Microscopic analysis of relaxation mechanisms from energy- and time-resolved two-photon photoemission spectra of metal surfaces

Abstract

Microscopic theory of energy- and time-resolved (ER- and TR-) two-photon photoemission (2PPE) from metal surfaces is presented from the viewpoint of many-body dynamics of the electron system. The effects of hole dynamics in the occupied states at the surfaces are investigated by the nonequilibrium Green function method. In the macroscopic theory based on the density matrix method, it is usually considered that dephasing is due to elastic scattering and energy relaxation is due to inelastic scattering; however, it is demonstrated that inelastic electron–electron scattering of the photoexcited holes from the occupied states to the bulk can account for both dephasing and acceleration of energy relaxation. On the basis of analytical and numerical analyses for ER- and TR-2PPE on Cu(111), the relations of the macroscopic relaxation times with the electron and hole lifetimes are clarified.