Plasmon-Driven Giant Amplification of Ultrashort Spin Current

TL;DR

This paper demonstrates that plasmon excitation in gold nanoparticles can significantly amplify ultrashort spin currents in a hybrid structure, advancing the development of efficient spintronic terahertz devices.

Contribution

It introduces a novel mechanism where plasmon excitation enhances spin current generation via electron-magnon scattering, especially in nanoparticle-based nanocavities.

Findings

Spin current amplification by two orders of magnitude due to plasmon excitation.

Enhanced THz emission linked to plasmon-induced heating effects.

Nanocavity design with insulator ferromagnet maximizes spin current enhancement.

Abstract

A key challenge in spintronics is to efficiently generate and manipulate spin current for information processing. Here we study ultrashort spin transport and associated terahertz (THz) emission in a hybrid structure comprising gold nanoparticles, a ferromagnet (FM) and a normal metal (NM) and show that plasmon excitation in the nanoparticles strongly enhances the electron-magnon scattering rate through heating effects, thereby amplifying the spin current generation at the FM$|$NM interface. This effect is even more pronounced when the FM is an insulator with a thickness much smaller than the nanoparticle size. In this case, the gold nanoparticle and NM substrate form a nanocavity with the FM as a dielectric layer, trapping plasmons inside the gap. The resulting spin current can be amplified by two orders of magnitude as compared to the case without plasmon excitations. Our findings provide a novel route to design efficient spintronic THz devices and further open the door to the interdisciplinary field of spintronics and nanophotonics.