Mechanical configurable nanopatterning of polar topological states and formation of post-skyrmion

TL;DR

This study demonstrates how mechanical stress can controllably manipulate polar topological states, like skyrmions, in ferroelectric materials, enabling nanopatterning for future nanoelectronic applications.

Contribution

It introduces a novel mechanical nanopatterning method for polar skyrmions in ferroelectric superlattices using AFM tip-induced stress, revealing new topological structures.

Findings

Skyrmions coalesce into stripes under small to moderate stress.

Higher stress suppresses polarization, creating post-skyrmion structures.

Mechanical nanopatterning can be reversed with electric fields.

Abstract

The controllable phase transition and nanopatterning of topological states in a ferroelectric system under external stimuli are critical for realizing the potential applications in nanoelectronic devices such as logic, memory, race-track, etc. Herein, using the phase-field simulations, we demonstrate the mechanical manipulation of polar skyrmions in ferroelectric superlattices by applying external local compressive stress through an atomic force microscopy (AFM) tip. Different switching pathways are observed: under small to moderate force (<1 uN), the skyrmions coalesce to form a long stripe; while increasing the applied load (e.g., above 2 uN) leads to the suppression of spontaneous polarization, forming a new metastable topological structure, namely the post-skyrmion. It is constructed by attaching multiple merons onto a center Bloch skyrmion, showing a topological charge of 1.5 (under 2 uN) or 2 (under 3 uN). We have further designed a mechanical nanopatterning process, where the stripes can form a designed pattern by moving the AFM tip (write), which can also be switched back to a full skyrmion state under an applied electric field (erase). We believe this study will spur further interest in mechanical manipulation and nanopatterning of polar topological phases through mechanical forces.