Investigating electronic structure and excitations under extreme conditions gives access to a rich variety of phenomena. High pressure typically induces behavior such as magnetic collapse and the insulator-metal transition in 3d transition metals compounds, valence fluctuations or Kondo-like characteristics in $f$-electron systems, and coordination and bonding changes in molecular solids and glasses. This article reviews research concerning electronic excitations in materials under extreme conditions using inelastic x-ray scattering (IXS). IXS is a spectroscopic probe of choice for this study because of its chemical and orbital selectivity and the richness of information it provides. Being an all-photon technique, IXS has a penetration depth compatible with high pressure requirements. Electronic transitions under pressure in 3d transition metals compounds and $f$-electron systems, most of them strongly correlated, are reviewed. Implications for geophysics are mentioned. Since the incident X-ray energy can easily be tuned to absorption edges, resonant IXS, often employed, is discussed at length. Finally studies involving local structure changes and electronic transitions under pressure in materials containing light elements are briefly reviewed.
Resonant inelastic x-ray scattering of magnetic excitations under pressure
共振非弹性X射线散射（RIXS）是研究物质中元素（包括磁性）激发的一种非常有价值的工具。该技术的最新发展主要是提高能量分辨率和对散射辐射进行偏振分析，这对RIXS的解释和适用性产生了很大影响。相反，这篇文章的重点是样品环境，并提出了一个设置为低能量激发的高压低温RIXS测量。这些实验的可行性被证明通过探测双层铱酸盐Sr $_3$ Ir $_2$ O $_7$在压力高达12 GPa的磁激发。
Comprehensive Research Organization for Science and Society (CROSS)（综合科学研究组织）；Tohoku University（东北大学）；Japan Atomic Energy Agency (JAEA)（日本原子能研究开发机构）；Ibaraki University（茨城大学）；Tokyo City University（东京都立大学）；The University of Tokyo（东京大学）
Sudden reversal in the pressure dependence of Tc in the iron-based superconductor CsFe2As2: A possible link between inelastic scattering and pairing symmetry
Magnetic spectral response and lattice properties in mixed-valence Sm1-x Yx S solid solutions studied with x-ray diffraction, x-ray absorption spectroscopy, and inelastic neutron scattering
