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

Abstract

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.