MSE Seminar Series: Polarization Textures: Beyond Ferroelectrics

Speaker

Jayakanth Ravichandran, Associate Professor, University of Southern California, Los Angeles

Abstract

Topological defects such as vortices and skyrmions have recently gained significant interest in solid state materials as ferroic materials (ferromagnets and ferroelectrics) have become a test bed to realize and control these nanoscale structures. Although this phenomenon is being investigated as a pathway to energy efficient information storage, broader applications in interaction of electromagnetic waves with such features are emerging. In the case of ferroelectrics, boundary condition engineering is used to achieve vortices, skyrmions, and merons in low dimensional epitaxial oxide heterostructures.

In this talk, I will introduce the notion that similar phenomenology but at the atomic scale can be achieved in charge density wave phases, especially nominally semiconducting chalcogenides. I will outline my group and other groups efforts in showing non-trivial toroidal polar topologies at the atomic level in chalcogenides with nominally empty conduction band with d-orbital character such as 1T-TiSe₂, Ta₂NiSe₅ and BaTiS₃. Specifically, we use X-ray single crystal diffraction as a probe for high quality single crystals of a quasi-1D hexagonal chalcogenide, BaTiS₃, to reveal complex polar topologies such as vortices, and head-to-head and tail-to-tail arrangement of dipoles. Recent experiments and theoretical studies on the stability and dynamics of these features will also be discussed. Lastly, I will outline how such platforms can broadly enable the search for materials with chiral optical materials and polarization sensitive light-matter interaction.    

Biography

Jayakanth Ravichandran is an Associate Professor in the Mork Family Department of Chemical Engineering and Materials Science with a courtesy appointment in the Ming Hsieh Department of Electrical and Computer Engineering at the University of Southern California. He holds the Philip and Cayley MacDonald endowed early career chair. He serves as a co-director of the Core Center of Excellence in Nano Imaging (CNI) and as the PI of the Army Research Office MURI program. He received his Ph.D. degree from the University of California, Berkeley, in 2011. He performed post-doctoral research at Columbia University and briefly at Harvard University before joining USC in 2015 as an Assistant Professor. His research interests are in materials design, synthesis, characterization, and the physical properties of complex materials for electronic, photonic, and energy applications. His honors include the 2020 TMS Young Leader Professional Development Award and the 2017 Early Career Scholar in Materials Science by the Journal of Materials Research.