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Inner edge state with spin and valley degrees of freedom is a promising candidate for designing a dissipationless device due to the topological protection. The central challenge for the application of the inner edge state is to generate and modulate the polarized currents. In this work, we discover a new mechanism to generate fully valley- and spin–valley-polarized current caused by the Bloch wavevector mismatch (BWM). Based on this mechanism, we design some serial-typed inner-edge filters. By using once of the BWM, the coincident states could be divided into transmitted and reflected modes, which can serve as a valley or spin–valley filter. In particular, while with twice of the BWM, the incident current is absolutely reflected to support an off state with a specified valley and spin, which is different from the gap effect. These findings give rise to a new platform for designing valleytronics and spin-valleytronics. [ABSTRACT FROM AUTHOR]

Inspired by potential application prospects of spintronics and valleytronics, a novel heterobilayer Janus structure is designed by replacing the chalcogenide atomic layers in the original bilayer MoS2. Based on first-principles calculations, it is found that the SMoS/SeMoS structure exhibits a direct band-gap semiconductor and a typical type-II band alignment with longer carrier lifetime. The transition metal (TM) atom represented by V/Cr/Mn can be stably adsorbed on the heterobilayer Janus SMoS/SeMoS sheet and effectively introduce magnetic moments (m). The calculation results demonstrate that the most stable adsorption site of the TM atom is CX(A), and the TM (V/Cr/Mn) adatom modified SMoS/SeMoS system is converted into metal (V-) or half-metal (Cr/Mn-), respectively. Under the coupling of different indirect exchange interactions, the structure exhibits stable intrinsic anti-ferromagnetic interactions for V-SMoS/SeMoS and ferromagnetic ground state for Cr/Mn-SMoS/SeMoS, respectively, and the magnetic transition temperature (T c) reaches a high temperature or even room temperature. Moreover, the robust out-of-plane magnetocrystalline anisotropy energy ensures stable long-range magnetic order. Specifically, the combination of spin injection and strong spin–orbit coupling interaction effectively breaks the time-reversal symmetry, which leads to valley polarization of the system. Based on this, the biaxial strain can effectively regulate the electronic structure, magnetic properties and valley polarization of TM-SMoS/SeMoS nanosheets with double breaking of spatial-inversion and time-reversal symmetry. [ABSTRACT FROM AUTHOR]

An investigation is carried on a quantum system featuring a MoS 2 zigzag nanoribbon employing double magnetic barriers. This study aims to overcome a valley polarization limitation observed in systems using a uniform magnetic field or a single magnetic barrier. A magnetic field breaks the degeneracy of the K and K ′ valleys owing to the valley Zeeman effect, but reversing the direction of the magnetic field is required to invert the valley polarization. In a double magnetic barrier system, interplay between the Fano resonance (arising from the quantum interference between the continuum state of the magnetic barrier and the Landau level) and the resonant tunneling (arising from the quantum states between two barriers) indicates the potential for achieving selective spin and valley polarization by adjusting the strength and width of the magnetic barrier. This can enhance the degree of valley polarization and enable the existence of four distinct spin and valley currents. Obtaining full spin and valley polarization is shown with the optimized parameters of this system. The experimental realization of this system should enable the control of carrier valley and spin degrees of freedom in future devices. [Display omitted] • Three-band tight-binding model using three d orbitals (dx 2 , dx2−y2, and dz2) of Mo atoms. • Double magnetic barrier is used to enhance valley and spin polarization. • Resonant tunneling effect in the K valley and Fano resonance effect in the K ′ valley. • The MoS 2 zigzag nanoribbon system with double magnetic barriers along the same direction has great advantages compared with a single magnetic barrier. [ABSTRACT FROM AUTHOR]

Due to its inherent size and surface effect, the ferroelectric properties of two-dimensional ferroelectrics are very different from those of traditional bulk ferroelectrics. So far, two-dimensional ferroelectrics have been reported to have many properties, including bulk photoelectric effect, piezoelectric/pyroelectric effect, valley polarization and spin polarization. These properties either depend on ferroelectric polarization or couple with it for electrical control, which makes 2 D ferroelectrics suitable for multi-functional nano devices. At present, the research of two-dimensional ferroelectrics in theory, experiment and application is accumulating. This study briefly introduces these theories and methods. Then, the intrinsic and extrinsic origins of two-dimensional ferroelectrics are summarized respectively. Finally, the existing problems and development prospects of two-dimensional ferroelectrics are discussed. [ABSTRACT FROM AUTHOR]

