Fourier-transform inelastic X-ray scattering from time- and momentum-dependent phonon–phonon correlations

Authors

M. Trigo, SLAC National Accelerator LaboratoryFollow
Matthias Fuchs, University of Nebraska-LincolnFollow
J. Chen, SLAC National Accelerator Laboratory
M. P. Jiang, SLAC National Accelerator Laboratory
M. Cammarata, SLAC National Accelerator Laboratory
S. Fahey, University College, Cork, Ireland
D. M. Fritz, SLAC National Accelerator Laboratory
Kelly Gafffney, SLAC National Accelerator LaboratoryFollow
S. Ghimire, SLAC National Accelerator Laboratory
A. Higginbotham, University of Oxford
S. L. Johnson, ETH Zurich
M. E. Kozina, SLAC National Accelerator Laboratory
J. Larsson, Lund University
H. Lemke, SLAC National Accelerator Laboratory
A. M. Lindenberg, SLAC National Accelerator Laboratory
G. Ndabashimiye, SLAC National Accelerator Laboratory
F. Quirin, University of Duisburg-Essen
K. Sokolowski-Tinten, University of Duisburg-Essen
C. Uher, University of Michigan - Ann Arbor
G. Wang, University of Michigan - Ann Arbor
J. S. Wark, University of Oxford
D. Zhu, SLAC National Accelerator Laboratory
D. A. Reis, SLAC National Accelerator LaboratoryFollow

Date of this Version

12-2013

Document Type

Article

Citation

NATURE PHYSICS, VOL 9, (DECEMBER 2013), pp. 790-794;
DOI: 10.1038/NPHYS2788

Abstract

The macroscopic characteristics of a material are determined by its elementary excitations, which dictate the response of the system to external stimuli. The spectrum of excitations is related to fluctuations in the density–density correlations and is typically measured through frequency-domain neutron1 or X-ray scattering. Time-domain measurements of these correlations could yield a more direct way to investigate the excitations of solids and their couplings both near to and far from equilibrium. Here we show that we can access large portions of the phonon dispersion of germanium by measuring the diffuse scattering from femtosecond X-ray free-electron laser pulses.A femtosecond optical laser pulse slightly quenches the vibrational frequencies, producing pairs of high-wavevector phonons with opposite momenta. These phonons manifest themselves as time-dependent coherences in the displacement correlations probed by the X-ray scattering. As the coherences are preferentially created in regions of strong electron–phonon coupling, the time-resolved approach is a natural spectroscopic tool for probing low-energy collective excitations in solids, and their microscopic interactions.

Supplementary information and 2 supplementary movies are attached below.