Freitag, 02. Juni 2017, 15:15 - 16:45 iCal

Seminar Physikalische Chemie und Materialchemie

Dr. Peter Kraus (University of California Berkeley): "Attosecond kinetics of photoexcited Germanium"

Universität Wien, Fakultät für Chemie, Seminarraum 2, Raum 2124
Währinger Straße 42, 1090 Wien


The electronic motion in a semiconductor after light absorption is a central aspect of modern opto-electronics. However, a real-time observation of the initial electronic response following single-photon excitation has so far defied experimental approaches due to its extreme time scales.

Here, attosecond transient reflectivity in the extreme ultraviolet is developed. The technique is applied to measure attosecond carrier dynamics at the germanium core-level transition following carrier promotion by visible-to-infrared sub-5 femtosecond (fs) pulses from the valence into the con-duction band in single-crystalline germanium. The buildup of holes and electrons in the valance and conduction band is monitored on attosecond timescales by the change in the reflectivity at the germanium M4,5 edge (30 eV).

In the presented experiments, a finite sub-10 fs response time following photoexcitation, visible as an initial broadening of the observed reflectivity changes (panel a), is observed. Additionally, a field-driven transient population buildup, synchronized with the oscillations of the driving electric field, is identified (panel b).

Similar electronic responses after photoexcitation are anticipated to occur in all materials. The time scales involved will limit the ultimate speed of charge transfer in metal complexes, charge separations in photovoltaic cells and phase transitions in strongly correlated materials. The results presented here thus provide an experimental measurement of the fundamental timescales of charged particle interactions in solids.


Institut für Physikalische Chemie, Universität Wien


Univ.-Prof. Dr. Wolfgang Kautek
Universität Wien
Institut für Physikalische Chemie
0043 664 60277 52470