Antiferromagnets (AFMs) have the potential to push spintronic devices from the static or gigahertz frequency range to the terahertz (THz) range for the sake of the high-speed processing. However, the insensitivity of AFMs to magnetic fields also makes it hard to manipulate spin currents. While the ultrafast generation of the spin current in ferromagnet/heavy metal (FM/HM) structures has received a lot of attention in recent years, it is still unknown as to whether a similar scenario can be observed in an AFM/HM system. Here we show the optical generation of ultrafast spin current in an AFM/HM heterostructure at zero external magnetic field and at room temperature by detecting the associated THz emission. We believe this is a common phenomenon in antiferromagnets with strong nonlinear optical effects. Our results open an avenue of fundamental research into antiferromagnetism and a route to AFM spintronic devices.
 Qiu et al., Ultrafast spin current generated from an antiferromagnet, Nature Physics, 17, 388 (2021).