Polar Vortex Domain Walls Dynamics Directly Imaged using Ultrafast Electron Microscopy

Understanding domain wall motion is crucial for advancing ferroelectric (FE)-based applications. However, in conventional FEs, such studies are often obscured due to the prevalent atomic disorder that strongly pins domain walls. Recent discoveries of quasi-long-range ordered topological polar textures, such as polar vortices and skyrmions in oxide superlattices, provide an alternative platform to probe domain wall dynamics. Here, we investigate domain wall dynamics in PbTiO3/SrTiO3 superlattices using ultrafast electron diffraction and microscopy. Upon photoexcitation, we observe asymmetric domain melting occurring within ~1 ps, followed by the growth of the surviving domain into the region of the melted one. This process reveals domain wall velocities on the order of 100 m/s, comparable to the speed of sound. These results indicate that polar nanotextures (∼10 nm scale) are less affected by atomic scale defects, enabling access to the intrinsic domain wall motion in FEs. Our findings shed new light on the fundamental velocity limit of FE domain wall motion and open pathways for engineering next-generation ferroelectric memory devices.