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We present data of a study of four-point conductance of adsorbed Pb films on Si(557) in the thickness range between 0.6 up to several monolayers (ML) at various annealing stages. These measurements are combined with tunneling microscopy (STM). Onset of conductance is found close to the percolation limit. Pb layers annealed to room temperature are characterized by activated contributions to conductance up to 3 ML, a purely metallic temperature dependence at thicker layers, and an anisotropy of at most a factor of 2. On the contrary, annealing to 640 K, leaving only the first monolayer on the Si(557) surface results in extremely high surface state conductance which is quasi one–dimensional below a critical temperature of Tc=78 K, associated with an order–disorder phase transition. Induced by a 10-fold superperiodicity along the Pb chains and their lateral ordering, the system switches from low to high conductance anisotropy, with a metal–insulator transition in the direction perpendicular to the chain structure, while in the direction along the chains conductance with a 1/T + const. temperature dependence was found.

The electronic properties of thin metallic films strongly depend on their structure. For the preparation of ultrathin films (0.8 to 12 ML) Pb was grown on a Si (111)-7×7 structure at temperatures below 25 K. Percolation as measured by DC conductance starts at 0.7 ML. Up to 4 ML the growing film is disordered. During continuation of the growth the film recrystallizes epitaxially and layer-by-layer growth connected with oscillations of conductivity and LEED intensities is observed even at 25 K. The defect structure as determined by SPA-LEED and the quantum size effect allow a quantitative description of the conductivity oscillations. The experiments show, that the electronic properties of ultrathin Pb films are clearly correlated with the structural properties of the film.

The velocities of acoustic modes have been measured on SrTiO3 by Brillouin and neutron scattering. Anomalies are detected at or below T q, the temperature that marks the onset of the quantum paraelectric regime. It is shown quantitatively that the square of the polarization plays an important role below T q. The dependence on the wavevector square which is found for some of the anomalies indicates the importance of coupling terms proportional to the gradient of the polarization.

We show in a combined study of four-point conductance measurement and tunneling microscopy that surface state conductance induced by one monolayer of Pb on Si(557) can be quasi one dimensional with conductivity values close to typical three-dimensional metals. At a critical temperature of Tc=78K, associated with an order-disorder phase transition and a tenfold superperiodicity along the Pb chains, the system switches from low to high conductance anisotropy, with a semiconductor-insulator transition in the direction perpendicular to the chain structure, while along the chains conductance with a (1/T+const) temperature dependence was found. © 2005 The American Physical Society.