Fig. 3: Characterization of the limit polar skyrmion.
From: Absence of critical thickness for polar skyrmions with breaking the Kittel’s law
a Planar-view DF under-focus STEM imaging of (PTO4/STO4)10 superlattices, showing the widespread occurrence of rounded polar skyrmions. The individual skyrmion is marked by white dotted circle. The 3D skyrmion maps are located under the under-focus STEM images. b Atomically resolved cross-sectional HAADF-STEM images of (PTO2/STO2)10 superlattices. The yellow and red circles denote the Pb and Ti atom columns, respectively, and the red arrow denotes the direction of Ti-displacement (δTi) vectors. c The reversed δTi vector maps (spontaneous polarization, Ps), revealing the thickness-dependent skyrmion. d The shift Y along the out-of-plane direction. e–g The first-principles calculation result of a PTO2/STO2 superlattice containing a skyrmion. e The three-dimensional presentation of the polarization vectors. f The top view of the polarization vectors of the PTO layer showing the vortex-antivortex pattern. g The cross-sectional view of the polarization vectors of the front layer in e. The polarization vectors with positive Pz components are colored by their in-plane directions and those with negative Pz components are in the gray (or white) color. The spacing between vectors is one unit cell.
