Ultrafast coherent magnon spin currents in antiferromagnets

TL;DR

This paper demonstrates that ultrafast coherent superpositions of magnon pairs in antiferromagnets can generate controllable spin currents, including circular ones, using linearly polarized light, advancing ultrafast spintronics.

Contribution

It introduces a method to produce net spin currents from magnon pairs in antiferromagnets via superposition, a novel approach in ultrafast magnonics.

Findings

Coherent superpositions produce net spin currents in antiferromagnets.

Linearly polarized light controls the spin current direction.

Superposing orthogonal currents yields circular spin currents.

Abstract

Generating coherent magnon spin currents with the highest frequencies and shortest wavelengths is a key challenge in ultrafast spintronics and magnonics. A promising route is to excite counter-propagating magnon pairs. In antiferromagnets, such pairs can be accessed in the ultrafast regime, where coherent dynamics are dominated by magnons at the edge of the Brillouin zone. However, it has seemed impossible to generate a net spin current from coherent magnon pairs. Here we show that a coherent superposition of multiple magnon-pair modes can produce such a current in parity-time symmetric antiferromagnets. The ultrafast coherent spin currents are excited with linearly polarized light, with the light polarization steering the current direction. Finally, by superposing two orthogonal spin currents, circular spin currents can be generated, which have not been discussed for steady-state currents.