Time-resolved two-photon photoemission from Cu(100): Energy dependence of electron relaxation

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Abstract
A time-domain measurement of the relaxation time of photoexcited electrons as a function of excitation energy at a single-crystal Cu(100) surface has been made with time-resolved two-photon photoemission. The relaxation lifetime of the excited electrons is found to decrease rapidly with the amount of excitation energy above the Fermi level, and we compare the measured lifetimes with a calculation based on Fermi-liquid theory. The results reveal a qualitative agreement with the theory, and indicate that effects due to transport of the electrons away from the surface and into the bulk are important.