Optical, electric and magnetic controlled ballistic conductance in monolayer WSe₂: the perfect valley and spin polarizations

Abstract

We study the charge and valley-spin ballistic transport through monolayer (ML) WSe2 potential barrier, of width and height , in the presence of an off-resonant light and ferromagnetic (FM) exchange field. We show that an electric switch is available in WSe2 by increasing beyond the critical value . Due to the band gaps of valley and responding differently to off-resonant light together with the huge spin–orbit coupling (SOC) in WSe2, the perfect valley and spin polarizations are obtained. Interestingly, under the effect of electrostatic potential , the valley polarization can be realized even for a tiny light intensity. Additionally, the FM exchange field can assist significantly the spin polarization in a wider region of light intensity and barrier height plane due to the large shift of spin-up and down bands. More important in our results, the highest valley and spin conductance is near 100% even under the polarized situation. These results demonstrate that WSe2 is a distinguished 2D material for novel spintronics and valleytronics in future.

A high-quality spin and valley beam splitter in WSe2 tunnelling junction through the Goos–Hänchen shift

“…When a positive U is applied, the Fermi energy of electron can be shifted downward and makes that the electronic transport is strongly affected by the gate. h is the FM exchange field generated through proximity effect of FM stripe [26,27], which can shift the spinup band downward and spindown band upward and yield spin sym metrybreaking [28]. I is the unit matrix.…”

Photo- and exchange-field controlled line-type resonant peaks and enhanced spin and valley polarizations in a magnetic WSe2 junction

“…Also, figure 1(b), shows the angles of incidence (θ) and reflection (ϕ). Here, the ML WSe 2 could be obtained through mechanical exfoliation [25,32] and the ferromagnetism in WSe 2 could be induced via the proximity effect [11,14,33,34] using EuO [35], EuS [36], CrI 3 [37], CrBr 3 [38], BiFeO 3 [39] or magnetic doping [40]. The gate voltage can be applied as a perpendicular electric field, that only tune the Fermi level without changing the topological phase [41].…”

“…One of the promising ways to control spin and valley degrees of freedom is the use of circularly polarized light, as reported in TMDs experimentally [6][7][8][9] and theoretically [10][11][12][13][14][15][16][17][18]. This is because such light carries finite orbital angular momentum which can thus couple to the spin degree of freedom via spin-orbit coupling (SOC).…”

“…Despite many studies in this field, the generation and manipulation of the high-efficiency spin-valley polarized transport in ML TMD junctions is still a very active field of research with many opportunities for new findings and results, due to its applications in spin/valleytronics devices. Qiu et al have studied the ballistic transport in a normal/ferromagnetic/normal (NFN) WSe 2 junction [14]. They found that an electric switch is available in the proposed junction by increasing the gate voltage beyond a critical value.…”

“…Compared to existing methods, i.e. magnetic [14], optical [15,16], and electric [26,27] modulation, manipulating the angle of electron incidence with the help of the off-resonance light or the exchange field, is a lesser-used knob to achieve significant spin-valley filtering. Unlike other 2D systems [28][29][30][31], the effect of incident angle on the transport properties of a WSe 2 junction has not been studied yet.…”