Giant piezoelectric effects of topological structures in stretched ferroelectric membranes

TL;DR

This study reveals that strained ferroelectric membranes host topological dipole structures with giant piezoelectric effects, driven by dynamic dipole rotations and novel topological phases, advancing the understanding of ferroelectric topological phenomena.

Contribution

It uncovers a new ferroelectric topological structure called 'dipole spiral' with giant piezoelectric response, combining DFT and deep-learning simulations to reveal dynamic mechanisms.

Findings

Giant piezoelectric response (>320 pC/N) in strained ferroelectric membranes.

Identification of a 'dipole spiral' topological structure with zero-energy rotational mode.

Dynamic dipole rotations at domain walls enhance piezoelectric effects.

Abstract

Freestanding ferroelectric oxide membranes emerge as a promising platform for exploring the interplay between topological polar ordering and dipolar interactions that are continuously tunable by strain. Our investigations combining density functional theory (DFT) and deep-learning-assisted molecular dynamics simulations demonstrate that DFT-predicted strain-driven morphotropic phase boundary involving monoclinic phases manifest as diverse domain structures at room temperatures, featuring continuous distributions of dipole orientations and mobile domain walls. Detailed analysis of dynamic structures reveals that the enhanced piezoelectric response observed in stretched PbTiO$_3$ membranes results from small-angle rotations of dipoles at domain walls, distinct from conventional polarization rotation mechanism and adaptive phase theory inferred from static structures. We identify a ferroelectric topological structure, termed "dipole spiral," which exhibits a giant intrinsic piezoelectric response ($>$320 pC/N). This helical structure, possessing a rotational zero-energy mode, unlocks new possibilities for exploring chiral phonon dynamics and dipolar Dzyaloshinskii-Moriya-like interactions.