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].