Mid-IR Phononic Excitation Driven Collective Dynamics in Polar Superlattice

Topological polar textures in oxide superlattices exhibit emergent electronic properties and sub-terahertz collective dynamics, offering a pathway for ultrafast control of ferroelectric order. However, the direct excitation and control of these modes remains a significant challenge. We present experimental evidence of driven collective modes in an a1/a2 domain superlattice via intense mid-infrared pulse exciation. The observed nonlinear phononic rectification and its pump-field dependence directly demonstrate a nonlinear coupling between lattice vibrations and the collective polar mode. This mechanism is validated by phase-field simulations and density functional theory, which qualitatively reproduces the key features observed in the experiment. Crucially, measurements on polar skyrmion lattices show no excitation of sub-terahertz collective mode in absence of non-linear phononic rectification, confirming the specificity of this excitation pathway. These results render nonlinear phononics a viable, adjustable mechanism for optically exciting and controlling polar collective modes, enabling dynamic control over complex ferroelectric textures and their operational behaviors.