Superconductor-insulator transition in ultrathin Pb films: Localization and superconducting coherence

We have measured temperature-dependent resistivities of a set of Pb ultrathin films by repeating in situ deposition at liquid-He temperature. Observed conductance in the fermion region can be described by a single-parameter scaling function (beta function) with a self-consistent theory for localization in two dimensions. Based on estimated values of electrical localization length (xi(loc)) and superconducting coherence length (xi(super)), the superconductor-insulator transition is confirmed to occur at the point where xi(loc)similar to 2 xi(super). Moreover, only samples exhibiting lnT dependence in the fermion region become global coherent superconductors at low temperature.