Interface Properties of Superconductor-Based Heterostructures from Critical Temperature Measurements

We report the experimental method of the evaluation of the specific boundary resistance, RB, of superconductor (S)/non-superconductor (NS) interfaces by measuring the superconducting critical temperature, Tc, as a function of the thickness of the superconducting layer, dS, in S/NS hybrids and of the number of S/NS bilayers, Nbl, for a large number of Nbl in NS/[S/NS]Nbl multilayers. Two types of systems have been studied. We choose Nb as the S material for both types and Cu for a normal metal (N) for the first one. In the second case, a weakly ferromagnetic alloy (F), Cu0.38Ni0.62, was chosen for NS. Analyzing the experimental results by solving exactly the Usadel equations, we were able to unambiguously determine the value of RB for both the S/N and S/F hybrids. The results show that Nb/Cu is characterized by a lower value of the interfacial specific resistance with respect to the case of Nb/Cu0.38Ni0.62.