COMPETITION BETWEEN SURFACE ROUGHENING AND RECONSTRUCTION IN (110) FACETS OF FCC CRYSTALS

Surface roughening induces a simultaneous deconstruction transition in missing-row-reconstructed (110) facets of fcc crystals. This transition can be described by the four-state chiral clock-step model. Numerical finite-size-scaling results indicate that at zero chirality this transition has the character of a superimposed Kosterlitz-Thouless-type roughening and an Ising-type deconstruction transition. A symmetry property of the model, called S-T invariance, and related to supersymmetry, elucidates this aspect. In the strong chirality limit a fermion analysis applies. The full phase diagram can be constructed by combining these numerical and analytical results. Pt(110) and Au(110) follow specific paths through it. The only path consistent with the current experimental evidence for Pt(110) is a roughening-induced simultaneous deconstruction transition, which has the character of an incommensurate melting transition with respect to the reconstruction degrees of freedom. This implies that the difference in energy between clockwise and anticlockwise steps is small in Pt(110).