Image of an electron and a laser wave passing through each other

Attosecond Atomic and Solid-State Physics – Theory

Main research areas: Time-resolved electronic dynamics in atoms, molecules, and solids, theory of time delays and electron transport

Our research in the area of Advanced Photon Science focuses on the theory of the interaction of attosecond pulses with atoms, surfaces, and solids. Progress towards generation of ultrashort pulses on a time scale comparable to that of electronic dynamics opened up unprecedented opportunities: matching the time scales and electronic motion and pulse duration allows one to monitor, control, and shape both electrons and electromagnetic wavepackets.

One focus of current research is the theory of attosecond chronoscopy. Chronoscopy addresses timing as a fundamental observable. Prototypical applications include the photoelectric effect and the information time-resolved photoemission can reveal of the underlying complex systems from which photoemission originates. The helium atom represents one of the most important prototypical strongly correlated electron systems. Ionization by the attosecond XUV pulse allows to monitor time-resolved multi-electron dynamics. The time delay of the emitted electron carries information on the corelated motion. We have recently shown by ab-initio simulations that delays offer novel insights into quantum entanglement on ultrashort time scales (Fig. 1).

Streaking spectrograms for time-resolved correlated electron emission from helium (Jiang et al., Phys.Rev.Lett. 133, 163201 (2024) — **Figure 1:** Streaking spectrograms for time-resolved correlated electron emission from helium (Jiang et al., Phys.Rev.Lett. **133**, 163201 (2024)

**Figure 1:** Streaking spectrograms for time-resolved correlated electron emission from helium (Jiang et al., Phys.Rev.Lett. **133**, 163201 (2024)

Attosecond chronoscopy also enables access to information on the bandstructure and electron transport in condensed matter. In collaboration with the experimental groups at TU Munich and MPQ Garching we have recently demonstrated that bandgaps in the high-energy continuum of graphene-related layered materials can be observed through modulations of the photoemission time delay. Key is the direct relation between time delay and modulation of the density of states of a quantum system which we have established for attosecond streaking (Fig. 2).

**Figure 2:** Simulation of the relative streaking delay Dt between p-electrons and s-electrons of the HOPG valence band as a function of excitation energy compared with experimental data for acceptance angles 2° (red crosses) and 22° (blue dots). (Potamianos et al., Sci. Adv. 10, eado0073 (2024))

**Figure 2:** Simulation of the relative streaking delay Dt between p-electrons and s-electrons of the HOPG valence band as a function of excitation energy compared with experimental data for acceptance angles 2° (red crosses) and 22° (blue dots). (Potamianos et al., Sci. Adv. 10, eado0073 (2024))

Other topics of current interest in our group are the theoretical description of high-harmonic generation in solids with the focus on the influence of decoherent dynamics on the harmonic spectra and the coherent conduction-band electron dynamics driven by strong few-cycle infrared pulses.