Complete polarization analysis applied to resonant x-ray scattering at the Cr $K$ edge in ${\mathrm{K}}_2\mathrm{Cr}{\mathrm{O}}_4$ shows that incident linearly polarized x rays can be converted into circularly polarized x rays by diffraction at the Cr pre-edge $(E=5994\mathrm{eV})$. The physical mechanism behind this phenomenon is a subtle interference effect between purely dipole $\left(E1\text{−}E1\right)$ and purely quadrupole $\left(E2\text{−}E2\right)$ transitions, leading to a phase shift between the respective scattering amplitudes. This effect may be exploited to disentangle two close-lying resonances that appear as a single peak in a conventional energy scan, in this way allowing one to single out and identify the different multipole order parameters involved.

• Received 2 July 2007

DOI:https://doi.org/10.1103/PhysRevB.76.195118