Theory of resonant X-ray emission spectra in strongly correlated electron systems

Theoretical calculations of resonant X-ray emission spectrum (RXES) in rare earth systems and transition metal compounds are presented and compared with recent experimental data. RXES is formulated as a coherent second-order optical process, in contrast to that X-ray absorption spectrum (XAS) and X-ray photoemission spectrum (XPS) are the first-order optical process, and is calculated with atomic model or impurity Anderson model. From the analysis of RXES we can obtain important information on electronic excitations in rare earth systems and transition metal compounds, such as the multiplet excitation, the charge transfer excitation and the crystal field level excitation. The cluster size dependence of XAS, XPS and RXES is also studied theoretically with a one-dimensional d-p model, which describes qualitatively the effect of translational symmetry for nominally d degrees (or f degrees) compounds such as TiO2 (CeO2). (C) 2000 Elsevier Science B.V. All rights reserved.