Valley polarization in magnetically doped single-layer transition-metal dichalcogenides

Abstract

We demonstrate that valley polarization can be induced and controlled in semiconducting single-layer transition-metal dichalcogenides by magnetic doping, which is important for spintronics, valleytronics, and photonics devices. As an example, we investigate Mn-doped MoS 2 by first-principles calculations. We study how the valley polarization depends on the strength of the spin orbit coupling and the exchange interaction and discuss how it can be controlled by magnetic doping. Valley polarization by magnetic doping is also expected for other honeycomb materials with strong spin orbit coupling and the absence of inversion symmetry. The fields of electronics and spintronics require an active control and manipulation of the charge and spin degrees of freedom [1]. Valleytronics, on the other hand, is very new field that relies on the property that the conduction/valence bands have two or more minima/maxima at equal energy but different momenta. For valleytronics devices it is necessary to induce valley polarization, i.e., control the number of electrons in each valley, typically by strain [2] or a magnetic field [3,4]. In general, two-dimensional materials have raised a lot of interest both for fundamental and applied reasons. Examples are semiconductor quantum wells [5], noble metal surfaces [6], graphene [7], and topological insulators [8]. Semiconducting single-layer transition metal dichalcogenides MX 2 with M = Mo, W and X = S, Se, Te and the D 3h point group have caught attention, because they display distinctively different physical properties as compared to their bulk compounds with the D 6h point group. There exists a crossover from an indirect band gap in multilayers to a direct band gap in the single-layer limit [9][10][11][12]. In the latter the conduction and valence band edges are located at the K points of the two-dimensional hexagonal Brillouin zone. These two inequivalent valleys constitute a binary index for low energy carriers, which gives rise to a valley Hall effect and valley dependent optical selection rules for interband transitions at the K points [13][14][15]. It has been demonstrated that optical pumping with circularly polarized light can achieve a dynamic valley polarization in single-layer MoS 2 [16][17][18]. However, from the application point of view an equilibrium valley polarization is desirable, which is the topic of the present paper.The interplay between spin orbit coupling and ferromagnetism in two-dimensional materials gives rise to a variety of unconventional phenomena, such as the quantum anomalous Hall effect [19][20][21][22]. In addition, it recently has been put forward that dichalcogenides doped with magnetic transitionmetal atoms form a promising platform for two-dimensional dilute magnetic semiconductors [23][24][25]. However, these studies did not take into account the spin orbit coupling, which interconnects the spin and valley physics. We propose in this paper a method to control the valley polarization by magnetic doping. Various possible Mn doping sites in single-l...

Electronic structures and magnetic properties in nonmetallic element substituted MoS2 monolayer

“…Actually, 2D MoS 2 ferromagnetic (FM) materials have been heralded as ideal candidates for the dilute magnetic semiconductors, which can exploit both the charge and spin degrees of freedom of the electron in one device [18], yielding remarkable properties and functionalities, in the field of spintronics. Besides the various magnetic properties induced by doping transition-metal [8][9][10][11][12][13]19,20], the adsorption of adatoms at the 2D monolayer MoS 2 have crucial effects on the electronic and magnetic properties [21,22]. The large spatial extensions of spin density and long-range antiferromagnetic (AFM) coupling were observed in H-and F-absorbed MoS 2 monolayers.…”

“…Since the successful cleavage of a monolayer molybdenum disulfide (MoS 2 ) from its three-dimensional (3D) bulk counterpart [1], massive research efforts also have been focused on the two-dimensional (2D) atomic crystals MoS 2 due to their great potential in applications, deriving from the optical [2], electronic [3,4], mechanical [5], and catalytic properties [6] of the materials. More recently, it has been demonstrated that valley polarization can be induced and controlled by using a circularly polarized light or by a magnetically doping in single-layer MoS 2 [7,8]. Diverse magnetic orderings have been reported recently in transition-metal-doped including Mn, Fe, Cu-doped MoS 2 [9][10][11][12][13].…”

Concepts of ferrovalley material and anomalous valley Hall effect

“…When the applied external fields including force, electric, magnetic or optical ones are removed, the system recovers to the initial paravalley state. For the purpose of applying in next-generation electronic products with nonvolatility, scheme by means of magnetic doping2324252627 appeared as an alternative approach. In consideration of the electronic transports suffering from impurity scattering, a more intelligent way using the magnetic proximity effect2829 is proposed very recently.…”

Nonlocal transistor based on pure crossed Andreev reflection in a EuO-graphene/superconductor hybrid structure

“…One major challenge to observe the rapid G CAR oscillation is the fabrication of a high-quality sample as the interface roughness and Fermi level fluctuations can wash out the oscillation. Finally, we point out that the pCAR mechanism proposed here is universally applicable to systems with similar band topology such as YiG-graphene [43] and monolayer transition-metal dichalcogenides with magnetic doping [44] or with proximity to EuO [45]. These structures offer alternative platforms to test the validity of our prediction.…”