Proximity effect and interface transparency in Nb/Cu multilayers

Abstract

The interface transparency T is quantitatively studied in Nb/Cu multilayers. The dependence of the critical temperature Tc on both the thickness of superconducting layers dS in Cu/Nb/Cu trilayers and on the number of Nb/Cu bilayers Nb in Cu/[Nb/Cu]Nb multilayers is considered. The experimental results are analyzed on the base of the exact solution of Usadel equations. We obtain that there is an infinite number of pairs of (T, N) (N being the normal metal coherence length) which describes the measured Tc(dS) dependence with the same accuracy. This degeneracy is removed if the experimental Tc(Nb) dependence is analyzed. This allows to unambiguously determine, without the need of an independent estimation of N, the value of T for our system. This general method turns out to be especially useful when dealing with superconducting/ normal metal hybrids for which microscopic parameters are not well determined.