Observation of Néel-Skyrmions in Bilayered Oxide Ferroelectrics

Skyrmions in ferromagnetic materials exhibit either Néel or Bloch characteristics. Although skyrmions in ferromagnetic materials can be readily obtained via inter-spin interactions, a skyrmion in ferroelectric materials exhibiting solely Néel or Bloch characteristics has not yet been discovered. Here, by modulating the formation of skyrmion-bubbles in [(PbTiO₃)_n/(SrTiO₃)_n]₁ [(PTO_n/STO_n)₁] bilayers grown on STO substrates, the atomic morphology of pure Néel-skyrmion is observed with a topological charge of ± 1 in the ultrathin bilayered films with the thickness of 2 unit cells (u.c.). Such a pure Néel-skyrmion is confirmed by a combination of atomic mappings, geometric phase analysis, and X-ray 3D reciprocal space mapping (RSM). It is found that decreasing the thickness of bilayered films from 50 to 2 u.c., the characteristics of skyrmion-bubbles exhibiting both Néel and Bloch features disappear along with the Bloch features. The formation mechanism of the Néel-skyrmions is unveiled using Phase-field simulations, showing the critical role of electric and gradient energy variation in the stable phase of Néel-skyrmions. These nanoscale pure Néel-skyrmions represent the electrical equivalents of their magnetic counterparts, extending the size limits of topological phases and offering potential advancements in the field of ferroelectric physics.