Figure 4.

Dynamics of the normal-modes under the x-polarized pulse (a,b) without and (c) with damping. (a) Amplification of the Q_LSy mode through the anharmonic force by the pulse at 0 K. (b) At 300 K, the Q_LSy has sufficient kinetic energy to overcome the effective energy barrier (〈Φ〉 = 11.5 meV at |Q_IRx| = 5.35 Å$\sqrt{\mu }$) after the pumping, and oscillates back and forth between AB (Q_LSy = 0 Å$\sqrt{\mu }$) and AC (Q_LSy = 16.29 Å$\sqrt{\mu }$) stackings. (c) In the presence of damping, the Q_LSy mode at 0 K overcomes the energy barrier after eight sequential pulses. The AB stacking changes to the AC stacking and does not return due to the dissipation of kinetic energy. (d) Schematics of ferroelectric switching through the Q_IRx-Q_LSy coupling. The orange arrows indicates the directions of interlayer shear induced by the x-polarized pulse, which are opposite in the AB and AC stackings.