Random-phase approximation of core-electron energy-loss spectra in solids

The interference between bound-bound transition and bound-free transition in an electron-impact excitation of a core-electron in systems with narrow bands is discussed within the context of diagrammatic perturbation of ladder and ring diagrams in the spirit of random-phase approximation (RPA). [1, 2] The resulting excitation spectrum has been formulated by introducing Fano line shape parameters for the associated autoionization and characteristic decay channels. Along with line widths for these channels, a generalized asymmetric Fano line shape expression is obtained. It is found that while the ring diagrams contribute little numerically to the excitation spectrum in absolute terms, their retention is necessary to provide the asymmetry found in the ratio of experimental electron energy-loss spectrum of metallic cerium to lanthanum. \newline \newline [1] K. Nuroh, Phys. Rev. B 66, 155126 (2002). \newline [2] K. Nuroh, Phys. Rev. B 70, 205115 (2004).