Fig. 2: Polar vortex–antivortex pairs in designed (PTO)n/(STO)m superlattice.
From: Creating polar antivortex in PbTiO3/SrTiO3 superlattice
a A low-magnification HAADF image depicts STO layers with varying thicknesses (4, 7, 10, and 15 u.c.) sandwiched between 10-u.c. PTO layers. b Dark field TEM image under two-beam conditions by selecting (002)pc g vector (subscript pc denotes pseudocubic). The periodic array of bright and dark intensity modulation corresponds to vortex arrays within PTO layers. c The spatial distribution of the out-of-plane polarization (unit: μC/cm2) was calculated from phase-field simulation. Inset: enlarged view of the polar vector configuration (black arrows). d An atomically resolved HAADF image for a 4-u.c. thick STO sandwiched between adjacent 10-u.c. PTO layers, colored for clarity. e Map of polar vectors between cations extracted from the HAADF image depicts vortex–antivortex texture. The cores of antivortices are highlighted by the dotted diamond boxes. Enlarged views of polar vectors overlaid with polar angle variation taken from dashed highlighted rectangle boxes in e for antivortex (red color) in STO (f) and vortex (black color) in PTO (g), respectively. Variation of polar displacement components within antivortex structure along A–B (h) and C–D (i) directions, as marked in e. Dx represents in-plane displacement and Dz represents out-of-plane displacement.
