Coherent diffraction imaging at space-group forbidden reflections
Résumé
On one hand, coherent diffraction imaging (CDI) in Bragg geometry has emerged as a unique 3D microscopy of nanocrystals thanks
to 3rd generation synchrotron sources. Away from absorption edges and at space-group allowed reflections, it provides not only the
electronic density, but also, encoded in the phase, the atomic displacement field with respect to the mean lattice, which in turn reveals
crystal strain, defects and domains [1–3]. On the other hand, some crystal structures have crystallographic reflections which are
forbidden by the space-group symmetry but can nevertheless be observed at a suitable X-ray absorption edge, due to the anisotropy of
the tensor of scattering (ATS) [4]. They are several orders of magnitude weaker than allowed reflections, but the absence of Thomson
scattering allows the observation of various electronic phenomena related to electronic orders (magnetic, charge, orbital), static and
dynamic atomic displacements.
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