Goldstone-Mediated Polar Instability in Hexagonal Barium Titanate

We discover a rare structural manifestation of the Goldstone paradigm in a hexagonal polytype of the prototypical ferroelectric BaTiO_{3}. First-principles calculations confirm the Goldstone character of the order parameter, while our high-resolution diffraction measurements unveil an unusual reentrant Goldstone regime manifesting as a quasicontinuous domain texture in the vicinity of the ferroelectric transition. We develop a minimal Landau model that encapsulates these observations, illustrating how U(1) symmetry can be restored at the ferroelectric transition. Our findings demonstrate how exotic Goldstone physics can be unlocked in systems dominated by highly anharmonic interactions, presenting a promising pathway to stabilize emergent polar topologies in bulk materials.