Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Co(0001) trilayers

TL;DR

This study investigates how superconductivity in epitaxial Nb/Au/Co trilayers is affected by ferromagnetic exchange and layer thickness, revealing long- and short-period oscillations in transition temperature linked to quantum interference effects.

Contribution

It provides detailed experimental evidence of oscillatory behavior in Tc related to Au layer thickness and compares effects between Co and Fe ferromagnets in epitaxial trilayers.

Findings

Long-period (2.1 nm) oscillation in Tc as a function of Au thickness.

Short-period (0.76 nm) oscillation observed for thin Au layers.

Oscillations attributed to RKKY-like spin polarization in Au.

Abstract

Epitaxially grown multilayer systems offer the possibility to study the influence of ferromagnetism on superconductivity in a new and controlled way. In this paper, we explore how the superconducting properties of high quality, epitaxially-grown superconductor/normal-metal/ferromagnet trilayers evolve as a function of the exchange splitting in the ferromagnet, and the thickness of the normal metal layer. We report results for Nb(110)/Au(111)/Co(0001), and make a detailed comparison with earlier results for Nb(110)/Au(111)/Fe(110). We use quantitative FFT analysis to confirm the existence of a long-period (2.1 nm) oscillation in the superconducting transition temperature Tc as a function of the Au-layer thickness tAu, for tAu>2 nm, and highlight an additional short-period (0.76 nm) oscillation for tAu<3 nm in Nb/Au/Co. This short-period oscillation can be explained in terms of a damped RKKY-like oscillation of the spin-polarization in Au. The robustness of the long-period oscillation against the substitution of Co for Fe suggests that it is intrinsic to the Au(111) layer on Nb, and may represent a new form of quantum interference in very clean trilayer systems.