Polar-Topology-Mediated Phonons in Ferroelectric Superlattices

Ferroelectric PbTiO3/SrTiO3 superlattices host diverse polar domain configurations including flux-closures, vortices, skyrmions, and merons at the nanoscale. While sub-THz "vortexon" phonon modes have been observed in the vortex phase, the broader influence of polarization topology on phonon behavior remains unexplored. In this work, we combine monochromated scanning transmission electron microscopy and electron energy-loss spectroscopy (STEM-EELS) with machine-learning molecular dynamics (MLMD) to investigate the full vibrational spectrum of topological polarization structures. By integrating MLMD with multislice simulations, we overcome density-functional-theory scale limitations to model experimental spectra at previously intractable dimensions. Analysis reveals significant modifications to both acoustic and optical phonons, including spatially dependent phonon softening and the emergence of new modes specific to vortex topological structures. Notably, we discover a distinct dichroic phonon response that correlates directly with vortex handedness, demonstrating an intricate coupling between structural topology and vibrational dynamics. This work not only deepens our understanding of structure-property relationships in ferroelectric superlattices but also suggests new pathways for phononic device engineering through polarization texture control.