Mechanically liberating polarization bubbles in van der Waals ferroelectrics.

Ferroelectric topological textures have sparked intensive interest, due to their exciting applications in a new era of non-volatile and ultrahigh-density information storage. However, these textures remain largely dependent on the given heterostructures with engineered neighbouring layers to balance the competing energies. Here we report high-density polarization bubbles in van der Waals ferroelectric crystals CuInP2S6, without the need for a spatially confined heterostructure. From piezoresponse force microscopy, it is observed that the formation and distribution of bubble domains exist in the inherent coexistence of polar phases. Crucially, the phase ratio can be facilely tailored by external stimuli such as mechanical force, enabling the labyrinth domains to be manipulated into high-density isolated bubbles through a mechanism involving polar phase competition and flexoelectricity, as revealed through density functional theory and phase-field modelling. Our findings not only provide insights into the creation of topological structures in a controlled manner but also demonstrate potential memory applications based on bubble domains in van der Waals ferroelectrics.