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.

我们在模拟量子自旋霍尔效应（quantum spin Hall effect）的拓扑边缘态波导中，开展局域近场自旋的测量。我们观测到一种高度结构化的自旋密度分布，该分布与单一赝自旋（pseudospin）数值并无对应关联。结合实验近场实空间图谱与数值计算结果，我们证实该局域结构对于理解光学边缘态（optical edge states）以及光与物质相互作用（light-matter interactions）的物理特性至关重要。近场条件下的全局自旋幅值被压缩至远场测得赝自旋的1/30，且在特定频率下与远场赝自旋相比发生翻转。我们通过实验揭示了高阶布洛赫谐波（Bloch harmonics）对自旋不均匀性的影响，该效应会破坏局域螺旋度（helicity）与全局自旋之间的耦合关系。