Onsager reciprocal relation between anomalous transverse coefficients of an anisotropic antiferromagnet

Whenever two irreversible processes occur simultaneously, time-reversal symmetry of microscopic dynamics gives rise, on a macroscopic level, to Onsager's reciprocal relations, which impose constraints on the number of independent components of any transport coefficient tensor. Here, we show that in the antiferromagnetic YbMnBi$_2$, which displays a strong temperature-dependent anisotropy, the Onsager's reciprocal relations are strictly satisfied for anomalous electric ($\sigma^A_{ij}$) and anomalous thermoelectric ($\alpha^A_{ij}$) conductivity tensors. In contradiction with what was recently reported by Pan $et~al.$ [Nat.Mater. 21, 203 (2022)], we find that $\sigma^A_{ij} (H)= \sigma^A_{ji} (-H)$, and $\alpha^A_{ij} (H)= \alpha^A_{ji} (-H)$. This equality holds in the whole temperature window irrespective of the relative weights of the intrinsic or extrinsic mechanisms. The $\alpha^A_{ij}/\sigma^A_{ij}$ ratio is close to $k_B/e$ at room temperature, but peaks to an unprecedented magnitude of 2.9 $k_B/e$ at $\sim$ 150 K, which may involve nondegenerate carriers of small Fermi surface pockets.