Atomic-Scale Tracking Phase Transition Dynamics of Berezinskii-Kosterlitz-Thouless Polar Vortex-Antivortex

TL;DR

This study visualizes the atomic-scale dynamics of vortex-antivortex pairs during phase transitions, revealing their behaviors under thermal and electrical stimuli, challenging the traditional BKT transition model, and offering insights for electronic applications.

Contribution

It provides the first atomic-resolution observation of V-AV pair dynamics during phase transitions, using in situ electron microscopy and simulations, and clarifies their behaviors beyond the BKT theory.

Findings

No BKT phase transition observed at atomic scale.

Polarization suppression occurs with increasing temperature.

Electric fields induce vortex-antivortex annihilation.

Abstract

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.