Signature of topological states in antiferromagnetic Sm-substituted Bi₂Te₃

An antiferromagnetic topological insulator has been predicted to be preserved by breaking both time-reversal symmetry and primitive lattice translational symmetry. However, the topological surface state has often been observed to disappear in an antiferromagnetic phase because the doped magnetic impurity acts as an extrinsic defect. In this study, we report the experimental signature of topological surface states coexisting with antiferromagnetic order in Sm-doped Bi₂Te₃. We fabricate single crystals of Sm_xBi_2-xTe₃ with x = 0.004, 0.010, and 0.025, where the Curie-Weiss law is satisfied at low temperatures but is violated at high temperatures due to the influence of the high energy states of J multiplets of Sm. For x = 0.025, e xotic physical properties are observed, such as the antiferromagnetic phase with the Néel temperature T_N = 3.3 K, multi-band Hall effect with two conduction channel, and anisotropic Shubnikov-de Haas oscillations. In the antiferromagnetic phase, we detect the signature of nontrivial topological surface states with surface electron density n_s = 7.9 × 10¹¹ cm^-2 and its high mobility μ_s = 2,200 cm²/Vs, compared to n_b = 2.0 × 10¹⁹ cm^-3 and μ_b = 2.3 cm²/Vs for bulk electrons. These observations suggest that Sm_xBi_2-xTe₃ is a candidate creating the new stage for the potential application of topological antiferromagnetic spintronics.