Attosecond electron dynamics in Dirac materials and tunneling junctions

Attosecond science (1 attosecond = 10^-18 s) is based on the control of electron motion by the field waveform of intense ultrashort laser pulses. In our lab, we apply field waveform control to investigate signatures of many-body electron dynamics of bulk solids, nanostructures and molecules on ultrafast time scales. In a first experiment [1], we study ultrashort electron dynamics in highly oriented pyrolytic graphite (HOPG), which retains much of the Dirac physics of monolayer graphene. We find a surprisingly strong carrier excitation effect near the Dirac point, which leads to a suppression of the emission of higher harmonic light. Our experiment is able to track the underlying excitation dynamics and suppression caused by internal state blocking. In a second research avenue, we integrate a conventional scanning tunneling microscope (STM) with an ultrafast femtosecond laser in order to achieve electron microscopy with extreme spatial and temporal resolution. We demonstrate attosecond control of the electric current in the nanoscale STM tunneling junction using the waveform of the laser field. We also introduce a strong-field model which explains the physics of ultrafast STM currents [2]. Our innovation promises simultaneous ångström and attosecond observations of plasmonic dynamics and ultrafast many-body phenomena in organic molecules.

[1] Z. Chen et al., manuscript under review in Nature Photonics, preprint arXiv:2505.24290 (2025).

[2] B. Ma and M. Krüger, Phys. Rev. Lett. 133, 236901 (2024).