Superconductivity of small metallic particles. I

The ground state energy and orbital magnetic susceptibility of a small-particle superconductor are calculated with the use of perturbation theory, which is expected to give correct results in the limit of small particle size, i.e., when the average one-electron energy level spacing is much larger than the energy gap of the bulk metal. The method is applicable up to particles of intermediate size for which / = 1/4–1/2 (e.g., aluminum particles of radius 25–30 Å). The magnetic susceptibility does not undergo any drastic change in the region ~ when the particle size is varied, and quantum size effects do not show up in the susceptibility.Supported by a Grant-in-aid from the Japanese Ministry of Education.