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

Abstract

Manipulating the valley degree of freedom as an information carrier has been a focused topic for both fundamental and applied research. Here, using first-principles calculations, we report the identification of monolayer CrX 2 (X=S, Se) as a novel two-dimensional valleytronic crystal. It shows large valley spin splitting in the valence band, attractive for the integration of valleytronics and spintronics. More importantly, through proximity coupling with monolayer CrCl 3 , the valley polarization in monolayer CrX 2 is achieved, which can be further engineered by stacking patterns. Also, the valley polarization in monolayer CrX 2 can be obtained via magnetically doping V and Mn. Specially for V-doped monolayer CrSe 2 , there are no impurity states in the band gap, beneficial for its practical applications. Our works thus provide not only exceptional two-dimensional valleytronic crystals but also promising ways for realizing valley polarizations in them.

Structural deformation and mechanical response of CrS2, CrSe2 and Janus CrSSe

“…These TMDs mainly exhibit three poly-type according to their atomic arrangement, namely, H -phase (hexagonal), T -phase (tetragonal), and T' -phase (distorted). Following the literature [17,20,38], we have chosen H-phase, which is energetically favorable among all these three phases. The hexagonal honeycomb CrX 2 structure consists of one Cr (bonded with 6 nearest X atoms) layer sandwiched between two S or Se atoms such that hexagonal symmetry can be seen from the top view.…”

“…Unlike graphene and many other 2D materials, the in-plane asymmetry in TMDs provides them with extraordinary thermoelectric and optoelectronic properties [15,16]. Particularly, chromium-based TMDs like CrS 2 and CrSe 2 show unique properties such as valley polarization in band structure [17], piezoelectric coupling, and phase-dependent intrinsic magnetic properties [18]. For example, a previous report shows that CrS 2 nanosheet has the potential to use as negative electrodes in lithiumion batteries that could be promising for high-power energy storage [19].…”

“…In addition, the thermal and mechanical properties of Cr-based TMDs are promising materials when they are engineered in heterostructure form [10]. Plus, the CrS 2 and CrSe 2 are two exceptional 2D valleytronic crystals with large valley spin splitting in the valence band [17].…”

Intrinsic Valley Polarization in Computationally Discovered Two‐Dimensional Ferrovalley Materials: LaI2and PrI2Monolayers

“…Due to breaking of the inversion symmetry in a monolayer, several 2D hexagonal systems have shown to exhibit two or more degenerate DOI: 10.1002/adts.202100476 valleys at inequivalent K and K points in the Brillouin zone, such as 2D transitionmetal dichalcogenides, Janus monolayers, and graphene. [1][2][3][4][5][6] Because of the large separation between the K and K points in the reciprocal space, these valleys are robust against any intervalley scattering induced by deformation or long wavelength phonons. Since the two valleys are degenerate in energy due to the presence of timereversal symmetry in a non-magnetic system, utilization of valley degree of freedom requires breaking the degeneracy so that the valleys at K and K can be distinguished and manipulated separately.…”

Electronic Properties of Monolayer and van der Waals Bilayer of Janus TiClI

“…In the case of Cr-and V-doped TiClI ML, the obtained valley polarization is quite close to that of V-doped CrS 2 (40.4 meV), 33 and Vdoped MoSSe (59 meV), 34 but much larger than those of Crdoped MoSSe (10 meV) 34 and Cr-doped WSSe (3 meV). 35 It should be pointed out that if the valley polarization is obtained by applying an external magnetic field mentioned above, the magnetic field should be at least 230 T to obtain such a large valley polarization in Cr-doped TiClI ML. 36 It is of course a challenge to achieve such a large external magnetic field in practice, strongly suggesting that magnetic doping is an effective and promising method to realize the valley polarization in the Janus TiClI ML.…”