Abstract
We propose and analyze surface-plasmon-driven electron spin currents in a thin metallic film. The electron gas in the metal follows the transversely rotating electric fields of the surface plasmons (SPs), which leads to a static magnetization gradient. We consider herein SPs in a thin-film insulator–metal–insulator structure and solve the spin diffusion equation in the presence of a magnetization gradient. The results reveal that the SPs at the metal interfaces generate spin currents in the metallic film. For thinner film, the SPs become strongly hybridized, which increases the magnetization gradient and enhances the spin current. We also discuss how the spin current depends on SP wavelength and the spin-diffusion length of the metal. The polarization of the spin current can be controlled by tuning the wavelength of the SPs and/or the spin diffusion length.
Highlights
Surface plasmons (SPs) are excitations localized at a metal-dielectric interface and are composed of electromagnetic waves coupled with plasma oscillations of the electron gas in the metal
We study whether spin accumulation δμ, which drives spin currents, is generated by the source term that stems from the surface plasmons (SPs)-induced magnetization gradient: jssou = − mσ0 ∇My. (21) Here we focus on the stationary state of the system
We derived the eigenmodes of surface plasmons (SPs) in a thin-film system and calculated their spin angular momentum
Summary
Surface plasmons (SPs) are excitations localized at a metal-dielectric interface and are composed of electromagnetic waves coupled with plasma oscillations of the electron gas in the metal. The spin direction is uniquely determined by the propagation direction and the decay direction [2] This is the so-called spin momentum locking effect of evanescent waves, and is observed in many systems, such as in total internal reflection configuration, in optical fibres, and lossy interfaces [3–6]. There is a mechanism where plasmonmagnon interaction produces spin currents at metal-magnetic material interfaces [18,19] Compared to these previous studies, the significant point in our study is that the transverse spin of the SPs in the thin film together with the spin-momentum locking can be an alternative way to generate pure spin currents from light without any magnetic field or magnetic substances.
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