Abstract We study the spin- and valley-dependent energy band and transport property of silicene under a periodic potential, where both spin and valley degeneracies are lifted. It is found that the Dirac point, miniband, band gap, anisotropic velocity, and conductance strongly depend on the spin and valley indices. The extra Dirac points appear as the voltage potential increases, the critical values of which are different for electron with different spins and valleys. Interestingly, the velocity is greatly suppressed due to the electric field and exchange field, other than the gapless graphene. It is possible to achieve an excellent collimation effect for a specific spin near a specific valley. The spin- and valley-dependent band structure can be used to adjust the transport, and perfect transmissions are observed at Dirac points. Therefore, a remarkable spin and valley polarization is achieved which can be switched effectively by the structural parameters. Importantly, the spin and valley polarizations are greatly enhanced by the disorder of the periodic potential.

Valleytronic devices in which both the encoding and processing of information are achieved by manipulating electronic valley degrees of freedom are drawing increasing interest. However, materials with sizable intrinsic valley polarization are currently very rare. Using first‐principles calculations, a promising 2D multiferroic CuCrP2Te6 monolayer with intrinsic valley and spin polarization is proposed. The valley splitting at the corners of the Brillouin zone (K and K′) with opposite Berry curvatures can be as large as 110.4 meV, which is quite promising for achieving an anomalous valley Hall effect. Moreover, such valley splitting can be tuned through different approaches, such as modulating the spin polarization and electric polarization and external strain. The interplay between valley and multiferroic properties reveled herein offers a unique strategy for the valleytronic device applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Valley and spin polarization appear in the WS 2 /SrRuO 3 interface. • Valley and spin polarization can be attributed to the interfacial proximity. • Doping type and conductivity can be modulated as strain releases. Abstract The electronic structures of monolayer WS 2 on top of bilayer SrRuO 3 (1 1 1) are studied by first-principles calculations with spin-orbital coupling. The electronic properties can be influenced by stacking patterns of WS 2 /SrRuO 3 (1 1 1) heterostructures. Meanwhile, the valley polarization can be induced in monolayer WS 2 due to the broken time-reversal symmetry by the proximity to bilayer SrRuO 3 (1 1 1). With particular stacking patterns, larger valley splitting of monolayer WS 2 obtained in A1, A3, A4 and A5 models is 11.2, 11.3, 11.1 and 11.1 meV, respectively. Moreover, with biaxial strains, the conductivity of monolayer WS 2 can be effectively modulated. The Fermi level moves to a higher energy by appling tensile strains. Then the conductivity of WS 2 is governed by the valley states. In addition, the mechanical strains can modify the valley polarization and band gap effectively, showing potential applications in spintronic and valleytronic devices. [ABSTRACT FROM AUTHOR]

We study the symmetry, magnetization, temperature and electrostatic gating effect on the selective spin-valley polarized transport through the zigzag silicene nanoribbon (ZSiNR) coupled to two ferromagnetic (FM) leads, which are supposed to be in either parallel (P) or anti-parallel (AP) configuration. The transport properties show evident even-odd behavior and are not affected by the zigzag-chain number N when |EF|M. When |EF|V0. As the temperature rises, the spin/valley dependent conductance and the spin-valley polarization are smoothed. The above results have potential applications in fabricating spin-valleytronic devices based on FM-normal-FM ZSiNR junctions. [ABSTRACT FROM AUTHOR]

We study spin and valley transport through a ferromagnetic/nonmagnetic/ferromagnetic (FNF) monolayer silicene junction in the presence of an electrostatic gate potential U and on-site potential difference Δ z in the nonmagnetic region. We theoretically demonstrate that away from the band gap (no spin and valley conductances), the spin and valley polarizations of the junction show an oscillatory behaviour with U but near to it, they almost show a linear dependence with U. These oscillations are due to the phase difference of the electron wavefunctions of the spin and valley-resolved conductances that lead to chiral nature of the quasi-bound states in silicene. In particular, we find that the amplitude and frequency of the spin and valley polarizations oscillations of the junction can be tuned by varying the electrostatic gate potential U and on-site potential difference Δ z . Furthermore, it is shown that by increasing the exchange energy h the amplitudes of the spin and valley polarizations oscillations suppress. Enhanced spin (valley) polarization and its control by means of the electrostatic gate potential U makes the nonmagnetic tunneling junction a suitable candidate for utilizing in valleytronics and spintronics applications. [ABSTRACT FROM AUTHOR]

