Inelastic X-ray Scattering Studies of Electronic Excitations

Abstract

Inelastic x-ray scattering (IXS) has developed into one of the most powerful momentum-resolved spectroscopies. Especially in the last decade, it has achieved significant progress utilizing brilliant x-rays from third-generation synchrotron radiation facilities. Simultaneously, theoretical efforts have been made to predict or interpret the experimental spectra. One of the scientific fields studied intensively by IXS is strongly correlated electron systems, where the interplay of charge, spin, and orbital degrees of freedom determines their physical properties. IXS can provide a new insight into the electron dynamics of the systems through the observation of charge, spin, and orbital excitations. Focusing on the momentum-resolved electronic excitations in strongly correlated electron systems, we review IXS studies and the present capabilities of IXS for the study of the dynamics of materials. With nonresonant inelastic x-ray scattering (NIXS), one can directly obtain dynamical charge correlation and we discuss its complementary aspects with inelastic neutron scattering. NIXS also has a unique capability of measuring higher multipole transitions, which are usually forbidden in conventional optical absorption. Resonant inelastic x-ray scattering (RIXS) is now established as a valuable tool for measuring charge, spin, and orbital excitations in a momentum-resolved manner. We describe RIXS works on cuprates in detail and show what kind of electronic excitations have been observed. We also discuss RIXS studies on other transition-metal compounds. Finally, we conclude with an outlook on IXS using next-generation x-ray sources.

Insights into the high temperature superconducting cuprates from resonant inelastic X-ray scattering

“…Outside the scope of this review, RIXS studies have been important in determining the electronic properties of the cuprates, a field that has been reviewed in [136,5,22], and L-edge RIXS studies of non-cuprate materials such as iridates and pnictides have also been highly instructive. It has been a time of rapid progress for soft x-ray RIXS, fueled by improvements in energy resolution, and this pace of change looks set to continue in the coming years with the advert of multiple high-resolution RIXS beamlines.…”

Analysis of resonant inelastic x-ray scattering fromSr2IrO4in an itinerant-electron approach

“…Strong synchrotron sources have been rapidly developing, and resonant inelastic x-ray scattering (RIXS) has become a powerful tool to probe elementary excitations in solids [1,2]. Both the K-and L-edge resonances are utilized in transition-metal compounds.…”

Exciton energy-momentum map of hexagonal boron nitride

“…This assessment is now possible thanks to the spectacular progress of inelastic x-ray scattering (IXS) experiments, both in the resonant (RIXS) and non-resonant (NRIXS) conditions. They allow one to probe electronic excitations at finite momenta (q) [9] with a resolving power that has improved by orders of magnitude * Corresponding author: giorgia.fugallo@polytechnique.edu in the last two decades [10][11][12][13]. The challenge for theory is hence the first-principles description of the full electron dynamics [10], which is well beyond the sole simulation of optical absorption spectra.…”