Surface plasmon polaritons (SPPs) carry transverse optical spin within the evanescent field, which has enabled the demonstration of various chiral light–matter interactions in classical and quantum systems. To achieve high spin selectivity in the interactions, the elliptical polarization of the evanescent field should be made circular, but the engineering principle of the degree of circular polarization (DOCP) of SPPs has been lacking. In this study, we theoretically and numerically investigate the scaling behavior of the DOCP of the SPP field with respect to the modal effective refractive index (n_eff). The DOCP of the SPP field exhibits power-law scalability to the effective refractive index in the one-dimensional (1D) layered system regardless of the material, structural geometry, and excitation wavelength. The power-law scalability is also confirmed in two-dimensional (2D) waveguide structures for in-plane and out-of-plane SPP fields, but the scaling exponents vary depending on the distance from the waveguide boundaries by the reduced symmetry of the given system. Due to Lorentz reciprocity, the power-law scalability can be extended to the coupling directionality of chiral emitters toward the plasmonic waveguide. To this end, we propose a chiral photonic platform for enhanced light–valley interaction, which utilizes simultaneous enhancement of the DOCP and coupling directionality. An incident SPP can excite a chiral emitter with high spin selectivity that unidirectionally couples the emitted light into the plasmonic waveguide, depending on the valley polarization of excitons in 2D materials. Our work provides a ground rule for designing chiral nanophotonic systems and paves the way for the exploration of scale-free phenomena of electromagnetic waves.

中文翻译：

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表面等离子体激元圆偏振度的标度行为


表面等离子体激元（SPP）在倏逝场内携带横向光学自旋，这使得能够在经典和量子系统中演示各种手性光与物质相互作用。为了在相互作用中实现高自旋选择性，倏逝场的椭圆偏振应该是圆形的，但SPP的圆偏振度（DOCP）的工程原理一直缺乏。在本研究中，我们从理论上和数值上研究了 SPP 场的 DOCP 相对于模态有效折射率 (n _eff ) 的标度行为。无论材料、结构几何形状和激发波长如何，SPP 场的 DOCP 对一维 (1D) 层状系统中的有效折射率都表现出幂律可扩展性。幂律可扩展性在面内和面外 SPP 场的二维 (2D) 波导结构中也得到了证实，但由于给定的对称性降低，缩放指数根据距波导边界的距离而变化。系统。由于洛伦兹互易性，幂律可扩展性可以扩展到手性发射器朝向等离子体波导的耦合方向性。为此，我们提出了一种用于增强光谷相互作用的手性光子平台，该平台利用了 DOCP 和耦合方向性的同时增强。入射 SPP 可以激发具有高自旋选择性的手性发射器，根据 2D 材料中激子的谷偏振，将发射的光单向耦合到等离子体波导中。我们的工作为设计手性纳米光子系统提供了基本规则，并为探索电磁波的无标度现象铺平了道路。