Tom Seifert

---

The native time and length scales of interactions between electrons, spins, and the lattice in solids reside typically in the nanometer and femtosecond domain. To resolve the resulting non-equilibrium dynamics in quantum materials, ultrafast optical probes must overcome the diffraction limit imposed by far-field optics. In this talk, I will present terahertz (THz) nanoscopy as a powerful tool that enables simultaneous femtosecond temporal and nanometer spatial resolution.
I will first discuss THz-emission spectroscopy, showing how this sensitive far-field probe provides novel insights into femtosecond transport dynamics in spinorbitronic heterostructures (including 2D materials), the multiferroic BiFeO3, and the topological insulator Bi2Se3 [1-3]. Then, I will demonstrate how the combination of THz-emission spectroscopy with a near-field probe allows for the direct filming of ultrafast spintronic transport at the nanoscale.
I will conclude by outlining a promising path to extend THz nanoscopy toward atomic resolution. This approach aims to enable local coherent control and read-out of quantum matter [4-6] on femtosecond time scales, bridging the gap between macroscopic transport and atomic-scale dynamics.

References
[1] T. S. Seifert et al., Nature Photonics 10, 483 (2016)
[2] T. S. Seifert et al., Nature Nanotechnology 18, 1132 (2023)
[3] C. In, D. Jain, T. S. Seifert, …, T. Kampfrath, ArXiv preprint, arXiv:2601.01030 (2026)
[4] T. S. Seifert et al., Science Advances 6, eabc5511 (2020)
[5] V. Rai, J. Sim, F. Faaber, N. Bogdanoff, S. Trishin, P. Wiechers, T. S. Seifert, …, K. J. Franke, Science Advances 11, eadz6549 (2025)
[6] T. Siday, …, R. Huber, Nature 629, 329 (2024)

---

Freie Universität Berlin
PH2
Contact: Erwann Bocquillon / Matteo Cacco