Resistivities and mean free paths in individual layers of a metallic multilayered structure

Abstract

There exists in the literature a number of transport measurements performed on metallic superlattices. In this paper a method is proposed which, given such measurements performed at two different temperatures, allows determination of resistivities and mean free paths (MFP’s) of carriers in individual layers comprising a superlattice. The method is illustrated for Nb/Al (author’s data) and Nb/Cu (data of Werner, Banerjee, Yang, Falco, and Schuller). The behavior of the MFP in individual layers as a function of layer thickness turns out to be both unexpected and instructive. In particular, we find that in all cases except for Cu in Nb/Cu, the MFP is significantly (factor of 2–3) smaller than the layer thickness. Previously, for the lack of such information, it was uniformly assumed that the MFP is limited by the layer thickness, L∼d. Knowledge of the MFP is important for interpretation of various experiments on metallic superlattices, in particular for better understanding of superconducting proximity systems and tunneling measurements.