High-speed antiferromagnetic domain walls driven by coherent spin waves

The ability to rapidly manipulate domain walls in magnetic materials is key to developing novel high-speed spintronic memory and computing devices. Antiferromagnetic materials present a particularly promising platform due to their robustness against stray fields and their potential for exceptional domain wall velocities. Among various proposed driving mechanisms, coherent spin waves could potentially propel antiferromagnetic domain walls to the magnon group velocity while minimizing dissipation from Joule heating. However, experimental realization has remained elusive due to the dual challenges of generating coherent antiferromagnetic spin waves near isolated mobile antiferromagnetic domain walls and simultaneously measuring high-speed domain wall dynamics. Here we experimentally realize an approach where ultrafast laser pulses generate coherent spin waves that drive antiferromagnetic domain walls and develop a technique to directly map the spatiotemporal domain wall dynamics. Using the room-temperature antiferromagnetic insulator Sr₂Cu₃O₄Cl₂, we observe antiferromagnetic domain wall motion with record-high velocities up to ~50 km s^-1. Remarkably, the direction of domain wall propagation is controllable through both the pump laser helicity and the sign of the domain wall winding number. This bidirectional control can be theoretically explained, and numerically reproduced, by the domain wall dynamics induced by coherent spin waves of the in-plane magnon mode-a phenomenon unique to magnets with an easy-plane anisotropy. Our work uncovers a novel domain wall propulsion mechanism that is generalizable to a wide range of antiferromagnetic materials, unlocking new opportunities for ultrafast coherent antiferromagnetic spintronics.