Phonon dispersion of quantum paraelectric SrTiO3 in electric fields

TL;DR

This study investigates how electric fields influence the lattice dynamics of quantum paraelectric SrTiO3 using neutron scattering, revealing weak coupling of octahedral rotations and hints of non-linear phonon interactions.

Contribution

It provides detailed experimental insights into the effects of electric fields on phonon dispersion and lattice dynamics in SrTiO3, complementing recent theoretical predictions.

Findings

Small changes in superlattice reflections with electric field

Hints of non-linear coupling between phonons and acoustic modes

Quantification of electric field effects on phonon dispersion

Abstract

Here we report on an elastic and inelastic neutron scattering study addressing the effect of electric fields on quantum paraelectric SrTiO3. Our elastic scattering results find small changes as a function of field in a superlattice reflection that sample the octahedral rotations, which is indicative of only weak coupling of octahedral rotation and electric polarization. By collecting not only the change in gap, but also of the dispersion, we can better quantify the changes in the lattice dynamics. The findings are put in context to recent field DFT calculations predicting the E-field effect on the atomic motions of the lowest lying transverse optical (soft) mode. We find hints of non-linear coupling to the acoustic mode and to the phonon with polarization perpendicular to the E-field, which shows the non-linearity in the chemical potential that is also relevant when strongly driving SrTiO3 with E-field (THz) pulses.