Seminars Archive

Dynamic screening probed by core-resonant double photoemission from surfaces

Abstract
The universal response of an electronic system upon a suddenly created core hole is predicted to occur on an attosecond time scale, but lacks an experimental demonstration. A core hole switches on a local potential and triggers a series of dynamic electron screening processes, such as the shake-up of the outer-shell electrons, plasmon excitations and the emission of Auger electrons. It is a well-known experimental fact that the 4p photoelectron lines for the elements ranging from Ag to Xe are exceptionally broad. This can be explained by a dynamic fluctuation between a continuous and discrete electron configuration. With coincidence spectroscopy, we demonstrate an extensive energy sharing between the Ag 4p photoelectron and the NVV Auger electron exceeding 10 eV. This energy width provides access to the time scale of the emission process. We convert this to a timescale of 60 as over which the fluctuations takes place. This value is fair agreement with the theoretical calculation of the timescale to fill an exchange-correlation hole. This shows that core-resonant double photoemission is a powerful tool to probe the ultra-fast dynamic screening processes in the very beginning of the photoemission process on an attosecond timescale.