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MA: Fachverband Magnetismus

MA 24: Terahertz Spintronics I

MA 24.3: Vortrag

Mittwoch, 20. März 2024, 10:00–10:15, EB 202

Observing terahertz orbital-angular-momentum currents with giant relaxation length in tungsten — •Tom Sebastian Seifert — Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin

Terahertz emission spectroscopy (TES) is a powerful tool to reveal photocurrent dynamics with femtosecond time resolution [1]. An exciting application for TES arises in the emerging field of orbitronics that exploits the electron orbital momentum L for possible data-processing applications [2]. However, direct experimental observation of L currents, their extended propagation lengths and their conversion into charge currents has remained challenging. Here, we optically trigger ultrafast angular-momentum transport in Ni|W|SiO2 thin-film stacks [3]. The resulting terahertz charge-current bursts exhibit a marked delay and width that grow linearly with the W thickness. We consistently ascribe these observations to a ballistic-like L current from Ni through W with a giant decay length (80 nm) and low velocity (0.1 nm/fs). At the W/SiO2 interface, the L flow is efficiently converted into a charge current by the inverse orbital Rashba-Edelstein effect, consistent with ab initio calculations. Our findings establish orbitronic materials with long-distance L transport as possible candidates for future efficient and ultrabroadband orbitronic terahertz emitters, and an approach to discriminate Hall-like and Rashba-Edelstein-like conversion processes.
[1] Leitenstorfer, A., et al., J. Phys. D 56(2023).
[2] Go, D., et al., EPL 135 (2021).
[3] Seifert, T.S., et al., Nat. Nanotechnol. 18, (2023).

Keywords: Orbitronics; Terahertz emission spectroscopy