Proximity Effect in Nb/Au/CoFe Trilayers

TL;DR

This study examines how the superconducting critical temperature in Nb/Au/CoFe trilayers varies with layer thicknesses, revealing behaviors consistent with proximity effect theory and identifying interface properties.

Contribution

It provides experimental data on Tc behavior in Nb/Au/CoFe trilayers and compares results with Usadel formalism, highlighting a small oscillation unexplained by current theory.

Findings

Tc increases rapidly at small Au thickness and then saturates.

Non-monotonic Tc variation with CoFe thickness shows a shallow dip.

Quantitative interface parameters for Nb/Au and Au/CoFe are obtained.

Abstract

We have investigated the superconducting critical temperatures of Nb/Au/CoFe trilayers as a function of Au and CoFe thicknesses. Without the CoFe layer the superconducting critical temperatures of Nb/Au bilayers as a function of Au thickness follow the well-known proximity effect between a superconductor and a normal metal. The superconducting critical temperatures of Nb/Au/CoFe trilayers as a function of Au thickness exhibit a rapid initial increase in the small Au thickness region and increase slowly to a limiting value above this region, accompanied by a small oscillation of Tc. On the other hand, the superconducting critical temperatures of Nb/Au/CoFe trilayers as a function of CoFe thickness show non-monotonic behavior with a shallow dip feature. We analyzed the Tc behavior in terms of Usadel formalism and found that most features are consistent with the theory, although the small oscillation of Tc as a function of the Au thickness cannot be accounted for. We have also found quantitative values for the two interfaces: Nb/Au and Au/CoFe.