Birefringence-like spin transport via linearly polarized antiferromagnetic magnons

Antiferromagnets (AFMs) recently demonstrate great potentials in efficient spin transport through magnons, providing a new platform for spintronics applications. Easy-plane AFMs, with two linearly polarized magnon eigenmodes that are orthogonal to each other, own unique advantages for low-energy control of ultrafast magnetic dynamics. However, it is commonly conceived that these magnon modes are less likely to transmit spins due to their vanishing angular momentum. In this work, we experimentally demonstrate that an easy-plane insulating AFM, α-Fe₂O₃ thin film, can conduct efficient spin transmission over micrometer distance. Remarkably, the spin decay length shows an unconventional temperature dependence that cannot be captured by solely considering thermal magnon scatterings. These observations are interpreted by the interference of two linearly polarized propagating magnons, a birefringence-like spin transport behavior. Finally, our devices can realize a bi-stable spin-current switch with a 100% on/off ratio under zero remnant magnetic field, providing additional opportunities for nonvolatile, low-field control of spin transport in AFM-based devices.