paper

Proposal for midinfrared light--induced ferroelectricity in oxide paraelectrics

arXiv:1612.04788 · doi:10.1103/PhysRevB.95.134113

Abstract

I show that a nonequilibrium paraelectric to ferroelectric transition can be induced using midinfrared pulses. This relies on a quartic $lQ_{\textrm{l$_z$}}^2Q_{\textrm{h$_x$}}^2$ coupling between the lowest ($Q_{\textrm{l$_z$}}$) and highest ($Q_{\textrm{h$_x$}}$) frequency infrared-active phonon modes of a paraelectric material. Density functional calculations show that the coupling constant is negative, which causes a softening of the $Q_{\textrm{l$_z$}}$ mode when the $Q_{\textrm{h$_x$}}$ mode is externally pumped. A rectification along the $Q_{\textrm{l$_z$}}$ 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 $Q_{\textrm{h$_x$}}$ mode shows that ferroelectricity can be induced in the representative case of strained KTaO by a midinfrared pulse with a peak electric field of 17 MV cm 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.

10 pages, 6 figures

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