Ultrafast reversal of the ferroelectric polarization

TL;DR

This paper demonstrates ultrafast optical switching of ferroelectric polarization in LiNbO3 using femtosecond mid-infrared pulses to excite phonon modes, achieving reversal on femtosecond timescales, much faster than electric field methods.

Contribution

It introduces a novel method of reversing ferroelectric polarization via indirect resonant excitation of phonons, enabling ultrafast switching in LiNbO3.

Findings

Polarization reversal achieved in femtoseconds

Reversal can be induced in both directions

Coupling to high-frequency phonons enables control

Abstract

The ability to manipulate ferroelectrics at ultrafast speeds has long been an elusive target for materials research. Coherently exciting the ferroelectric mode with ultrashort optical pulses holds the promise to switch the ferroelectric polarization on femtosecond timescale, two orders of magnitude faster compared to what is possible today with pulsed electric fields. Here, we report on the demonstration of ultrafast optical reversal of the ferroelectric polarization in LiNbO3. Rather than driving the ferroelectric mode directly, we couple to it indirectly by resonant excitation of an auxiliary high-frequency phonon mode with femtosecond mid-infrared pulses. Due to strong anharmonic coupling between these modes, the atoms are directionally displaced along the ferroelectric mode and the polarization is transiently reversed, as revealed by time-resolved, phase-sensitive second-harmonic generation. This reversal can be induced in both directions, a key pre-requisite for practical applications.