Extended Data Fig. 2: Topologically unstable spin merons in three-wave interference.
From: Topological water-wave structures manipulating particles
Shown are: distributions of the unit spin-density vectors \(\bar{{\bf{S}}}(x,y)\), represented by brightness (\({\bar{S}}_{z}\)) and color (\({\tan }^{-1}({\bar{S}}_{y}/{\bar{S}}_{x})\)), the meron boundaries \({S}_{z}=0\) (red curves), and mappings of the unit spin vectors in the merons onto the unit sphere, with the corresponding topological numbers \({Q}_{S}\). a, An ideal theoretically-predicted three-wave interference exhibiting a lattice of triangular alternating merons with \({Q}_{S}=\pm 1/2\). b, Perturbed three-wave interference field observed in our experiment (see Fig. 2). The curves \({S}_{z}=0\) do not form closed meron areas. Closing the gaps with black lines and mapping the unit spin vectors onto the unit sphere results in ‘quasi-merons’ with non-half-integer numbers \({Q}_{S}\).
