Phonon Spectroscopy with Sub-meV Resolution by Femtosecond X-ray Diffuse Scattering

TL;DR

This paper demonstrates high-resolution femtosecond x-ray diffuse scattering to reconstruct germanium's phonon dispersion with sub-meV energy resolution, enabling rapid, comprehensive phonon mapping without scanning.

Contribution

It introduces a method for high-resolution, rapid phonon dispersion measurement using femtosecond x-ray diffuse scattering, avoiding extensive scanning.

Findings

Achieved 0.3 meV energy resolution for phonon dispersion.

Reconstructed phonon dispersion in less than three hours.

Method complements traditional inelastic scattering techniques.

Abstract

We present a reconstruction of the transverse acoustic phonon dispersion of germanium from femtosecond time-resolved x-ray diffuse scattering measurements at the Linac Coherent Light Source. We demonstrate an energy resolution of 0.3 meV with momentum resolution of 0.01 nm^-1 using 10 keV x-rays with a bandwidth of ~ 1 eV. This high resolution was achieved simultaneously for a large section of reciprocal space including regions closely following three of the principle symmetry directions. The phonon dispersion was reconstructed with less than three hours of measurement time, during which neither the x-ray energy, the sample orientation, nor the detector position were scanned. These results demonstrate how time-domain measurements can complement conventional frequency domain inelastic scattering techniques.