We investigate the electronic transport in a silicene-based ferromagnetic metal/ferromagnetic insulator/ferromagnetic metal tunnel junction. The results show that the valley and spin transports are strongly dependent on local application of a vertical electric field and effective magnetization configurations of the ferromagnetic layers. In particular, it is found that the fully valley and spin polarized currents can be realized by tuning the external electric field. Furthermore, we also demonstrate that the tunneling magnetoresistance ratio in such a full magnetic junction of silicene is very sensitive to the electric field modulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The valley polarization (VP) of the H-Tl 2 O/CrI 3 heterostructure is observed in both the conduction and the valence band. • A large valley spin splitting (VSS) of 0.57 (0.58) eV at the K (K') points are shown in the conduction band. • The VP and the VSS can be manipulated by adjusting the interlayer spacing and the in-plane biaxial strains. We report the two-dimensional H-Tl 2 O/CrI 3 van der Waals (vdW) heterostructure as a promising valleytronic material and investigate its valley polarization and valley spin splitting manipulation using first-principles calculations. The H-Tl2O/CrI 3 heterostructure displays valley polarization both in the conduction and valence band at two valleys. Particularly, valley polarization can attain 14.95 meV at the conduction band. In addition, a large valley spin splitting of 0.57 (0.58) eV at the K (K') point is shown in the conduction band. With the manipulation of the interlayer spacing and in-plane biaxial strain, the valley polarization and valley spin splitting of the H-Tl 2 O/CrI 3 heterostructure follow the short-range effects of interfacial orbital hybridization, thus a nearly linear relationship is shown. Our work provides not only application prospects of the H-Tl 2 O/CrI 3 heterostructure nanodevices but also theoretical effective support for research and development of valleytronics. [ABSTRACT FROM AUTHOR]

We investigated the spin- and valley-dependent energy band and transport properties in ferromagnetic silicene superlattice with an off-resonant circularly polarized light. It is obviously found that the spin- and valley-dependent energy gap can be well tuned via the off-resonant circularly polarized light. Fully spin and valley-polarized can be realized in certain ranges of light intensity. What is particularly interesting is that by slightly adjusting the energy of the light field, the valley polarization can be suddenly reversed from 100% to -100%. Thus, our results are expected to be informative for switching devices related to valleytronics. • Spin and valley energy gaps can be tuned via the off-resonant polarized light. • Energy range of full spin polarization and full valley polarization is enhanced. • Perfect valley switch effect is achieved by only modeling circularly polarized light. [ABSTRACT FROM AUTHOR]

• We study spin- and valley-dependent transport properties in a MoS 2 superlattice. • The conductance without and with spin-flip can be controlled by a gate voltage. • The amplitude of the spin polarization is very sensitive to potential height. • In MoS 2 superlattice the perfect valley and spin polarized currents can be observed. • Direction of the spin and valley polarization can be easily switched. Using the transfer matrix method, the valley- and spin-dependent transport properties of a monolayer MoS 2 superlattice in the presence of the extrinsic Rashba spin–orbit interaction (ERSOI) are theoretically investigated. The presence of the extrinsic Rashba and intrinsic spin-orbit coupling in this superlattice enhanced the valley and spin polarizations. By adjusting the superlattice parameters or the ERSOI strength, the perfect valley and spin-polarized currents can be observed. The valley- and spin-dependent conductance can be manipulated by the ERSOI strength and the barrier height. Due to the presence of the direct band gap and ERSOI, the conductance has a gap with respect to the barrier height. Furthermore, it was found that the efficiency of the spin-inversion can be modulated via the ERSOI strength, the number of superlattice barriers, and the gate voltage. [ABSTRACT FROM AUTHOR]

We have theoretically investigated the spin- and valley-dependent transport properties in a silicene superlattice under strain, with extrinsic Rashba spin–orbit coupling. It is demonstrated that due to the extrinsic Rashba spin–orbit coupling, spin-inversion can be achieved. It is shown that the valley and spin polarizations increase with increasing the number of superlattice barriers, and the magnitude and sign of valley and spin polarizations can be tuned by strain and extrinsic Rashba spin–orbit coupling. It is also found that the spin polarization through this superlattice reaches a maximum value at 2% strain. In particular, the fully valley polarized current can be achieved by adjusting the strain strength. Image 10 • We study spin- and valley-dependent transport properties in a silicene superlattice. • Fully valley polarized current can be achieved by adjusting the strain strength. • The spin-inversion can be efficiently controlled mechanically. • The valley and spin polarizations increase with increasing the number of barriers. • The spin polarization reaches the highest value at ε = − 2 % or ε = 2 % ac. [ABSTRACT FROM AUTHOR]