Emergent Atomistic Polarization Textures in Quasi-1D Hexagonal Chalcogenides

The realization of topological defects such as vortices and skyrmions in magnetic and dipolar systems has allowed us to test their stability and dynamics at the microscopic limit, and also reimagine electronic and photonic functionalities in “ferroic” materials. In the case of vortex-antivortex structures, both magnetic and dipolar systems rely on boundary condition engineering and hence, their stability is dictated by narrow geometric conditions in nanoscale structures. In this talk, I will report the existence of atomic-scale vortex-antivortex dipolar structures in a quasi-1D hexagonal chalcogenide, BaTiS₃ from the refined structures of X-ray synchrotron single crystal diffraction studies. BaTiS₃ undergoes a series of electronic transitions from a room temperature ferrielectric phase to a vortex phase with the vortex-antivortex dipolar structures below ~250 K through a second order phase transition, and then, transforms into a lower symmetry phase below 180 K. In the vortex phase, we observe large displacements of Ti in the TiS₆ octahedra of BaTiS₃, comparable to ferroelectric perovskite oxides, along c-axis and in a-b plane suggesting the robustness of the polar textures. Electrical transport studies show that these phase transitions are sensitive to strain, and hence, one can infer the tunability of the electronic properties of the vortex phase. We presume the role of multipole interactions as the origin of these emergent polarization textures and note similarities in structure and electrical characteristics with charge density wave materials such as 1T-TiSe₂ and Ta₂NiSe₅. Our work setups up complex charge density waves with d⁰ filling as a playground for realizing and understanding quantum polarization topologies.