Resonant X-ray Scattering

In this chapter we provide a brief introduction to resonant x-ray scattering (RXS) and x-ray absorption spectroscopy (XAS) as tools to probe correlated electronic states in transition metal oxides. Unlike conventional non-resonant x-ray diffraction, experimental techniques which make use of electronic resonances are inherently spectroscopic in nature. As such, resonant x-ray scattering combines the strength of a diffraction experiment (high spatial resolution) with spectroscopic sensitivity. This favourable combination allows one to probe spatial modulations in an element and electronic-state specific manner. Furthermore, the enormous enhancement of the scattering cross section which is afforded on resonance permits the observation of low-energy electronic and magnetic correlations which are otherwise too weak to detect. This high level of sensitivity can also be exploited to study small sample volumes, including state-of-the-art nanostructures composed of mere atomic layers.