Anisotropic resonant X-ray scattering: Beauty of forbidden reflections

J Kokubun,V E Dmitrienko

doi:10.1140/epjst/e2012-01605-4

J Kokubun, V E Dmitrienko

Open Access

https://doi.org/10.1140/epjst/e2012-01605-4

Copy DOI

Abstract

Experimental results and their theoretical explanation are reviewed for fundamentals of anisotropic resonant X-ray scattering. Resonant scattering depends on X-ray polarization, i.e. the scattering reflects anisotropic environment of atoms in crystal. The polarization anisotropy in atomic scattering can excite the forbidden Bragg reflections. Studying this type of forbidden reflections we can distinguish electronic orbitals of specific symmetry. This method is very useful for studying local electronic states in crystal. We reveal detailed property of the anisotropic scattering, effect of quadrupole transition, thermal motion, magnetic scattering and so on. Especially successful examples are given in detail: observation of phase of the scattering factor, the hybridization of states with different parity, local chirality of atom in centrosymmetric crystals, thermal-motion-induced resonant reflections, etc.

Highlights

Resonant X-ray scattering essentially depends on X-ray polarization as well as energy
We show additional and complicated physical phenomena concerning resonant scattering, in particular, we consider the influence of the magnetic scattering, thermal motion and so on
We have presented only a small part of works dealing with forbidden reflections in resonant regions near X-ray absorption edges

Summary

Introduction

Resonant X-ray scattering essentially depends on X-ray polarization as well as energy. In 1982, Templeton and Templeton [3] observed nonforbidden reflections intensities dependent on X-ray polarization and supposed that a special type of forbidden reflections can be excited owing to the polarization anisotropy This polarization effect is caused by electric anisotropy of resonant atoms near the absorption edge. From these results it was pointed [4, 5] out that the atomic scattering factor should be treated as tensor and traditional extinction rules for Bragg reflections were violated. The forbidden reflection was strongly dependent on temperature and this result revealed that the large part of the intensity was caused by thermal-motion-induced (TMI) resonant scattering [23]. It is demonstrated that the quadrupole scattering effect is typical of many crystals

Basic theory

Experimental

Results and discussion

Conclusion