Chiral soft mode transition driven by strain in ferroelectric bubble domains

TL;DR

This study demonstrates a strain-induced achiral-to-chiral phase transition in ferroelectric bubble domains, revealing soft chiral phonon modes and a topological change, thus establishing chirality as a ferroic order.

Contribution

It provides the first clear example of a soft-mode achiral-to-chiral transition driven by strain in a solid-state system, with detailed simulation evidence.

Findings

Identification of chiral phonon modes softening under strain

Observation of a topological change accompanying the transition

Establishment of chirality as a ferroic order in solids

Abstract

Chirality in solids is attracting growing attention as a potential ferroic order, yet virtually no paradigmatic example of a soft-mode achiral-to-chiral phase transition has been firmly established to date. Here we identify ferroelectric bubble domains as a model system that undergoes a strain-driven achiral-to-chiral transition exhibiting the hallmarks of spontaneous symmetry breaking. Using second-principles atomistic simulations, we uncover chiral phonon modes in ferroelectric/dielectric superlattices that soften under epitaxial strain following textbook soft-mode behaviour. The transition is accompanied by a change in topological character, highlighting an interplay between chirality and topology in these systems. This work provides a concrete step towards establishing chirality as a genuine ferroic order in solids.