The study of spin–orbit coupling (SOC) of light is crucial to explore the light–matter interactions in sub-wavelength structures. By designing a plasmonic lattice with chiral configuration that provides parallel angular momentum and spin components, one can trigger the strength of the SOC phenomena in photonic or plasmonic crystals. Herein, we explore the SOC in a plasmonic crystal, both theoretically and experimentally. Cathodoluminescence (CL) spectroscopy combined with the numerically calculated photonic band structure reveals an energy band splitting that is ascribed to the peculiar spin–orbit interaction of light in the proposed plasmonic crystal. Moreover, we exploit angle-resolved CL and dark-field polarimetry to demonstrate circular-polarization-dependent scattering of surface plasmon waves interacting with the plasmonic crystal. This further confirms that the scattering direction of a given polarization is determined by the transverse spin angular momentum inherently carried by the SP wave, which is in turn locked to the direction of SP propagation. We further propose an interaction Hamiltonian based on axion electrodynamics that underpins the degeneracy breaking of the surface plasmons due to the spin–orbit interaction of light. Our study gives insight into the design of novel plasmonic devices with polarization-dependent directionality of the Bloch plasmons. We expect spin–orbit interactions in plasmonics will find much more scientific interests and potential applications with the continuous development of nanofabrication methodologies and uncovering new aspects of spin–orbit interactions.

中文翻译：

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定点阴极发光光谱探测等离子体晶体中的自旋轨道相互作用

光的自旋-轨道耦合 (SOC) 研究对于探索亚波长结构中的光-物质相互作用至关重要。通过设计具有提供平行角动量和自旋分量的手性配置的等离子体晶格，可以触发光子或等离子体晶体中 SOC 现象的强度。在此，我们从理论上和实验上探索了等离子体晶体中的 SOC。阴极发光 (CL) 光谱与数值计算的光子能带结构相结合揭示了能带分裂，这归因于所提出的等离子体晶体中光的特殊自旋轨道相互作用。此外，我们利用角分辨 CL 和暗场偏振法来证明与等离子体晶体相互作用的表面等离子体激元波的圆偏振相关散射。这进一步证实了给定偏振的散射方向由 SP 波固有的横向自旋角动量决定，而 SP 波又被锁定到 SP 传播的方向。我们进一步提出了一种基于轴子电动力学的相互作用哈密顿量，该哈密顿量支持由于光的自旋轨道相互作用而导致的表面等离子体激元的简并破坏。我们的研究深入了解了具有布洛赫等离子体激元偏振相关方向性的新型等离子体器件的设计。我们预计，随着纳米制造方法的不断发展和自旋轨道相互作用的新方面的发现，等离激元学中的自旋轨道相互作用将发现更多的科学兴趣和潜在应用。