Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics

TL;DR

This paper explores high-field nonlinear phononics in solids, using intense mid-infrared pulses to drive multiple phonon harmonics in LiNbO3, enabling reconstruction of the interatomic potential and benchmarking theoretical models.

Contribution

It demonstrates an order-of-magnitude increase in field strength to probe higher-order lattice nonlinearities and reconstruct the interatomic potential experimentally.

Findings

Successfully driven up to five phonon harmonics in LiNbO3

Reconstructed the interatomic potential from phase-sensitive measurements

Benchmarked ab-initio calculations against experimental data

Abstract

Femtosecond optical pulses at mid-infrared frequencies have opened up the nonlinear control of lattice vibrations in solids. So far, all applications have relied on second order phonon nonlinearities, which are dominant at field strengths near 1 MVcm-1. In this regime, nonlinear phononics can transiently change the average lattice structure, and with it the functionality of a material. Here, we achieve an order-of-magnitude increase in field strength, and explore higher-order lattice nonlinearities. We drive up to five phonon harmonics of the A1 mode in LiNbO3. Phase-sensitive measurements of atomic trajectories in this regime are used to experimentally reconstruct the interatomic potential and to benchmark ab-initio calculations for this material. Tomography of the Free Energy surface by high-order nonlinear phononics will impact many aspects of materials research, including the study of classical and quantum phase transitions.