Intrinsic room-temperature piezoelectric quantum anomalous hall insulator in Janus monolayer FeIX (X = Cl and Br).

A two-dimensional (2D) material with piezoelectricity, topological and ferromagnetic (FM) properties, namely a 2D piezoelectric quantum anomalous hall insulator (PQAHI), may open new opportunities to realize novel physics and applications. Here, by first-principles calculations, a family of 2D Janus monolayer FeIX (X = Cl and Br) with dynamic, mechanical, and thermal stabilities is predicted to be a room-temperature PQAHI. In the absence of spin-orbit coupling (SOC), the monolayer FeIX (X = Cl and Br) is in a half Dirac semimetal state. When the SOC is included, these monolayers become quantum anomalous Hall (QAH) states with sizable gaps (more than 200 meV) and two chiral edge modes (Chern number C = 2). It is also found that the monolayer FeIX (X = Cl and Br) possesses robust QAH states against the biaxial strain. By symmetry analysis, it is found that only an out-of-plane piezoelectric response can be induced by a uniaxial strain in the basal plane. The calculated out-of-plane d of FeICl (FeIBr) is 0.467 pm V (0.384 pm V), which is higher than or comparable with those of other 2D known materials. Meanwhile, using Monte Carlo (MC) simulations, the Curie temperature T is estimated to be 429/403 K for the monolayer FeICl/FeIBr at the FM ground state, which is above room temperature. Finally, the interplay of electronic correlations with nontrivial band topology is studied to confirm the robustness of the QAH state. The combination of piezoelectricity, topological and FM orders makes the monolayer FeIX (X = Cl and Br) become a potential platform for multi-functional spintronic applications with a large gap and high T. Our work provides the possibility to use the piezotronic effect to control QAH effects, and can stimulate further experimental works.