Negative Magnetoresistance in Antiferromagnetic Topological Insulator EuSn_2As_2^*

The measurements of magnetization, longitudinal and Hall resistivities are carried out on the intrinsic antiferromagnetic (AFM) topological insulator EuSn_2As_2. It is confirmed that our EuSn_2As_2 crystal is a heavily hole doping A-type AFM metal with the Néel temperature T_\rm N = 24 K, with a metamagnetic transition from an AFM to a ferromagnetic (FM) phase occurring at a certain critical magnetic field for the different field orientations. Meanwhile, we also find that the carrier concentration does not change with the evolution of magnetic order, indicating that the weak interaction between the localized magnetic moments from Eu^2+ 4f^7 orbits and the electronic states near the Fermi level. Although the quantum anomalous Hall effect (AHE) is not observed in our crystals, it is found that a relatively large negative magnetoresistance (-13%) emerges in the AFM phase, and exhibits an exponential dependence upon magnetic field, whose microscopic origin is waiting to be clarified in future research.