Magnon spin Nernst effect (SNE) was recently proposed as a magnonic analog of the spin Hall effect, which takes place in layered collinear antiferromagnets such as MnPS₃. The magnon SNE extends many topological properties of electrons to magnonic systems where the bosonic statistics of magnons introduces unexpected physical consequences, opening a versatile platform for antiferromagnetic magnonics. However, existing studies all treated the magnon SNE as an intrinsic bulk effect, where spin diffusion and boundary spin transmission have been ignored. In real experiments, diffusion processes are essential to convert a bulk spin current into boundary spin accumulation, which then determines the spin injection into detectors through imperfect spin transmission. PI-Cheng’s group formulated a diffusive theory of the magnon SNE with boundary conditions reflecting real device geometry. It is found that in both electronic and optical detection, the actual output signals grow rapidly with an increasing system size in the transverse dimension until it eventually saturates. This provides crucial knowledge to experimentally benchmark and verify the magnon SNE in real antiferromagnetic materials. The diffusive theory also revealed that concerning symmetry properties, optical detection should be more reliable than electronic detection.

This work is published in Physical Review Applied, available here, and as an invited paper review in Applied Physics Letters, here.