Korea Advanced Institute of Science and Technology (KAIST)

Abstract

Recent advances in electron microscopy now allow us to directly visualize complex structural phenomena and exotic orderings in materials at the single-atom level. In this talk, I will introduce the fundamental principles of atomic electron tomography (AET), a technique capable of determining the full 3D atomic structure of individual nanoparticles without crystallographic averaging. I will present our recent work on visualizing three-dimensional topological polar ordering in ferroelectric nanoparticles, providing direct atomic-scale evidence of exotic polar textures relevant to topology and functional control in oxides—purely originating from surface boundary conditions, without the need for epitaxial strain.

I will further introduce a complementary momentum-resolved technique, 4D-STEM, performed under cryogenic conditions using a liquid helium holder. This approach enables spatial mapping of charge density wave (CDW) correlations across the phase transition in 2H-NbSe2. I will discuss how the evolution of CDW correlation length reveals critical-like behavior near the transition temperature, opening new pathways for probing phase transitions in low-dimensional quantum materials.

Brief Bio

Dr Yongsoo Yang is a researcher in the Department of Physics at the Korea Advanced Institute of Science and Technology (KAIST). He earned his Ph.D. in Physics from the University of Michigan, where he focused on synchrotron X-ray scattering to investigate atomic structures at surfaces and interfaces in oxide systems. During his postdoctoral research at UCLA, he expanded into electron optics and pioneered atomic electron tomography, a technique enabling three-dimensional structural determination of nanomaterials at the single-atom level. At KAIST, his research centers on advancing multi-dimensional electron imaging, with particular emphasis on precise 3D mapping of atomic arrangements at surfaces and interfaces, and the atomic-scale characterization of complex topological order.

联系人：陈震 zhen.chen@iphy.ac.cn 010-82649878

邀请人：陈震 特聘研究员