Proposal for ultrafast switching of ferroelectrics using midinfrared pulses

I propose a method for ultrafast switching of ferroelectric polarization using midinfrared pulses. This involves selectively exciting the highest frequency A₁ phonon mode of a ferroelectric material with an intense midinfrared pulse. Large amplitude oscillations of this mode provides a unidirectional force to the lattice such that it displaces along the lowest frequency A₁ phonon mode coordinate because of a nonlinear coupling of the type gQPQIR² between the two modes. First-principles calculations show that this coupling is large in perovskite transition-metal oxide ferroelectrics, and the sign of the coupling is such that the lattice displaces in the switching direction. Furthermore, I find that the lowest frequency A₁ mode has a large QP³ order anharmonicity, which causes a discontinuous switch of electric polarization as the pump amplitude is continuously increased.