Nondegenerate valleys in the half-metallic ferromagnet Fe/WS2

Abstract

We present a first principles investigation of the electronic properties of monolayer WS2 coated with an overlayer of Fe. Our ab initio calculations reveal that the system is a half-metallic ferromagnet with a gap of ∼ 1 eV for the majority spin channel. Furthermore, the combined effect of time-reversal symmetry breaking due to the magnetic Fe overlayer and the large spin-orbit coupling induced by W gives rise to non-degenerate K and K valleys. This has a tremendous impact on the excited state properties induced by externally applied circularly polarized light. Our analysis demonstrates that the latter induces a singular hot spot structure of the transition probability around the K and K valleys for right and left circular polarization, respectively. We trace back the emergence of this remarkable effect to the strong momentum dependent spin-noncollinearity of the valence band involved. As a main consequence, a strong valley-selective magnetic circular dichroism is obtained, making this system a prime candidate for spintronics and photonics applications.

Giant magnetoresistance control and nontrivial metallic state manipulation in a transition-metal dichalcogenide spin-valve using a gate voltage

“…Layered 2D materials, TMDC monolayer, have attracted great interest in recent years, owing to their unusual properties and the potential application in the field of highly effective information and high-density memory devices [1,3]. Although TMDC monolayer itself is not ferromagnetic, ferromagnetism in a TMDC monolayer has also attracted considerable attention due to the unique chance to acquire ferromagnetism via the doping and the proximity effect [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Via the magnetic proximity effect, if a TMDC monolayer is placed on a ferromagnetic substrate, the magn etic exchange potential of the substrate penetrates into the atomic layer, and a Zeeman field is introduced to the system.…”

“…The normal metal lead with RSOI extends from x = 0 to x = l. The FM region occupies x < 0 and x > l. The RSOI of the central lead can be engineered by applying an intentionally external gate voltage to the monolayer TMDC [23]. The FM region can be produced by doping [6][7][8][9][10] and proximity effect [14][15][16][17][18][19][20][21]. In this study, we focus on the case where the width (along y direction) of the TMDC, w, is much larger than l (w l).Thus the special description of the edges will become unimportant.…”

“…Actually, single-atomic-layer pristine TMDCs are direct band-gap semiconductor and not ferromagnet. However, the ferromagnetism in the material has gained a huge focus because of the basic theoretical motivation and the potential application in spintronics [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Previous studies have shown that the routes toward ferromagnetism effect can be classified by their modes of origin, i.e.…”

“…On the other hand, by an external magnetic field, magn etic manipulation of valley pseudospin has been observed recently [11][12][13]. Moreover, another effective approach to hunting for the valley and spin splitting issue is the spin injection from a ferromagnetic electrode [14,15]. Equally important, decoration of the TMDCs surface with heavy metal substances such as Co, Fe, CrI 3 , EuS, or EuO has also been proposed to break the time-reversal symmetry [16][17][18][19][20][21].…”