Conductance and mechanical properties of atomic-scale metallic contacts

We present a simple model for the evolution of atomic-scale contacts together with exact free-electron calculations of the conductance during an elongation-contraction process. The critical pressure that the neck call sustain before yielding is constant. Shortly before the neck breaks, the pressure gradually increases up to a maximum for a single atom contact. In force microscopy experiments this maximum value depends on the cantilever constant. Conductance histograms show clear peaks at integer multiples of 2e(2)/h slightly shifted to lower values. The dependence of the conductance of ballistic wires on the work function of different metals is also analyzed. We show that quantum finite-size effects can be taken into account by a simple correction to the Sharvin formula. Different sources of errors in the determination of actual cross-sections in atomic-scale contacts from conductance measurements are discussed.