First-Principles Prediction of a Room-Temperature Ferromagnetic Janus VSSe Monolayer with Piezoelectricity, Ferroelasticity, and Large Valley Polarization

Abstract

Inspired by recent experiments on the successful fabrication of monolayer Janus transition metal dichalcogenides [Nat. Nanotechnol. 12 (2017) 744] and ferromagnetic VSe 2 [Nat. Nanotechnol. 13 (2018) 289], here we for the first time predict a highly stable room temperature ferromagnetic Janus monolayer (VSSe) by ab initio evolutionary and density functional theory methods. Monolayer VSSe exhibits a large valley polarization due to the broken space and timereversal symmetry. Moreover, the low symmetry C3v point group of VSSe monolayer results in giant in-plane piezoelectric polarization. Most interestingly, a strain-driven 90° lattice rotation is occurred in magnetic VSSe monolayer with an extremely high reversal strain (73%), indicating an intrinsic ferroelasticity. The combination of multiferroic, piezoelectricity, and valley polarization will render magnetic 2D Janus VSSe for potential applications in nanoelectronics, optoelectronics and valleytronics.

High-temperature ferromagnetic semiconductors: Janus monolayer vanadium trihalides

“…[35][36][37][38] For example, It has been found T C of Janus monolayer VSSe reaches as high as 400 K and the stability is comparable with its pristine VSe 2 . 39,40 Also utilizing the strategy, some novel stable FM semiconductors have been predicted such as Janus monolayer X 3 -Cr 2 -Y 3 . 41…”

Valley polarization in monolayer CrX2 (X = S, Se) with magnetically doping and proximity coupling

“…This results in a large amount of intriguing phenomena and potential applications, especially in information storage and processing [12][13][14][15]. Although 2D valleytronic materials are highly desirable, up to now, only a few candidates are proposed, including graphene, VSSe, Tl 2 O, and 2D transition metal dichalcogenides (TMDs) MX 2 (M=V, Ta, Mo, W; X=S, Se, Te) [16][17][18][19][20][21][22]. Therefore, new 2D valleytronic materials remain to be discovered and are still urgently needed.…”

Two-Dimensional Ferroelastic Semiconductors in Nb2SiTe4 and Nb2GeTe4 with Promising Electronic Properties

“…The recent interest in 2D ferroelastic crystals not only lies in ferroelasticity itself but also extends to the coupling of ferroelasticity and electronic properties. [11][12][13][14] Compared with 2D crystals presenting ferroelastic order only, undoubtedly, 2D crystals that hold ferroelasticity and intriguing electronic properties simultaneously are more desirable as they will open up unprecedented opportunities for developing multifunctional and controllable devices. Currently, there are mainly two types of such coupling in 2D crystals.…”

“…17 Examples mainly include BP5, Janus VSSe, silver and copper monohalides. 7,12,17 Another is the coupling between ferroelasticity and nontrivial topology. 18 In our previous work, we proposed that single-layer 1S'-MSSe (M = Mo, W) is a 2D ferroelastic topological insulator and holds appealing potential for controlling the anisotropy of the topological edge state via ferroelastic switching.…”