Strain Engineering of Polar Topological Phases From Atomic Simulations

Polar topological structures have attracted significant attention due to their rich physical properties and promising potential for next-generation nanoelectronics. The control and manipulation of polar topological textures have emerged as a challenge for their implementation in devices. Here, using a first-principles-based active-learning effective Hamiltonian approach, topologically nontrivial and trivial domain configurations in PbTiO3 thin films are systematically investigated. Under tensile epitaxial strain, vortex-antivortex, in-plane a1/a2-like, and single-domain states exhibit comparable energies and can coexist. At low compressive strain, the system stabilizes vortex-tube array domains. Under high compressive strain, a sequence of topologically nontrivial phases is observed, evolving from skyrmions to mixed skyrmion-skyrmionium states and ultimately to skyrmioniums with increasing strain amplitude. These topological textures are robust and remain stable under small-to-moderate electric fields, but eventually transform into trivial domains under stronger fields. Furthermore, a strain-driven reversible transition between skyrmions and skyrmioniums is identified, revealing a domain nucleation and growth pathway in the phase transition. These findings elucidate the formation and evolution of topological polar structures in ferroelectric thin films and highlight strain engineering as an effective strategy for manipulating polar textures, offering new opportunities for future nanoelectronic devices.