Josephson properties of Nb/Cu multilayers

The self-consistent equations, which have been derived recently as a microscopic model for the crossover between BCS superconductivity and Bose-Einstein condensation in a three-dimensional interacting Fermi system [R. Hausmann, Z Phys B 91, 291, (1993)[, are solved numerically by repeated Fourier transformation. We find a superfluid transition temperature T(c) which increases monotonically with increasing attractive coupling strength. Furthermore, we determine the chemical potential Μ, the fermion distribution function n(k), and the complex effective mass 2m(*) of the fermion pairs T=T(c). The bound fermion pairs cause a power-law tail ∼k(-4) in n(k) for large k and behave as short-living quasi-particles in the crossover region, which is indicated by a large imaginary part of 2m(*).