Resonant Elastic X-ray Scattering

Resonant Elastic X-ray Scattering (REXS, or RXS) is a synchrotron x-ray technique that combines diffraction and spectroscopy allowing the simultaneous measurement of atomic and electronic ordering. RXS can be used to increase the signal from magnetic ordering and can be used to seperate magnetic, orbital and charge contributions to a scattered signal.

By tuning the incident x-ray energy to an absorption edge of an element in your sample, core-electrons are promoted to empty states in the valence band, in the same was as a spectroscopy measurement. These excited electrons then return to their core-holes (via several routes), emitting photons as they do. In the case of resonant diffraction, these emitted photons are coherent and interfere constructivly, creating an increase in diffracted signal. In cases where the electronic states break the symmetry of the crystalline lattice, this can create diffracted signals at extinctions - for instance antiferromagnetic signals appear half-way between diffraction peaks of the underlying lattice. 

Benefits of Synchrotron Techniques

The ability to tune the energy of the incident beam allows us to measure the absorption edges of many 3d, 4d, 5d tranisiton metals to asses their electronic states and electronic ordering phenomena, from magnetism to charge density waves. Hard x-ray beamlines such as I16 can access absorption edges between 2.5 keV and 15 keV, which includes the K edges of 3d metals, the L edges of 4d and 5d metals and the M edges of the Actinides. Soft x-ray beamlines such as I10 can access absorption edges in the soft energy range.

Applications

This technique is used to enhance extremely weak scattering effects from magnetic ordering, allowing us to determine the symmetry and orientation of magnetic moments in many crystalline materials. The technique is also useful to seperate electronic phenomena in strongly correlated materials and can even be used to separate different elements sitting at the same crystallographic site.