Intrinsic room-temperature piezoelectric quantum anomalous hall insulator in Janus monolayer $\mathrm{Fe_2IX}$ (X=Cl and Br)

Abstract

A two-dimensional (2D) material with piezoelectricity, topological and ferromagnetic (FM) orders, namely 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 Fe2IX (X=Cl and Br) with dynamic, mechanical and thermal stabilities is predict to be room-temperature PQAHI. At the absence of spin-orbit coupling (SOC), monolayer Fe2IX (X=Cl and Br) is a half Dirac semimetal state. When the SOC is included, these monolayers become quantum anomalous hall (QAH) states with sizable gaps (more than two hundred meV) and two chiral edge modes (Chern number C=2). It is also found that monolayer Fe2IX (X=Cl and Br) possesses robust QAH states against biaxial strain. By symmetry analysis, it is found that only out-of-plane piezoelectric response can be induced by a uniaxial strain in the basal plane. The calculated out-of-plane d31 of Fe2ICl (Fe2IBr) is 0.467 pm/V (0.384 pm/V), which is higher than or comparable with ones of other 2D known materials. Meanwhile, using Monte Carlo (MC) simulations, the Curie temperature TC is estimated to be 429/403 K for monolayer Fe2ICl/Fe2IBr at 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 QAH state. The combination of piezoelectricity, topological and FM orders makes monolayer Fe2IX (X=Cl and Br) become a potential platform for multi-functional spintronic applications with large gap and high TC . Our works provide possibility to use the piezotronic effect to control QAH effects, and can stimulate further experimental works.

Coexistence of intrinsic piezoelectricity and nontrivial band topology in monolayer InXO (X = Se and Te)

“…In fact, in our recent work, the PQAHI has also been achieved in Janus monolayer Fe 2 IX (X=Cl and Br) 31 , based on QAH insulator Fe 2 I 2 32 . Recently, the lithium decoration of layered iron-based superconductor materials FeX (X=S, Se and Te), namely LiFeX, are predicted as room-temperature QAH insulators with high Chern number (C=2) 33 , and the guidances on experimental realization have also been discussed.…”

“…It is well known that Janus monolayer MoSSe (S-Mo-Se) can be constructed from MoSe 2 with three atomic sublayers (Se-Mo-Se) 34 . In our previous work, the Janus monolayer Fe 2 IX (X=Cl and Br) is predicted to be PQAHI 31 determined by comparing the energy difference between antiferromagnetic (AFM) and FM states. The magnetic ground state of Li 2 Fe 2 SSe monolayer is FM, which can be seen from the (c) in Figure 1.…”

Designing light-element materials with large effective spin-orbit coupling

“…As a bonus, we systematically obtain nine materials with nontrivial SOC-induced bandgap (see Table I), rendering them large-gap QAH insulators against the thermal excitation [21] and local disorder [43]. While some materials in Table I, as well as certain artificial structures, are occasionally predicted as large-gap QAH insulators [44][45][46][47][48][49][50][51][52][53], the comprehensive understanding of the such over-room-temperature nontrivial gaps as well as systematic material search are still lacking. In our framework, however, the large-gap QAH insulators can be well understood and exhaustively collected from our material candidates (Supplementary Table S4) by performing more delicate GGA+U Wannier-representation tight-binding calculations [54][55][56][57] (see Methods).…”