Hot-electron dynamics in copper revisited: The d-band effect

Interferometric time-resolved two-photon photoemission is measured over an energy range of 0.5-3.2 eV and a temperature range of 33-300 K for cesiated low-index surfaces of copper. Reduction of the work function by alkali ato m adsorption makes it possible to study the coherent and incoherent electro n dynamics in energy regions where either intraband or interband excitation dominates. Since most of the energy of 3.08-eV photons is deposited in d-b and holes, the creation of hot electrons through the Auger decay of d holes is an important mechanism for delayed production of secondary hot electron s. Slow electron-hole pair decoherence at the d-band maxima imply a d-hole lifetime of 24 +/- 3 fs at the top of the d bands. The contribution of Auge r decay to the hot-electron production leads to non-exponential population dynamics for hot electrons below 1.5 eV, and a resolvable delayed rise belo w 0.65 eV. Surprisingly, the delayed secondary hot-electron production appe ars to be suppressed at low temperatures. The energy and temperature depend ent contribution of the d-hole decay explains some aspects of the seemingly anomalous hot-electron lifetimes at the intensity maximum of the d-band tw o-photon photoemission.