Interface Properties of Superconductor-Based Heterostructures from Critical Temperature Measurements

Abstract

We report the experimental method of the evaluation of the specific boundary resistance, R _B , of superconductor (S)/non-superconductor (NS) interfaces by measuring the superconducting critical temperature, T _c , as a function of the thickness of the superconducting layer, d _S , in S/NS hybrids and of the number of S/NS bilayers, N _bl, for a large number of N _bl in NS/[S/NS]$_{N_{\mathrm{bl}}}$ 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), Cu_0.38Ni_0.62, was chosen for NS. Analyzing the experimental results by solving exactly the Usadel equations, we were able to unambiguously determine the value of R _B 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/Cu_0.38Ni_0.62.