Resonant X-Ray Fluorescence Spectroscopy of Correlated Systems: A Probe of Charge-Transfer Excitations

X-ray fluorescence spectroscopy with monochromatic photon excitation is presented as a tool for studies of charge-transfer excitations in correlated systems, using Ce${\mathrm{O}}_2$ and U${\mathrm{O}}_3$ as examples. Ce $4f\to 3d$ and U $5f\to 3d$ x-ray fluorescence, with excitation near the $3d$ thresholds, probes states as eigenvalues for the ground state Hamiltonian from the Anderson impurity model. Sweeping the excitation energy across $3d$ absorption edges enhances contributions of different electronic configurations to fluorescence so that observed resonances indicate the charge-transfer origin of the absorption satellites.