Data underlying the publication and chapter 3: Breakdown of spin-to-helicity locking at the nanoscale in topological photonic crystal edge states

We measure the local near-field spin in topological edge state waveguides that emulate the quantum spin Hall effect. We reveal a highly structured spin density distribution that is not linked to a unique pseudospin value. From experimental near-field real-space maps and numerical calculations, we confirm that this local structure is essential in understanding the properties of optical edge states and light-matter interactions. The global spin is reduced by a factor of 30 in the near field and, for certain frequencies, flipped compared to the pseudospin measured in the far field. We experimentally reveal the influence of higher-order Bloch harmonics in spin inhomogeneity, leading to a breakdown in the coupling between local helicity and global spin.

我们针对模拟量子自旋霍尔效应（quantum spin Hall effect）的拓扑边缘态波导（topological edge state waveguides），对其局域近场自旋展开了测量。我们观测到一种高度结构化的自旋密度分布，该分布并不对应唯一的赝自旋（pseudospin）取值。结合实验近场实空间成像（near-field real-space maps）与数值计算结果，我们证实该局域结构对于理解光学边缘态（optical edge states）与光-物质相互作用（light-matter interactions）的特性至关重要。近场环境下的整体自旋幅值相较于远场测得的赝自旋降低了30倍，且在特定频率下发生了自旋翻转。我们通过实验揭示了高阶布洛赫谐波（higher-order Bloch harmonics）对自旋不均匀性（spin inhomogeneity）的影响，该效应会打破局部手征性（local helicity）与整体自旋之间的耦合关系。