Disentangling multipole resonances through a full x-ray polarization analysis

TL;DR

This paper demonstrates how full polarization analysis in resonant x-ray scattering can reveal interference effects between dipole and quadrupole transitions, enabling the disentanglement of overlapping multipole resonances.

Contribution

It introduces a method to distinguish and analyze multipole resonances using polarization analysis at the Cr K-edge, revealing interference effects.

Findings

Incident linearly polarized x-rays can be converted into circular polarization.

Interference between dipole and quadrupole transitions causes phase shifts.

The method allows identification of different multipole order parameters.

Abstract

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 to single out and identify the different multipole order parameters involved.