Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 25: Phase Transitions
O 25.4: Vortrag
Dienstag, 27. März 2007, 12:00–12:15, H41
Structural implications of the 1d-2d-transition in Pb wires on Si(557) — •Marcin Czubanowski, Shima Akbari, Christoph Tegenkamp, and Herbert Pfnür — Instittut für Festkörperphisik Leibniz Universität Hannover
The adsorption of Pb on Si(557) substrates leads to the formation of anisotropic metallic structures as revealed by conductivity measurements, STM and ARPES. The annealing of at least 1ML Pb to 640K forms atomic chain structures, which show below Tc=78K a metallic conductance along the wires (110), whereas in the (1 12) direction an insulating behavior is found. This quasi one-dimensional conductance below Tc is originated by complete Fermi nesting in the direction normal to the structure and split-off valence bands with mesoscopic Fermi-wavelengths along the Pb-chains. These observations are coupled with structural changes that were investigated systematically close to Tc by SPA-LEED experiments described here. The Pb-chains reorganize the structure of Si(557) substrate into [223] facets with 42/3 Si unit cells in the [112] direction, as seen by a spot-splitting of 21,3%. This terrace structure undergoes a reversible incommensurate-incommensurate phase transition at Tc, which increases the average interchain distance d and destroys the perfect nesting condition. Simultaneously, the Pb-induced regularly spaced domain wall network, as evident from a 10-fold splitting of the √3 structure, disappears. These findings explain qualitatively the observed transport properties, as will be shown.