Skyrmionium-like ring-domain polar textures in wrinkled freestanding bilayer BaTiO 3 nanomembranes

Freestanding ferroelectric nanomembranes provide a useful platform for exploring polar states coupled to mechanical deformation. Here, we report wrinkled freestanding bilayer BaTiO 3 nanomembranes in which bubble-like bulges formed after release and transfer are accompanied by pronounced concentric ring-domain piezoresponse features. Angle-resolved piezoresponse force microscopy (PFM) suggests an approximately radial in-plane organization together with ring-like modulation of the out-of-plane contrast, consistent with a skyrmionium-like ring-domain polar texture. Compared with the single-layer regions examined here, bilayer membranes exhibit more distinct wrinkle-associated ring-domain features, indicating an important role of layer stacking and deformation geometry. Phase-field simulations further support contributions from wrinkle-induced strain gradients and associated flexoelectric effects to the formation and stabilization of the observed texture. In addition, local electric bias modifies the characteristic size of the inner domain under the tested conditions, indicating electrical tunability of the ring-domain configuration. These results suggest that wrinkled freestanding ferroelectric nanomembranes provide a useful platform for accessing mechanically coupled ring-domain polar textures and reconfigurable ferroelectric functionalities.