Flexoelectric-stabilized hierarchical polar bubbles in wrinkled ferroelectric CuInP2S6

Abstract

The realization of complex, high-order topological textures in ferroelectrics typically relies on demanding epitaxial growth under substrate clamping. Here, we report hierarchical polar bubbles in the van der Waals ferroelectric CuInP2S6, enabled by a facile wrinkle-induced strain-engineering strategy. Vector piezoresponse force microscopy reveals that localized wrinkled bulges generate large strain gradients, which activate a flexoelectric-assisted polarization reversal and form a macroscopic polar envelope. This macro-bubble encapsulates pre-existing intrinsic ferroelectric nanodomains, resulting in a distinctive nested bubble-in-a-bubble hierarchical architecture. Statistical analysis indicates that the formation probability decreases with increasing flake thickness, providing strong evidence for a strain-gradient-dominated flexoelectric origin. Real-time in situ manipulation demonstrates the mechanical recoverability of these hierarchical states under external loading. This work introduces a novel form of ferroelectric topology and establishes a mechanical pathway for designing resilient functional elements for next-generation straintronic devices.