paper

Time-domain observation of ballistic orbital-angular-momentum currents with giant relaxation length in tungsten

arXiv:2301.00747 · doi:10.1038/s41565-023-01470-8

Abstract

The emerging field of orbitronics exploits the electron orbital momentum . Compared to spin-polarized electrons, may allow magnetic-information transfera with significantly higher density over longer distances in more materials. However, direct experimental observation of 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|SiO thin-film stacks. The resulting terahertz charge-current bursts exhibit a marked delay and width that grow linearly with W thickness. We consistently ascribe these observations to a ballistic current from Ni through W with giant decay length (~80 nm) and low velocity (~0.1 nm/fs). At the W/SiO interface, the 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 ballistic transport as possible candidates for future ultrafast devices and an approach to discriminate Hall- and Rashba-Edelstein-like conversion processes.

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