Introduction to High-Resolution Inelastic X-Ray Scattering

This paper reviews non-resonant, meV-resolution inelastic x-ray scattering (IXS), as applied to the measurement of atomic dynamics of crystalline materials. It is designed to be an introductory, though in-depth, look at the field for those who be may interested in performing IXS experiments, or in understanding the operation of IXS spectrometers, or those desiring a practical introduction to harmonic phonons in crystals at finite momentum transfers. The treatment of most topics begins from ground-level, with a strong emphasis on practical issues, as they have occurred to the author in two decades spent introducing meV-resolved IXS in Japan, including designing and helping to build two IXS beamlines, spectrometers and associated instrumentation, performing experiments, and helping and teaching other scientists. After an introduction that compares IXS to other methods of investigating atomic dynamics, some of the basic principles of scattering theory are described with the aim of introducing useful and relevant concepts for the experimentalist. That section includes a fairly detailed discussion of harmonic phonons. The theory section is followed by a brief discussion of calculations and then a longer section on spectrometer design, concepts, and implementation, including a brief introduction to dynamical diffraction and a survey of presently available instruments. Finally, there is discussion of the types of experiments that have been carried out, with a focused discussion on measurements of superconductors, and brief discussion (but with many references) of other types of crystalline samples.