Probing ultrafast spin-orbitronic transport with terahertz electromagnetic pulses

To take advantage of the electron spin in future electronics, spin angular momentum needs to be transported and detected. Electric fields and temperature gradients have been shown to efficiently drive spin transport at megahertz and gigahertz frequencies. However, to probe the initial elementary steps that lead to the formation of spin currents, we need to launch and measure transport on much faster, i.e., femtosecond time scales. To achieve this goal, we apply optical femtosecond laser pulses to induce a spin voltage in metallic ferromagnets [1]. The resulting spin current into an adjacent layer is measured by conversion into a charge current and detection of the concomitantly emitted terahertz electromagnetic pulse [2]. Interesting applications such as terahertz spin-conductance spectroscopy [3] and the generation of ultrashort terahertz electromagnetic pulses emerge [4]. Finally, this principle can be transferred from the spin to the so far highly unexplored orbital angular momentum of electrons. We obtain new insights into orbitronic phenomena on their natural time scales, for example, time-domain signatures of giant propagation lengths of orbital currents in tungsten [5].

References

[1] Rouzegar et al., Physical Review B 106, 144427 (2022)
[2] Gueckstock et al., Advanced Materials 33, 2006281 (2021)
[3] Rouzegar et al., arXiv:2305.09074 (2023)
[4] Seifert et al., Nature Photonics 10, 483 (2016); Rouzegar et al., Physical Review Applied 19, 034018 (2023) [5] Seifert et al., Nature Nanotechnology (2023), https://doi.org/10.1038/s41565-023-01470-8