Exploring Non-Equilibrium Ferroelectric Phases through Twisted Light Matter-Interaction
The dynamic control of novel ordered states of matter, particularly those unattainable in thermodynamic equilibrium, remains a cornerstone of condensed matter physics. Recent advancements have demonstrated that intense terahertz (THz) fields can induce significant phenomena such as metal-insulator transitions, superconductivity, and ferroelectricity in quantum para electrics, as well as room temperature magnetization through circularly polarized THz electric fields. Central to these phenomena is the excitation of infrared-active soft phonon modes by THz electric fields, which facilitates the manipulation of material properties. Extending this paradigm, recent theoretical work suggests that ferroelectric polarization can be dynamically manipulated using twisted light carrying orbital angular momentum (OAM) to induce ferroelectric skyrmions.
In this talk, I will present our latest experimental evidence demonstrating that such control is achievable in the quasi-2D ferroelectric CsBiNb2O7 using twisted ultraviolet (UV) light carrying OAM. Unlike THz light, where the interaction is resonant with soft phonon modes, twisted UV light operates in a non-resonant regime. The high-frequency electric field oscillations of UV light induce changes in ferroelectric polarization through multiphoton absorption and localized strain effects. These interactions leverage mid-gap states and defect-mediated pathways to couple OAM to ionic displacements and polarization textures. Twisted UV light imparts quasi-static strain gradients, enabling dynamic modulation of ferroelectric domains and topological structures such as Bloch points and vortex-antivortex pairs. We develop and employ in-situ X-ray Bragg coherent diffractive imaging, twisted optical Raman spectroscopy, and density functional theory calculations to spatially resolve in three dimensions the resulting lattice distortions and changes in ferroelectric polarization textures. Our observations revealdeterministic and reversible twisted light-induced strain and atomic displacements within the unit cell, leading to significant microscopic changes in ferroelectric polarization. These changes result from the time-averaged effects of twisted UV light interacting with mid-gap states, phonon modes, and strain gradients, highlighting a novel mechanism for non-resonant light-matter interaction. This mechanism drives the stabilization of non-equilibrium ferroelectric phases that harbor topological solitons far from thermodynamic equilibrium. These findings open new paths for controlling ferroelectricity, magnetism, and collective excitations in correlated materials based on van der Waals heterostructures.