Seminarium MTPR - Prof. Ralph Ernstorfer

Speaker: Prof. Ralph Ernstorfer (Technische Universität Berlin, Germany)

Link to the MSTeams meeting

This year’s Nobel Prize in Physics is awarded to Pierre Agostini, Ferenc Krausz, and Anne L’Huillier for the generation of attosecond light pulses. I will give a brief review of the technological development enabling the underlying process of high-harmonic generation and the birth of attosecond science as a new research field. I will discuss how ultrashort pulses in the extreme ultraviolet spectrum enable the investigation of the fastest electronic processes in crystals. Starting with the technique of attosecond streaking, I discuss how the intrinsic duration of the photoemission process can be resolved [1]. On the basis of this enabling technology, high-harmonic generation advanced a range of other spectroscopic techniques, especially time- and angle-resolved photoemission spectroscopy (trARPES. We advanced the technique to access all key properties of many-body states like excitons with multidimensional photoemission spectroscopy. I will exemplify these approaches for excitons in transition metal dichalcogenide semiconductors [1]. In addition, we studied excitons in molecular crystals and investigated the singlet-exciton-fission process in the molecular crystal pentacene and revealed the hybrid-orbital character of the singlet state as well as the disputed mechanism of the fission process [2].

References

1. S. Neppl et al., Direct observation of electron propagation and dielectric screening on the atomic length scale, Nature 517, 342 (2015).
2. S. Dong et al., Direct measurement of key exciton properties: Energy, dynamics, and spatial distribution of the wave function, Natural Sciences 1, e10010 (2021).
3. A. Neef et al., Orbital-resolved observation of singlet fission, Nature 616, 275 (2023).

Chairman: Prof. Jacek Gapiński