Hexagonal close-packed polar-skyrmion lattice in ultrathin ferroelectric PbTiO3 films

TL;DR

This study uses phase-field simulations to explore the formation and stability of a hexagonal close-packed polar-skyrmion lattice in ultrathin ferroelectric PbTiO3 films, revealing how external electric fields and film thickness influence the phase behavior.

Contribution

It demonstrates the stabilization of a hexagonal skyrmion lattice in ultrathin ferroelectric films and maps the phase diagram considering electric field, temperature, and thickness effects.

Findings

Hexagonal skyrmion lattice can be stabilized with an external electric field.

Lattice constants increase with film thickness, following Kittel law.

Phase diagram shows conditions for skyrmion lattice stability.

Abstract

Polar skyrmions are topologically stable, swirling polarization textures with particle-like characteristics, which hold promise for next-generation, nanoscale logic and memory. While understanding of how to create ordered polar skyrmion lattice structures and how such structure respond to applied electric fields, temperature, and film thickness remains elusive. Here, using phase-field simulations, the evolution of polar topology and the emergence of a phase transition to a hexagonal close-packed skyrmion lattice is explored through the construction of a temperature-electric field phase diagram for ultrathin ferroelectric PbTiO3 films. The hexagonal-lattice skyrmion crystal can be stabilized under application of an external, out-of-plane electric field which carefully adjusts the delicate interplay of elastic, electrostatic, and gradient energies. In addition, the lattice constants of the polar skyrmion crystals are found to increase with film thickness, consistent with expectation from Kittel law. Our studies pave the way for the development of novel ordered condensed matter phases assembled from topological polar textures and related emergent properties in nanoscale ferroelectrics.