Shedding Light On Non-Ising Polar Domain Walls: Insight From Second Harmonic Generation Microscopy And Polarimetry Analysis

Polar domain walls are currently at the focus of intensive research owing to their unusual and highly localized functional properties, which bear great potential for technological applications. They can present unusual topological features, like swirling polar structures or defect lines. The prediction of possible non-Ising and chiral internal structures of polar domain walls has been a particularly important development in this topic over the past years. This Tutorial highlights the capabilities of non-linear optics to probe these newly discovered aspects in polar non-Ising type domain walls through the second-harmonic generation (SHG) process. Fundamental symmetry properties of domain walls are presented in the context of recent advances on chiral and abnormal polar structures. We introduce the basics of the SHG and its ability to probe the symmetry down to the nanoscale, and we explain how to obtain insight into the non-Ising character of polar domain walls by combining the SHG polarimetry analysis with modeling.