Resonant X-ray Emission Spectroscopy With a Standing Wave Excitation

TL;DR

This paper demonstrates that the Borrmann effect significantly enhances resonant x-ray emission, enabling new spectroscopic techniques for studying complex electronic systems.

Contribution

It extends x-ray standing wave methods to resonant x-ray emission spectroscopy, revealing larger effects than previously observed in absorption.

Findings

Borrmann effect greatly enhances resonant x-ray emission.

Dipole forbidden states can dominate emission spectra.

New spectroscopic experiments in d- and f-electron systems are enabled.

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.