Diamagnetic response of cylindrical normal-metal-superconductor proximity structures with low concentration of scattering centers

We have investigated the diamagnetic response of composite NS proximity wir es, consisting of a clean silver or copper coating, in good electrical cont act to a superconducting niobium or tantalum core. The samples show strong induced diamagnetism in the normal layer, resulting in a nearly complete Me issner screening at low temperatures. The temperature dependence of the lin ear diamagnetic susceptibility data is successfully described by the quasic lassical Eilenberger theory including elastic scattering characterized by a mean-free path l. Using the mean-free path as the only fit parameter we fo und values of I in the: range 0.1-1 of the normal metal-layer thickness d(N ), which are in rough agreement with the ones obtained from residual resist ivity measurements. The fits are satisfactory over the whole temperature ra nge between 5 mK and 7 K for values of d(N) varying between 1.6 and 30 mu m . Although a finite mean-free path is necessary to correctly describe the t emperature dependence of the linear-response diamagnetic susceptibility, th e measured breakdown fields in the nonlinear regime follow the temperature and thickness dependence given by the clean limit theory. However, there is a discrepancy in the absolute values. We argue that in order to reach quan titative agreement one needs to take into account the mean-free path from t he fits of the linear response. [S0163-1829(99)08809-8].