Theory of spin transport through an antiferromagnetic insulator

A theoretical formulation for spin transport through an antiferromagnetic (AF) insulator is presented in a case that is driven/detected by the direct/inverse spin Hall effect in two heavy-metal contacts. The spin signal is shown to be transferred by the ferromagnetic correlation function of the antiferromagnet, which is calculated based on a magnon representation. To cover the high-temperature regimes, we include an auxiliary field representing short AF correlations and a temperature-dependent damping due to magnon scattering. The diffusion length for spin is long, close to the degeneracy of the two AF magnons, and has a maximum as a function of temperature near the N\'eel transition.