Engineering antiferromagnetic topological insulator by strain in two-dimensional rare-earth pnictide EuCd_2Sb_2

摘要

Antiferromagnetic topological insulator (AFM TI) provides an important platform to explore prominent physical phenomena and innovative design of topological spintronics devices, but very few high-quality candidate materials are known especially in two dimensions with intrinsic magnetism. Here, we propose an intrinsic two-dimensional (2D) AFM insulator and present a strain-engineered topological phase transition that realizes the 2D AFM TI phase in EuCd_2Sb_2 with in-plane magnetization. On the basis of first-principles calculations, the bandgaps of EuCd_2Sb_2 quintuple layers (QLs) are identified to be tunable, and a bandgap closing and reopening process is revealed with a small critical tensile strain of 2%. With opened bandgap, the topologically nontrivial characteristics of strained EuCd_2Sb_2 QLs are confirmed by the direct calculation of the spin Chern number Cs, Z_2 topological invariant, and the nontrivial topological edge states. Remarkably, while the previously proposed magnetic topological states may be heavily deformed by fragile magnetism, the obtained 2D AFM TI phase is highly robust against magnetic configurations, including ferromagnetic and AFM coupling with both in-plane and out-of-plane directions. Our results, thus, not only reveal the high possibility for engineering the 2D AFM TI state but also provide a very promising platform to uncover the complex interaction between magnetism and topology.