We develop a low-temperature, long-wavelength theory for the interfacial spin Seebeck effect (SSE) in easy-axis antiferromagnets. The field-induced spin-flop (SF) transition of N\'eel order is associated with a qualitative change in SSE behavior: Below SF, there are two spin carriers with opposite magnetic moments, with the carriers polarized along the field forming a majority magnon band. Above SF, the low-energy, ferromagnetic-like mode has magnetic moment opposite the field. This results in a sign change of the SSE across SF, which agrees with recent measurements on Cr2O3/Pt and Cr2O3/Ta devices [Li et al.,Nature578, 70 (2020)]. In our theory, SSE is due to a N\'eel spin current below SF and a magnetic spin current above SF. Using the ratio of the associated N\'eel to magnetic spin-mixing conductances as a single constant fitting parameter, we reproduce the field dependence of the experimental data and partially the temperature dependence of the relative SSE jump across SF.
@article{arxiv.2003.05232,
title = {Spin Seebeck Effect near the Antiferromagnetic Spin-Flop Transition},
author = {Derek Reitz and Junxue Li and Wei Yuan and Jing Shi and Yaroslav Tserkovnyak},
journal= {arXiv preprint arXiv:2003.05232},
year = {2020}
}