Atomic-size metallic conductors.

Abstract

A number of newly developed experimental techniques and theoretical insights have made it possible to investigate the electronic transport properties of conductors at the atomic scale. Although the field is still rapidly evolving, a number of new discoveries, concepts and insights have been clearly established. The central theme of this brief review will be the electronic conductance of a single atom. This conductance can be described in terms of a number of quantum modes, where the number of these modes is determined by the valence orbitals of the metal atom. I first present some elements of the theoretical basis for these concepts, and discuss the various experimental tools that have been used to verify it. Electronic conductance at the atomic scale cannot be separated from the problem of the energetics and dynamics of atomic-scale configurations. Investigations in this area have produced a number of surprising discoveries, and of these I will discuss the spontaneous formation of a conducting chain of single gold atoms, and the enhanced stability of nanowires of alkali metals at 'magic' radii determined by shell structure of the conductance modes.