Paramagnetic reentrant effect in high purity mesoscopic AgNb proximity structures

We discuss the magnetic response of clean Ag coated Nb proximity cylinders in the temperature range 150 mu K < T < 9 K. In the mesoscopic temperature regime, the normal-metal-superconductor system shows the yet unexplained paramagnetic reentrant effect, discovered some years ago [P. Visani, A. C. Mota, and A. Pollini, Phys. Rev. Lett. 65, 1514(1990)], superimposing on full Meissner screening. The logarithmic slope of the reentrant paramagnetic susceptibility chi(para)(T) proportional to exp(-L/xi(N)) is limited by the condition xi(N) = n L, with xi(N) = hv(F)/2 pi k(B)T, the thermal coherence length and n = 1,2, 4. At the lowest temperatures, chi(para) compensates the diamagnetic susceptibility of the whole AgNb structure.