Invited (remote)
Probing properties and dynamic behaviors of topological polar states by 4D STEM

Topological polar solitions such as domain walls, polar voritices, skyrmions, etc, in ferroelectrics have attracted much attention owing to their unique functionalities and potential applications in electronic devices. Recent advances in transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) provides powerful tools to study the structure, properties, and dynamic behaviors of nanostructures with atomic resolution. In this talk, I will show how ferroelectric domains nucleate and evolve under applied electric field in TEM. Using quantitative TEM, we can measure and map the electric polarization of nanodomains, vortices and other polar solitons with the atomic resolution. Recently, we have developed a novel four-dimensional STEM (4D STEM) method that can directly map the local electric field and charge density of crystalline materials in real space with sub-angstrom resolution.[1]. I will also show that skyrmion-like polar nanodomains can be created in lead titanate/strontium titanate bilayers transferred onto silicon and can be switched from one type to another by an applied electric field, which substantially modifies their resistive behaviours.[2] The polar-configuration-modulated resistance is ascribed to the distinct band bending and charge carrier distribution in the core of the two types of polar texture. The integration of high-density (more than 200 gigabits per square inch) switchable skyrmion-like polar nanodomains on silicon may enable non-volatile memory applications using topological polar structures in oxides.

[1] W. P. Gao et al., Nature 575, 490 (2019)
[2] L. Han et al., Nature 603, 63 (2022).