Manipulating Ferroelectric Topological Polar Structures with Twisted Light.

The dynamic control of non-equilibrium states represents a central challenge in condensed matter physics. While intense terahertz fields drive metal-insulator transitions and ferroelectricity via soft phonon modes, recent theory suggests that twisted light with orbital angular momentum (OAM) offers a distinct route to manipulate ferroelectric order and stabilize topological excitations including skyrmions, vortices, and Hopfions. Control of ferroelectric polarization in quasi-2D CsBiNb₂O₇ (CBNO) is demonstrated using non-resonant twisted ultra-violet (UV) light (375 nm, 800 THz). Combining in situ X-ray Bragg coherent diffractive imaging (BCDI), twisted optical Raman spectroscopy, and density functional theory (DFT), three-dimensional (3D) ionic displacements, strain fields, and polarization changes are resolved in single crystals. Operando measurements reveal light-induced strain hysteresis under twisted light-a hallmark of nonlinear, history-dependent ferroelastic switching driven by OAM. Discrete, irreversible domain transitions emerge as the topological charge ℓ is cycled, stabilizing non-trivial domain textures including vortex-antivortex pairs, Bloch/anti-Bloch points, and merons. These persist after OAM removal, indicating a memory effect. Competing mechanisms are discussed, including multiphoton absorption, strain-mediated polarization switching, and defect-wall interactions. The findings establish structured light as a tool for deterministic, reversible control of ferroic states, enabling optically reconfigurable non-volatile devices.