Polar Textures in Complex Chalcogenides

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, and their broad connection to low dimensional magnets will also be discussed. Lastly, I will outline the perspective for photonic applications of polarization textures.