Unconventional ferroelectric domain switching dynamics in CuInP2S6 from first principles

The switching dynamics of ferroelectric materials is a crucial intrinsic property which directly affects the operation and performance of ferroelectric devices. In conventional ferroelectric materials, the typical ferroelectric switching mechanism is governed by a universal process of domain-wall motion. However, recent experiments indicate that van der Waals ferroelectric $\mathrm{CuIn}{\mathrm{P}}₂{\mathrm{S}}₆$ possesses anomalous polarization switching dynamics under an electric field. It is important to understand the switching dynamics, but it remains theoretically unexplored in $\mathrm{CuIn}{\mathrm{P}}₂{\mathrm{S}}₆$ due to the lack of description of its order-disorder phase transition characteristics by density functional theory. Here we employ a machine-learning potential trained from the first-principles density functional theory dataset to conduct large-scale atomistic simulations of temperature-driven order-disorder ferroelectric phase transition in $\mathrm{CuIn}{\mathrm{P}}₂{\mathrm{S}}₆$. Most importantly, it is found that the electric-field-driven polarization switching in $\mathrm{CuIn}{\mathrm{P}}₂{\mathrm{S}}₆$ is mediated by a single Cu dipole flip rather than a conventional domain-wall-motion mechanism. This intrinsic unconventional switching behavior can be attributed to the competition between the energy barrier of domain-wall motion and single-dipole flip.