Speaker: Stefan Neppl, Lawrence Berkeley National Laboratory
Program Description
Time-resolved core-level photoemission has the exciting potential to provide electronic state- and atomic site-specific insight into fundamental electron dynamics at complex interfaces.
In the first part of the talk, I will discuss recent attosecond streaking experiments that address the ultrafast electronic motion inherent to the photoemission processes in condensed matter. In these measurements, sub-femtosecond XUV pulses are used to excite photoelectron wave packets inside a solid while their subsequent emission dynamics is sampled with the electric field of an optical laser pulse [1-3]. It will be shown that subtle time delays which develop during the release of electron wave packets from different energy levels of the solid can be resolved with a precision of only a few attoseconds (1 as = 10-18 s). For materials with a simple electronic band structure these time shifts can be intuitively interpreted as the real-time observation of photoelectrons propagating through the crystal lattice prior to their escape into vacuum [2,3].
In the second part, I will describe the implementation of femto- and picosecond time-resolved photoelectron spectroscopy at the LCLS and the Advanced Light Source with the goal to follow light-driven electron injection and recombination dynamics at dye-semiconductor interfaces on femto- to nanosecond timescales, and from the perspective of individual atomic sites [4,5].
[1] Cavalieri et al. Nature 449, 1029 (2007); [2] Neppl et al. Phys. Rev. Lett. 109, 087401 (2012); [3] Neppl et al. Nature 517, 342 (2015); [4] Siefermann et al. J. Phys. Chem. Lett 5, 2753 (2014); [5] Neppl et al. Faraday Discuss. 171, 219 (2014).
