Initial electron thermalization in metals measured by attosecond transient absorption spectroscopy

Understanding initial electron thermalization has relevance to both fundamental scientific knowledge and application to the construction of novel devices. In this study, attosecond transient absorption is used to directly measure initial electron thermalization times of 38 \ifmmode\pm\else\textpm\fi{} 8 fs, 15 \ifmmode\pm\else\textpm\fi{} 3 fs, 4.2 \ifmmode\pm\else\textpm\fi{} 1 fs, and 2.0 \ifmmode\pm\else\textpm\fi{} 0.3 fs for Mg, Pt, Fe, and Co, respectively. Through time-dependent density-function theory calculations, it is shown that the fast electron thermalization observed in Fe and Co is correlated with a strong local-field effect. We find that a simple analytical model can be used to calculate the initial electron thermalization time measured by the transient extreme ultraviolet absorption spectroscopy method performed here. Our results suggest that the most significant contributions to the initial electron thermalization times are the basic metal properties of the density of states volume available for scattering and screened electron interaction. Ultimately the information gained through this study shows the unique view that attosecond transient absorption spectroscopy contributes to unraveling and monitoring electron dynamics and its connection to many-body effects in metals and beyond.