Nonlocal nonlinear phononics

M Henstridge,M Fechner,A Cavalleri,M Först,E Rowe

doi:10.1038/s41567-022-01512-3

Abstract

Nonlinear phononics relies on the resonant optical excitation of infrared-active lattice vibrations to induce targeted structural deformations in solids. This form of dynamical crystal structure design has been applied to control the functional properties of many complex solids, including magnetic materials, superconductors and ferroelectrics. However, phononics has so far been restricted to protocols in which structural deformations occur within the optically excited volume, sometimes resulting in unwanted heating. Here, we extend nonlinear phononics to propagating polaritons, spatially separating the functional response from the optical drive. We use mid-infrared optical pulses to resonantly drive a phonon at the surface of ferroelectric LiNbO3. Time-resolved stimulated Raman scattering reveals that the ferroelectric polarization is reduced over the entire 50 µm depth of the sample, far beyond the micrometre depth of the evanescent phonon field. We attribute this effect to the anharmonic coupling between the driven mode and a polariton that propagates into the material. For high excitation amplitudes, we reach a regime in which the ferroelectric polarization is reversed, as revealed by a sign change in the Raman tensor coefficients of all the polar modes.

Highlights

Nonlinear phononics relies on the resonant optical excitation of infrared-active lattice vibrations to induce targeted structural deformations in solids
If the material breaks inversion symmetry, the optically excited mode can exert a displacive force onto symmetry-odd modes, which can propagate as polaritons. This type of phonon–polariton coupling opens up a broad class of phenomena that we term nonlocal nonlinear phononics
Polariton excitation through phononics builds on extensive previous work in which polaritons were excited using impulsive stimulated Raman scattering from propagating near-infrared pulses[11,12]

Summary

Introduction

Nonlinear phononics relies on the resonant optical excitation of infrared-active lattice vibrations to induce targeted structural deformations in solids. In the experiments reported here, LiNbO3 single crystals were illuminated with mid-infrared pulses of 20 THz central frequency and 150 fs duration, with fluences that extended up to nearly 200 mJ cm−2, that is, peak electric fields up to 30 MV cm−1.

Results

Conclusion