Microscopic analysis of relaxation mechanisms from energy- and time-resolved two-photonphotoemission 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 theelectron system. The effects of hole dynamics in the occupied states at the surfaces areinvestigated by the nonequilibrium Green function method. In the macroscopic theorybased on the density matrix method, it is usually considered that dephasing is due toelastic scattering and energy relaxation is due to inelastic scattering; however, it isdemonstrated that inelastic electron–electron scattering of the photoexcited holes from theoccupied states to the bulk can account for both dephasing and acceleration of energyrelaxation. On the basis of analytical and numerical analyses for ER- and TR-2PPE onCu(111), the relations of the macroscopic relaxation times with the electron and holelifetimes are clarified.