  Particle-like topologies, such as vortex-antivortex (V-AV) pairs, have
garnered significant attention in the field of condensed matter. However, the
detailed phase transition dynamics of V-AV pairs, as exemplified by
self-annihilation, motion, and dissociation, have yet to be verified in real
space due to the lack of suitable experimental techniques. Here, we employ
polar V-AV pairs as a model system and track their transition pathways at
atomic resolution with the aid of in situ (scanning) transmission electron
microscopy and phase field simulations. We demonstrate the absence of a
Berezinskii-Kosterlitz-Thouless phase transition between the room-temperature
quasi-long-range ordered ground phase and the high-temperature disordered
phase. Instead, we observe polarization suppression in bound V-AV pairs as the
temperature increases. Furthermore, electric fields can promote the vortex and
antivortex to approach each other and annihilate near the interface. The
elucidated intermediate dynamic behaviors of polar V-AV pairs under thermal-
and electrical-fields lay the foundation for their potential applications in
electronic devices. Moreover, the dynamic behaviors revealed at atomic scale
provide us new insights into understanding topological phase of matter and
their topological phase transitions.

Applied Physics;Materials Science