Domain-Pair Intertwined Topological Domain Structure in Elemental Bi Monolayer

TL;DR

This study reveals a novel topological multi-domain structure in Bi monolayer with charge-reversal polarization switching at domain walls, offering new insights for nano-electronic applications.

Contribution

It uncovers a unique intertwined topological domain structure and polarization switching mechanism in Bi monolayer, challenging conventional understanding of charge-neutral domain walls.

Findings

Discovered a polarization reversal mechanism via atomic shuffle without bond breaking.

Identified a stable multi-domain topological structure under strain.

Revealed charge-reversal at 180° domain walls affecting domain topology.

Abstract

Ferroelectric domain structures, separated by domain walls, often display unconventional physics and hold significant potential for applications in nano-devices. Most naturally growth domain walls are charge-neutral to avoid increased electrostatic energy, while the intrinsically stable charged 180{\deg} domain walls in Bi monolayer challenged this conventional knowledge and emerged an unexplored field. Here, using machine-learning potential and molecular dynamics (MD) simulations, we investigated the finite-temperature dynamics of domain walls and discovered a domain-pair intertwined topological domain structure in Bi monolayer. In 180{\deg} domain walls, a unique polarization switching mechanism is observed, characterized by the out-of-plane shuffle of Bi atoms without bond breaking. This shuffle mechanism reverses the charge properties of Bi atoms, transforming Bi anions into cations and vice versa, ultimately reversing the polarization. Then, we observed a topological multi-domain structure with two groups of domain pairs intertwined. The charged 180{\deg} domain walls form local domain pairs, with the 90{\deg} domain walls emerge between different domain pairs. This multi-domain maintains a stable topological structure within the strain range ({\epsilon}_x = 0 to 4.70%) and exhibits rich domain wall reactions under further applied strain. Our findings provide insights into the charged 180{\deg} domain walls and the related topological domain structures, enabling new opportunities for applications in electronic and nano-electronic devices.