Effect of Coulomb Interactions between Photoexcited Electrons and Holes on Time-Resolved Two-Photon Photoemission from a Metal Surface

The effect of Coulomb interactions between photoexcited electrons and holes on time-resolved two-photon photoemission from a metal surface is investigated with the aid of a simple model where the electron system consists of an sp-band, a d-band and free electron states above the vacuum level. A formula for the correlation trace (photoelectron intensity as a function of the pump-probe delay time) is derived by perturbation theory based on the Liouville equation and by treating Coulomb interactions within the Hartree-Fock approximation. It is demonstrated on the basis of the obtained results how Coulomb interactions affect the correlation trace.