The role of Auger decay in hot electron excitation in copper

The role of different excitation mechanisms in two-photon photoemission measurements of the hot electron population dynamics in copper is considered. The effective hot electron lifetimes derived from two-pulse correlation measurements with similar to 3.1-3.8 eV, 50 fs laser pulse excitation are different depending on whether the hot electrons are generated by interband d --> sp or intraband sp --> sp excitation (S. Pawlik M. Bauer, M. Aeschlimann, Surf. Sci. 377-379 (1997) 206). A proposed explanation is that the latter process actually occurs by the Auger recombination of long-lived d-band holes resulting in complex hot electron population dynamics involving this delayed generation process and decay by the electron-electron scattering [E. Knoesel, A. Hotzel, M. Wolf, Phys. Rev. B 57 (1998) 12812]. This proposal is tested by simulation of interferometric two-pulse correlation measurements on the low index surfaces of copper (Cu(111), (100), and (110)) by the optical Bloch equations. The lower limit for the d-hole lifetime due to the Auger recombination of 24 +/- 3 fs for modeling of how this generation process affects the hot electron population kinetics is established from the d-hole decoherence measurements at the X-5 point. Optical Bloch equation fits of the data show that at most < 10% of hot electrons at 1.4 eV are generated through a secondary generation mechanism, therefore Auger recombination cannot explain the anomalous hot electron population dynamics. (C) 2000 Elsevier Science B.V. All rights reserved.