Domain-Pair Intertwined Topological Domain Structures in Elemental Bi Monolayer

Ferroelectric domain walls play a fundamental role in the functionality of ferroelectric materials. As ferroelectric domain walls are mostly charge neutral to minimize electrostatic energy, the recently observed intrinsically stable charged 180° domain wall in a Bi monolayer opens uncharted research territory. In this Letter, we utilized deep potential molecular dynamics (DeePMD) simulations to investigate the finite-temperature dynamics of domain walls in the Bi monolayer. We discovered unique intertwined topological domain structures formed by two domain pairs (created by the charged 180° domain walls) separated by conventional 90° domain walls. These topological domain wall structures exhibit complex reaction dynamics when subjected to mechanical loading. They retain their structural topology up to a tensile strain of 4.70%. Beyond this strain, they begin to merge, cross, and ultimately transform into an identical counterpart, rotated by 90°. At strain exceeding 9%, the topological structure disintegrates into parallel charged 180° domain walls. Our findings provide unprecedented insights into the topological structures of charged 180° domain walls, laying the groundwork for further investigations and potential applications in electronic devices.