Superconductivity in ultrasmall metallic particles

Recent single electron transport experiments in nanometer size samples renewed the question about the lower limits of the size of superconductors, and the crossover from superconducting to normal state. In order to give answers to these questions, a pairing Hamiltonian for fixed number of particles is studied including the degeneracy of levels around the Fermi energy. For d-fold degenerate states we find that the ratio of two successive parity parameters Δ p is nearly 1 + l/d.