Switch effect for spin-valley electrons in monolayer WSe2 structures subjected to optical field and Fermi velocity barrier

Abstract

To investigate the effects of the optical field and the Fermi velocity on the transport properties of spin and valley electrons, we impose a normal/ferromagnetic/normal (N/F/N) quantum structure based on the monolayer WSe2. The results indicate that there is a strong switch effect for spin- and valley-related electrons. When left-handed off-resonant circularly polarized light is irradiated in the intermediate ferromagnetic region, 100% polarization for K valley electrons can be achieved in the entire effective energy spectrum of the optical field. Meanwhile, 100% polarization of the K′ valley can also be gained with the right-handed off-resonant circularly polarized light in the junction. Moreover, the perfect polarization of spin-up electrons can be obtained when the ferromagnetic exchange field is applied to the structure. Additionally, the Fermi velocity barrier also changes the energy band of the studied material, which makes the spin and valley transport increase with the increase of the velocity barrier but does not produce spin or valley polarizations. These interesting results clarify that the optical field and the Fermi velocity both make a contribution to the modulation of spin electrons for the two valleys and provide a useful method for the design of novel spintronic and valleytronic devices.

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

“…As can be seen in figure 5(a) and also is confirmed by the band structure in figure 4(c), by increasing |h|, for h > 115 meV (h < −115 meV), only spinup (-down) band permitted to pass through the barrier, leading to fully spin polarization. The polarizations behavior for θ = 0 is in agreement with previous studies on WSe 2 [13,14], confirming our theoretical model. Similarly, it is seen in figure 5(b) and also is confirmed by figure 4 As can be seen in figures 5(a) and (b), in the case of θ = 0 there is no fully spin-valley polarization.…”

“…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).…”

Simultaneous perfect polarization of spin and valley using monolayer MoS2 modulated by light and spin Zeeman field

“…Moreover, in order to make the approximation to regard the time-dependent Hamiltonian as time-independent, the relationship |ev F A/ℏΩ| ≪ 1 needs to hold [34,36]. In our case, light with a wavelength of 50 nm can be used (Ω = 6000 THz), which will be able to produce a band gap of ∆ Ω2 = 0.03 eV when the intensity of light is 2 × 10 16 W m −2 [28,37].…”

Optically controlled valley-polarized resonance based on monolayer WSe2 electrical quantum structure

“…Regulation of optical filed can effectively change the properties of the material [19][20][21], thereby affecting the quantum transport. At present, there have been some works exploring the modulation of light on electronic structures [22][23][24][25][26][27][28][29][30][31]. In short, the presence of light has two necessary functions in electronic systems.…”

“…This study found that due to the adjustment of OCPL and the large spin-orbit coupling of WSe 2 , perfect valley-and spin-polarized currents are present. The group of Guo investigated the influence of OCPL and the Fermi velocity barrier on spin-and valley-polarized transport through the ML WSe 2 quantum junction [31]. The results indicate that there is a strong switch effect for spin-and valley-resolved conductance.…”