Terahertz field driven dynamics in metallic systems

One of the central challenges in modern solid-state physics is to understand how to coherently and nonlinearly manipulate charge carriers, their spin states, and orbital polarisation dynamics on ultrafast timescales using light fields. This problem is of profound interest both from a fundamental physics perspective and for future applications in next-generation quantum and optoelectronic technologies. Recent advances in nonlinear terahertz (THz) spectroscopy have opened new avenues to probe and control charge and spin dynamics in materials, enabling interconversion between these degrees of freedom at the speed of light.

In this colloquium, I will present my recent investigations into:

• nonlinear THz-driven charge carrier dynamics in Dirac materials [1-6],
• light-field-induced charge–spin interconversion in spin-active systems [7-9], and
• nonlinear responses in materials with strong spin–orbit coupling [10].

These studies offer new insights into ultrafast quantum control and reveal promising pathways for designing light-driven spintronic and electronic devices.

[1] H. Hafez et al., Extremely efficient terahertz high-harmonic generation in graphene by hot Dirac fermions. Nature 561, 507 (2018)

[2] J. Deinert et al., Grating-graphene metamaterial as a platform for terahertz nonlinear photonics. ACS Nano 15, 1145 (2021)

[3] S. Kovalev et al., Electrical tunability of terahertz nonlinearity in graphene. Science Advances 7, eabf9809 (2021)

[4] K. Tielrooij et al., Miliwatt terahertz harmonic generation from topological insulator metamaterials. Light: Science and Applications 11, 315  (2022)

[5] S. Kovalev et al., Terahertz signatures of ultrafast Dirac fermion relaxation at the interface of topological insulators. npj Quantum Materials 6, 84 (2021)

[6] P. Makushko et al., A tunable room-temperature nonlinear Hall effect in elemental bismuth thin films. Nature Electronics 7, 207 (2024)

[7] R. Salikhov et al., Coupling of terahertz light with nanometre-wavelength magnon modes via spin-orbit torques. Nature Physics 19, 529 (2023)

[8] I. Ilyakov et al., Efficient ultrafast field-driven spin current generation for spintronic terahertz frequency conversion. Nature Communications 14, 7010 (2023)

[9] R. Salikhov et al. Ultrafast unidirectional spin Hall magnetoresistance driven by terahertz light field. Nature Communications 16, 2249 (2025)

[10] R. Salikhov et al., Spin-orbit interaction driven terahertz nonlinear dynamics in transition metals. npj Spintronics 3,3 (2025)