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Register a new userProposal for ultrafast switching of ferroelectrics using mid-infrared pulses
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Alaska Subedi
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I propose a method for ultrafast switching of ferroelectric polarization using mid-infrared pulses. This involves selectively exciting the highest frequency $A_1$ phonon mode of a ferroelectric material with an intense mid-infrared pulse. Large amplitude oscillations of this mode provides a unidirectional force to the lattice such that it displaces along the lowest frequency $A_1$ phonon mode coordinate because of a nonlinear coupling of the type $g Q_{textrm{P}} Q_{textrm{IR}}^2$ between the two modes. First principles calculations show that this coupling is large in 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 $A_1$ mode has a large $Q_{textrm{P}}^3$ order anharmonicity, which causes a discontinuous switch of electric polarization as the pump amplitude is continuously increased.
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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 $l$ 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$_3$ by a midinfrared pulse with a peak electric field of 17 MV cm$^{-1}$ 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.
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