Theory of electron- and photon-induced two-electron emission from surfaces

A short review is given of recent theoretical developments in (e,2e) and (gamma ,2e) spectroscopy from surfaces in reflection geometry. We first outline a general formal framework and currently viable approximations. Subsequently, a selection of numerical results demonstrates the quantitative agreement with experimental data, the extreme surface sensitivity of (e,2e), the imaging of a surface state dispersion, the influence of the Coulomb pair correlation between the two detected electrons, and the usefulness of spin-polarized primary electrons for the study of spin-dependent collision dynamics and of magnetic surface properties.