Designing dislocation-driven polar vortex networks in twisted perovskites

TL;DR

This study reveals that twisting freestanding SrTiO3 layers creates ordered dislocation networks linked to in-plane topological vortices, enabling new control over local polar and electronic structures in oxide materials.

Contribution

It demonstrates that twist-induced dislocation networks in SrTiO3 generate topological vortices, distinct from moire patterns, and uses advanced microscopy and modeling to understand this phenomenon.

Findings

Dislocation networks in twisted SrTiO3 are associated with in-plane topological vortices.

Vortex-antivortex arrays exhibit long-range order with continuous polarization rotation.

Strain competition within dislocation networks stabilizes polar vortex-antivortex pairs.

Abstract

Twisting two atomic layers produces a geometric moire pattern, but bonding-induced interfacial reconstruction fundamentally transforms this into an ordered dislocation network - a distinction obscured in weakly-bonded van der Waals systems. Although in-plane topological vortex nanostructures arising from twisting-induced lateral strain modulation have been linked to periodic moire patterns in freestanding perovskite layers and 2D bilayers, their coupling to the interfacial dislocation network in twisted layers remains unresolved. Here we demonstrate that twisting freestanding SrTiO3 layers undergo interfacial reconstruction into a network of screw dislocations, accompanied by the emergence of in-plane topological vortices. Unlike in previous reports, these vortices are associated with the periodicity of the dislocation network rather than with geometric moire patterns. Four-dimensional scanning transmission electron microscopy (4D-STEM) reveals long-range ordered vortex-antivortex arrays with nearly continuous polarisation rotation. A machine-learning interatomic potential, trained on first-principles calculations, together with phase-field modelling, confirms that competing strains within the dislocation network stabilize polar vortex-antivortex pairs and drive the emergence of an electronic superlattice with a well-defined periodicity. Our results establish twist-controlled dislocation networks as a new and versatile route to designing local polar and electronic structures in oxide materials.