We present the observation of peculiar nonmonotonic photon energy dependencies of the count rates and of the rocking curves of parametric down-conversion of x rays into ultraviolet far from any atomic resonances. The observations cannot be explained by models that consider only atomic or bond charge responses and suggest that collective phenomena contribute to the effect. We propose an interpretation that includes nonlinear interactions with plasmons, which can explain the existence of peaks in this energy range. Our Letter implies that nonlinear interactions between x rays and either ultraviolet or visible radiation can be utilized as a powerful atomic-scale probe for collective effects in solids.
|Journal||Physical Review Letters|
|State||Published - 16 Jan 2019|
Bibliographical noteFunding Information:
This work was supported by the Israel Science Foundation (ISF), Grant No. 201/17. We acknowledge SOLEIL synchrotron for the provision of synchrotron facilities (Proposal No. 20160046).
© 2019 American Physical Society.