Regensburg 2025 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 57: Ultrafast Electron Dynamics I

O 57.1: Vortrag

Mittwoch, 19. März 2025, 10:30–10:45, H2

Imaging the subcycle dynamics of topological surface currents in two-dimensional momentum space — •Tim Bergmeier¹, Suguru Ito¹, Jens Güdde¹, and Ulrich Höfer^{1, 2} — ¹Fachbereich Physik, Philipps-Universität Marburg, Germany — ²Fachbereich Physik, Universität Regensburg, Germany

Angle-resolved photoemission spectroscopy (ARPES), combined with THz-electric fields and subcycle temporal resolution, offers unique capabilites to explore light-matter interaction on timescales faster than the oscillation of a lightwave. With this approach, it is possible to directly observe the dynamics of lateral Dirac currents along the surface of topological insulators, as well as the ultrafast buildup and dephasing of Floquet-Bloch states. However, so far the momentum resolution of such experiments was restricted to only 1-dimensional cuts within the surface momentum space.

Here, we present first results on the subcycle dynamics of surface currents resolving the full Dirac cone of Bi₂Te₃. In our recently established setup in Marburg, a 200 kHz laser system allows for MV/cm field strengths by parametric amplification of frequency-tunable THz-pulses in the range of 20-40 THz, together with optimal focussing at large angles of incidence inside of the UHV chamber by astigmatism compensation. Combined with ultrashort 400nm two-photon probe pulses (<15 fs) and a Scienta DA30 photoelectron analyzer, we are able to measure the whole 2D-momentum space with subcycle resolution.

Keywords: ARPES; Subcycle; THz; Topological Insulator