Ultrafast x-ray diffraction probe of terahertz field-driven soft mode dynamics

TL;DR

This study employs ultrafast x-ray diffraction to investigate how strong terahertz fields influence the soft optical phonon modes in SrTiO3, revealing transient lattice dynamics and temperature-dependent softening of specific modes.

Contribution

It demonstrates the use of ultrafast x-ray diffraction to directly observe terahertz-driven soft mode dynamics in a complex oxide material.

Findings

Transient diffraction intensity changes with delayed onset

Identification of two frequency components in lattice response

Softening of the lower frequency mode at lower temperatures

Abstract

We use ultrafast x-ray pulses to characterize the lattice response of SrTiO3 when driven by strong terahertz (THz) fields. We observe transient changes in the diffraction intensity with a delayed onset with respect to the driving field. Fourier analysis reveals two frequency components corresponding to the two lowest energy zone-center optical modes in SrTiO3. The lower frequency mode exhibits clear softening as the temperature is decreased while the higher frequency mode shows slight temperature dependence.