  Topological polar vortices that are the electric analogues of magnetic
objects, present great potential in applications of future nanoelectronics due
to their nanometer size, anomalous dielectric response, and chirality. To
enable the functionalities, it is prerequisite to manipulate the polar states
and chirality by using external stimuli. Here, we probe the evolutions of polar
state and chirality of polar vortices in PbTiO3/SrTiO3 superlattices under
electric field by using atomically resolved in situ scanning transmission
electron microscopy and phase-field simulations. We find that the adjacent
clockwise and counterclockwise vortex usually have opposite chirality. The
phase-field simulations suggest that the rotation reversal or axial
polarization switching can lead to the chirality change. Guided by which, we
experimentally validate that the vortex rotation direction can be changed by
applying and subsequently removing of electric fields, offering a potential
strategy to manipulate the vortex chirality. The revealed details of dynamic
behavior for individual polar vortices at atomic scale and the proposed
strategy for chirality manipulation provide fundamentals for future device
applications.
