Figure 2. Kinetics pathways of polarization reversal processes.

(a) Evolution of the total energy (y axis) of 1 quintuple layer (QL) In₂Se₃ in the FE-ZB′ phase transforming from the state with the electric polarization pointing downward (left) to the state with the electric polarization pointing upward (right) via a direct shifting process: the Se atoms in the central layer laterally shift from the B to C sites. The green arrows attached to atoms indicate the directions of atomic motion during the polarization reversal processes, which are in the plane perpendicular to the In₂Se₃ layer and passing through the green dashed line as shown in the top view. (b) Energy profile of the most effective kinetic pathway to reverse the orientation of the electric polarization of one QL In₂Se₃ in the FE-ZB′ phase involving a three-step concerted mechanism, as detailed in the main text. The activation barrier of the concerted motion is lower than the direct shifting process by an order of magnitude (note that the height of the barrier shown in a is scaled down by a factor of 10).