Disentangling multipole resonances through a full x-ray polarization analysis

Complete polarization analysis applied to resonant x-ray scattering at the Cr K edge in K2CrO4 shows that incident linearly polarized x rays can be converted into circularly polarized x rays by diffraction at the Cr pre-edge (E=5994 eV). The physical mechanism behind this phenomenon is a subtle interference effect between purely dipole (E1-E1) and purely quadrupole (E2-E2) 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.