Intrinsic and Extrinsic Losses in Photoemission Spectra

We theoretically study the intrinsic and extrinsic effects in photoemission spectra excited from core and also extended levels in space. Starting from Calori???s formula written in terms of the total lesser Green???s function g<tot including electron???photon interaction B, we obtain useful formulas for the photoemission intensity by use of Keldysh theory and Hedin???s equations which allow us to obtain perturbation expansion with renormalized Green???s functions. The terms without the screened Coulomb interaction W' but in the second order of B describe the intrinsic (shake) effects: The lowest order term can be written by use of the photoelectron Dyson orbital fp??? and hole Dyson orbital gn (dressed oneelectron occupied orbital). Another useful expression written in terms of retarded Green???s function is obtained whose cumulant formula is important to explain multiple plasmon loss satellite peaks. In order to include short-range correlation, T-matrix approximation is introduced. To go beyond the sudden approximation, the higher order terms including W' have to be taken into account to describe the extrinsic losses because W' is responsible for inelastic scatterings during the photoelectron propagation in solids affected by the fluctuation potential ??vl. We can naturally discuss the interference between these two different losses.