Midinfrared-light-induced ferroelectricity in oxide paraelectrics via nonlinear phononics

I show that a nonequilibrium paraelectric to ferroelectric transition can be transiently induced using midinfrared pulses. This relies on a quartic lQlz2Qhx2 coupling between the lowest (Qlz) and highest (Qhx) frequency infrared-active phonon modes of a paraelectric material. Density functional calculations show that the coupling constant l is negative, which causes a softening of the Qlz mode when the Qhx mode is externally pumped. A rectification along the Qlz coordinate that stabilizes the nonequilibrium ferroelectric state occurs only above a critical threshold for the electric field of the pump pulse, demonstrating that this is a nonperturbative phenomenon. A first-principles calculation of the coupling between light and the Qhx mode shows that ferroelectricity can be induced in the representative case of strained KTaO3 by a midinfrared pulse with a peak electric field of 17MVcm-1 and duration of 2 ps. Furthermore, other odd-order nonlinear couplings make it possible to arbitrarily switch off the light-induced ferroelectric state, making this technique feasible for all-optic devices.