Mesoscopic superconductors as 'artificial atoms' made from Cooper pairs

The superconducting coherence length ξ = ℏvF/Δ characterizes the spatial extent of Cooper pairs and, in practice, can be as large as several microns. If such quasi-particles are squeezed in a small volume, their wavefunctions become strongly modified and, therefore, mesoscopic superconductors can be expected to exhibit properties radically different from a bulk material. We have studied the influence of quantum confinement on the superconductivity of individual grains with size down to 100 nm and observed plenty of exotic features in their behavior that changes very rapidly upon changing their size. In this paper, we focus on those features which relate to the presence of discrete quantum states of the Bose condensate and emphasize extended similarities between the physics of mesoscopic superconductors and 'artificial atoms'. © 1998 Elsevier Science B.V. All rights reserved.