We examine the spin angular momentum (SAM) density associated with the recently introduced [Phys. Rev. A 100, 053833 (2019)], partially coherent surface-plasmon-polariton (SPP) vortex fields at a metal-air interface. We show that the vortices appearing in such structured SPP fields induce a SAM density both in the interface plane and in the direction normal to the interface. We find that the radial and azimuthal SAM densities are caused solely by the SPP electric-field correlations. However, besides the intrinsic spin component induced by the complex SPP wave vector, the azimuthal SAM density remarkably carries also a spin component created by the elementary SPPs comprising the partially coherent vortex field. The normal SAM density, on the other hand, arises mainly due to the SPP magnetic-field correlations. Our analysis specifically demonstrates that the state of coherence of the partially coherent SPP vortex field plays an essential role in shaping the SAM density distributions. Our findings can find applications to near-field particle manipulation and in spin-based integrated photonic circuit design.

中文翻译：

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部分相干表面等离子体极化子涡旋场中的自旋密度

我们检查了与最近引入的 [ Phys. 修订版 A 100, 053833 (2019)]，金属-空气界面处的部分相干表面等离子体极化子 (SPP) 涡旋场。我们表明，出现在这种结构化 SPP 场中的涡流在界面平面和界面的法线方向上都会产生 SAM 密度。我们发现径向和方位角 SAM 密度仅由 SPP 电场相关性引起。然而，除了由复 SPP 波矢量引起的固有自旋分量之外，方位角 SAM 密度还显着地携带由构成部分相干涡旋场的基本 SPP 产生的自旋分量。另一方面，正常的 SAM 密度主要是由于 SPP 磁场相关性而产生的。我们的分析特别表明，部分相干 SPP 涡旋场的相干状态在塑造 SAM 密度分布方面起着至关重要的作用。我们的发现可以应用于近场粒子操纵和基于自旋的集成光子电路设计。