Scalable and Controllable Flexoelectric Engineering of van der Waals Polar Skyrmion Bubble Arrays.

Nontrivial topological polarization textures, including polar skyrmions, possess nanoscale three-dimensional polarization arrangements that exhibit unique properties and promising applications. Theoretically, these nontrivial polar textures can be created and annihilated by a flexoelectricity effect, but experimental realization, particularly on pure silicon substrates, remains elusive. Here, we show a scalable approach of leveraging silicon patterns to induce flexoelectricity in a van der Waals ferroionic CuInP2S6 crystal. Mediated by copper ion migration, this approach can transform conventional ferroelectric CuInP2S6 domains into polar skyrmions. We controllably manipulate the size of polar skyrmions by adjusting the diameter of silicon nanopatterns and the thickness of the CuInP2S6 samples. Such skyrmionic textures can achieve reversible resistance switching. Phase-field simulations, Raman spectroscopy, and second harmonic generation prove that the transformation to polar skyrmions is associated with flexoelectricity-induced collective interactions between electrostatic, elastic, and gradient energy. Our study provides an avenue for artificially engineering nontrivial polar textures toward silicon-based high-density memory.