition.
Publication Date
December 7, 2001
Citation Information
T.C. Chiang, M.Y. Chou, Tim Kidd and T. Miller. "Fermi surfaces and energy gaps in Sn/Ge(111)" Journal of Physics: Condensed Matter Vol. 14 Iss. 1 (2001)
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