Ferroelectric phase transition driven by anharmonic lattice mode coupling in two-dimensional monolayer In2Se3

In this paper, to better understand the physical origin of spontaneous out-of-plane (OOP) polarization in the wildly investigated two-dimensional (2D) material monolayer (ML) ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$, we studied its lattice dynamics behaviors via performing a series of first-principles calculations. Cooperating with a fitted phenomenological model, it is clearly shown that, although the depolarization field is nonzero, spontaneous OOP polarization will survive through the anharmonic coupling with other lattices modes. Additionally, our results indicated that the conventional proper ferroelectric (FE) transition of in-plane (IP) polarization plays a role in the primary driving force for the transition in lattice. Tuning the stability of the IP polar modes can be considered an effective pathway of controlling the FE behavior in ML ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ and related III-VI group 2D materials.