It was shown that a fluctuating incommensurate domain wall structure, such as that hypothesized for clean Ge(111) above 540K, plus an observed weakly-metallic behavior, could be mutually related. The wall structure implied a liquid of defects, adatom trimers at the intersection of 3 concurrent topological walls, that carried fractional charge; with one half extra electron each. These electrons were de-localized among the defects, thus giving rise to a narrow-band 2-dimensional metal whose Fermi-level density of states grew with the density of walls and therefore with temperature. This model agreed closely with new photo-emission measurements which had been carried out on Ge(111) across the 540K transition, and beyond.

Fractional Surface Doping by Topological Neutral Wall Intersections on Ge(111). G.Ballabio, A.Goldoni, S.Modesti, E.Tosatti: Physical Review Letters, 2001, 87[18], 186802 (4pp)