Resonant X-ray emission with a standing wave excitation

Kari O Ruotsalainen,Ari-Pekka Honkanen,Simo Huotari,Mikko Hakala,Giulio Monaco,Stephen P Collins,Keijo Hämäläinen,Michael Krisch,Marco Moretti Sala

doi:10.1038/srep22648

Abstract

The Borrmann effect is the anomalous transmission of x-rays in perfect crystals under diffraction conditions. It arises from the interference of the incident and diffracted waves, which creates a standing wave with nodes at strongly absorbing atoms. Dipolar absorption of x-rays is thus diminished, which makes the crystal nearly transparent for certain x-ray wave vectors. Indeed, a relative enhancement of electric quadrupole absorption via the Borrmann effect has been demonstrated recently. Here we show that the Borrmann effect has a significantly larger impact on resonant x-ray emission than is observable in x-ray absorption. Emission from a dipole forbidden intermediate state may even dominate the corresponding x-ray spectra. Our work extends the domain of x-ray standing wave methods to resonant x-ray emission spectroscopy and provides means for novel spectroscopic experiments in d- and f-electron systems.

Highlights

The Borrmann effect is the anomalous transmission of x-rays in perfect crystals under diffraction conditions
It can be stated that the introduction of resonant x-ray spectroscopies turned over the notion that the core hole lifetime is a fundamental limit to the energy resolution obtainable in x-ray absorption spectra
In contrast with the Borrmann spectroscopy introduced by Pettifer et al, measuring the resonant x-ray emission spectrum under the Borrmann condition provides a stark contrast between the electric dipolar and quadrupolar transitions even at room temperature

Summary

Introduction

The Borrmann effect is the anomalous transmission of x-rays in perfect crystals under diffraction conditions. It arises from the interference of the incident and diffracted waves, which creates a standing wave with nodes at strongly absorbing atoms. Our work extends the domain of x-ray standing wave methods to resonant x-ray emission spectroscopy and provides means for novel spectroscopic experiments in d- and f-electron systems. The absorption owing to the electric dipole (E1) term depends on the field amplitude at the atomic sites and the attenuation of the α-branch is diminished while the β-branch, in turn, is absorbed rapidly[16,17]. Pettifer et al demonstrated using the Borrmann effect a very large relative enhancements of electric quadrupole (E2) resonances at the Gd L edges in Gd3Ga5O12, where the normally weak quadrupole-allowed pre-edges www.nature.com/scientificreports/

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