Large Spin-to-Charge Conversion in Ultrathin Gold-Silicon Multilayers

TL;DR

This study demonstrates that ultrathin gold-silicon multilayers exhibit a significantly enhanced spin-charge conversion efficiency, primarily due to interfacial effects and the Rashba-Edelstein mechanism, with potential implications for spintronic devices.

Contribution

It provides the first detailed thickness-dependent analysis of spin-charge conversion in ultrathin Au/Si multilayers, highlighting the dominance of interfacial effects at nanometer scales.

Findings

Spin-charge conversion efficiency reaches 0.99 in 2 nm Au layers.

Interfacial spin-orbit coupling dominates in ultrathin Au.

Bulk spin Hall angle of gold is approximately 0.012.

Abstract

Investigation of the spin Hall effect in gold has triggered increasing interest over the past decade, since gold combines the properties of a large bulk spin diffusion length and strong interfacial spin-orbit coupling. However, discrepancies between the values of the spin Hall angle of gold reported in the literature have brought into question the microscopic origin of the spin Hall effect in Au. Here, we investigate the thickness dependence of the spin-charge conversion efficiency in single Au films and ultrathin Au/Si multilayers by non-local transport and spin-torque ferromagnetic resonance measurements. We show that the spin-charge conversion efficiency is strongly enhanced in ultrathin Au/Si multilayers, reaching exceedingly large values of 0.99 +/- 0.34 when the thickness of the individual Au layers is scaled down to 2 nm. These findings reveal the coexistence of a strong interfacial spin-orbit coupling effect which becomes dominant in ultrathin Au, and bulk spin Hall effect with a relatively low bulk spin Hall angle of 0.012 +/- 0.005. Our experimental results suggest the key role of the Rashba-Edelstein effect in the spin-to-charge conversion in ultrathin Au.