%0 Journal Article
%A Ye, Lyuzhou
%A Rouxel, Jérémy R.
%A Cho, Daeheum
%A Mukamel, Shaul
%T Imaging electron-density fluctuations by multidimensional X-ray photon-coincidence diffraction
%D 2019
%R 10.1073/pnas.1816730116
%J Proceedings of the National Academy of Sciences
%P 395-400
%V 116
%N 2
%X X-ray diffraction is routinely used to monitor the ground-state electronic charge density of molecules or the motion of nuclei. In this work, we propose a spectroscopic measurement based on multidimensional photon-coincidence X-ray diffraction, which probes the correlation functions of the charge densities in momentum space. The inverse Fourier-transformed signal in real space, which is a combination of correlation functions of transition charge densities, allows us to identify the various scattering pathways that dominate the signal in momentum space and provides most valuable information on spontaneous electronic fluctuations and correlations.The ultrafast spontaneous electron-density fluctuation dynamics in molecules is studied theoretically by off-resonant multiple X-ray diffraction events. The time- and wavevector-resolved photon-coincidence signals give an image of electron-density fluctuations expressed through the four-point correlation function of the charge density in momentum space. A Fourier transform of the signal provides a real-space image of the multipoint charge-density correlation functions, which reveal snapshots of the evolving electron density in between the diffraction events. The proposed technique is illustrated by ab initio simulations of the momentum- and real-space inelastic scattering signals from a linear cyanotetracetylene molecule.
%U https://www.pnas.org/content/pnas/116/2/395.full.pdf