Valley, as a new degree of freedom of electrons besides charge and spin, can be used to encode, transmit, store, and manipulate information [1-3]. By using various external methods, such as optical pumping, magnetic field, magnetic doping, and magnetic proximity effect, the valley polarization can be induced in materials for realizing practical valleytronic devices. Recently, ferrovalley materials, a system with intrinsic magnetic and valley characteristics, was proposed for 2H-VSe2 [4]. Compared to traditional valleytronic materials, the ferrovalley materials have potential to eliminate the limitations associated with external fields in inducing valley polarization. However, to date, most of the predicted ferrovalley materials possess in-plane magnetization, which impede the appearance of valley polarization in nature. The crucial challenge is to induce large perpendicular magnetic anisotropy to achieve spontaneous valley polarization in two-dimensional ferrovalley materials. The van der Waals heterostructure, constructed by isolated atomic layer by layer in a chosen sequence, can reveal unusual properties and phenomena. Here, using first-principles calculations, we find that A-type antiferromagnetic VSe2/CrI3 heterostructure can realize perpendicular magnetic anisotropy and spontaneous valley polarization for realizing anomalous valley Hall effect, while the magnetic anisotropy of VSe2 is in-plane. More interestingly, the electric-field-controlled valley states can be realized by capping a ferroelectric layer (In2Se3) on VSe2/CrI3. The half metal-to-semiconductor transition and turning off and on valley are achieved by switching the ferroelectric polarization. Our results of constructing ferrovalley/ferromagnetic and ferroelectric/ferrovalley/ferromagnetic two-dimensional van der Waals heterostrucutre to engineer electronic and valley states can be useful for developing low-dimensional spintronic and valleytronic devices.

Anomalous Valley Hall Effect in A type Antiferromagnetic Van der Waals Heterostructures

The Dzyaloshinskii-Moriya interaction (DMI) plays a tremendous role for fast domain wall motion and allows creation of magnetic skyrmions which are very promising for spintronic devices. A standard ingredient in such devices is an interface between ferromagnetic metal and heavy nonmagnetic metal (HM), where the HM provides large spin orbit coupling as the energy source to obtain strong DMI[1]; or using Rashba effect at interface between a light element and ferromagnetic metal [2]. However, using a single two-dimensional (2D) magnet to obtain DMI and create skyrmions is rare even though the discoveries of truly 2D magnets such as Cr2Ge2Te6 CrI3, VSe2, MnSe2 and Fe3GeTe2 etc. have opened up new opportunities for spintronic technology. We demonstrate that significant DMI can be obtained in a series of Janus monolayers of manganese dichalcogenides MnXY (X/Y = S, Se, Te, X ≠ Y) in which the difference between X and Y on the opposites sides of Mn breaks the inversion symmetry. In particular, the DMI amplitudes of MnSeTe and MnSTe are comparable to those of state-of-the-art ferromagnet/heavy metal (FM/HM) heterostructures. In addition, by performing Monte Carlo simulations, we unveil that at low temperatures the ground states of the MnSeTe and MnSTe monolayers can transform from ferromagnetic states with worm-like magnetic domains into the skyrmion states by applying an external magnetic field. At increasing temperature, the skyrmion states start fluctuating above 50 K before evolution to a completely disordered structure at higher temperature. The present results pave the way for new device concepts utilizing chiral magnetic structures in specially designed 2D ferromagnetic materials[3]. Moreover, we unveil that topological magnetism and its electric control can both be achieved in the two-dimensional (2D) magnetoelectric multiferroics. We verify that significant DMI can promote the stabilization of sub-10 nm skyrmion in 2D multiferroics with perpendicular magnetic anisotropy such as CrN monolayer. [4]

**References:**

[1] Hongxin Yang, André Thiaville, Stanislas Rohart, Albert Fert, Mairbek Chshiev, Physical Review Letters 115, 267210(2015) [2] Hongxin Yang, Gong Chen, Alexandre AC Cotta, Sergey A Nikolaev, Edmar A Soares, Waldemar AA Macedo, Kai Liu, Andreas K Schmid, Albert Fert, Mairbek Chshiev Nature Materials 17, 605 (2018) [3] Jinghua Liang, Weiwei Wang, Haifeng Du, Ali Hallal, Karin Garcia, Mairbek Chshiev, Albert Fert, Hongxin Yang Phys. Rev. B 101, 184401 (2020) Editors’ suggestion [4] Jinghua Liang, Qirui Cui, Hongxin Yang, Physical Review B 102, 220409 (2020) (R)

 Significant Dzyaloshinskii-Moriya Interaction in Two-Ddimensional Janus Structures and its Electrically Control in 2D Magnetoelectric Multiferroics

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Anomalous Valley Hall Effect in A type Antiferromagnetic Van der Waals Heterostructures

Significant Dzyaloshinskii-Moriya Interaction in Two-Ddimensional Janus Structures and its Electrically Control in 2D Magnetoelectric Multiferroics

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