Squishing Skyrmions: Symmetry-Guided Dynamic Transformation of Polar Topologies Under Compression

Mechanical controllability of recently discovered topological
defects
(e.g., skyrmions) in ferroelectric materials is of
interest for the development of ultralow-power mechano-electronics
that are protected against thermal noise. However, fundamental understanding
is hindered by the “multiscale quantum challenge” to
describe topological switching encompassing large spatiotemporal scales
with quantum mechanical accuracy. Here, we overcome this challenge
by developing a machine-learning-based multiscale simulation frameworka
hybrid neural network quantum molecular dynamics (NNQMD) and molecular
mechanics (MM) method. For nanostructures composed of SrTiO3 and PbTiO3, we find how the symmetry of mechanical loading
essentially controls polar topological switching. We find under symmetry-breaking uniaxial compression a squishing-to-annihilation
pathway versus formation of a topological composite named skyrmionium
under symmetry-preserving isotropic compression.
The distinct pathways are explained in terms of the underlying materials’
elasticity and symmetry, as well as the Landau–Lifshitz–Kittel
scaling law. Such rational control of ferroelectric topologies will
likely facilitate exploration of the rich ferroelectric “topotronics”
design space.