Orbital transport in W revealed by THz spectroscopy

Orbitronics devices has attracted significant attention due to the potential for magnetization manipulation. Recent studies have demonstrated orbital polarization optically excited by femtosecond lasers in cobalt-platinum alloy ferromagnetic layers, which subsequently radiate terahertz waves through orbital-charge conversion. In this work, we show the interplay of multiple terahertz emission mechanisms from cobalt-platinum alloy/tungsten/magnesium oxide. We performed an analysis of transfer matrix method on the thickness dependence of tungsten and cobalt-platinum alloy, and find that terahertz emission predominantly originates from the contribution from orbital currents. It is shown that the orbital currents are converted into charge current via inverse orbital Hall effect in tungsten and inverse orbital Rashba-Edelstein effect at the tungsten/magnesium oxide interface. This work provides a common framework for understanding the interplay of light-induced spin and orbital currents in ferromagnetic/non-magnetic/oxide heterostructures.