Giant refraction and enhanced nonlinear optical response in KTN:Li ferroelectric supercrystals

Ferroelectric domain patterns have attracted wide-spread attention both as a means to understand how topology emerges spontaneously during a transition and as a platform for nonlinear optics applications. We discuss recent experiments that have revealed how the 3-axis broken-inversion-symmetry transition associated to the ferroelectric transition in lithium-enriched potassium-tantalate-niobate leads to 3D periodic lattices of high-dimensional spontaneous polarization topological defects. These supercrystals scatter light like xray diffraction and manifest giant refractive properties. The result is sample with remarkable optical properties, such as constraint-free wavelength conversion and achromatic light transmission, phenomena whose theoretical understanding is still in the making.