Using the tight-binding formalism, we study spin and charge transport through a zigzag silicene ribbon subject to an external electric field E z . The effect of an exchange field M z is also taken into account and its consequences on the band structure as well as spin transport are evaluated. We show that the band structure lacks spin inversion symmetry in the presence of intrinsic spin-orbit interaction in combination of E z and M z fields. Our quantum transport calculations indicate that for certain energy ranges of the incoming electrons the silicene ribbon can act as a controllable high-efficiency spin polarizer. The polarization maxima occur simultaneously with the van Hove singularities of the local density of states. In this case, the combination of electric and exchange fields is the key to achieving nearly perfect spin polarization, which also leads to the appearance of additional narrow plateaus in the quantum conductance. Moreover, we demonstrate that the output current still remains completely spin-polarized for low-energy carriers even when a few edge vacancies are present.

The electronic structure and transport properties of monolayer MoS 2 are studied using a tight-binding approach coupled with the nonequilibrium Green's function method. A zigzag nanoribbon of MoS 2 is conducting due to the intersection of the edge states with the Fermi level that is located within the bulk gap. We show that applying a transverse electric field results in the disappearance of this intersection and turns the material into a semiconductor. By increasing the electric field the band gap undergoes a two stage linear increase after which it decreases and ultimately closes. It is shown that in the presence of a uniform exchange field, this electric field tuning of the gap can be exploited to open low energy domains where only one of the spin states contributes to the electronic conductance. This introduces possibilities in designing spin filters for spintronic applications.

We consider a three slabs configuration including two non-doped single layer graphene on insulating silicon dioxide (G/SiO2) substrates and one non-doped suspended single layer graphene (SG). The suspended layer is placed between two G/SiO2 layers. Without SG layer, the heat flux has maximum at Plasmon frequency supported by the G/SiO2 slabs. In three slabs configuration, the photon heat tunneling is amplified between two G/SiO2 layers significantly, only for specific range of vacuum gap between SG layer and G/SiO2 layers and Plasmon frequency, due to the coupling of modes between each G/SiO2 layer and SG layer. Since, the SG layer is a single atomic layer, the photon heat tunneling assisted by this configuration does not depend on the thickness of middle layer and in consequence, it can enable novel applications for nanoscale thermal management.

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We study topological phase transitions and topological quantum field effect transistor in monolayer molybdenum disulfide (MoS) using a two-band Hamiltonian model. Without considering the quadratic (q ) diagonal term in the Hamiltonian, we show that the phase diagram includes quantum anomalous Hall effect, quantum spin Hall effect, and spin quantum anomalous Hall effect regions such that the topological Kirchhoff law is satisfied in the plane. By considering the q diagonal term and including one valley, it is shown that MoS has a non-trivial topology, and the valley Chern number is non-zero for each spin. We show that the wave function is (is not) localized at the edges when the q diagonal term is added (deleted) to (from) the spin-valley Dirac mass equation. We calculate the quantum conductance of zigzag MoS nanoribbons by using the nonequilibrium Green function method and show how this device works as a field effect topological quantum transistor.

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We study perfect valley polarization in a molybdenum disulfide (MoS 2 ) nanoribbon monolayer using two bands Hamiltonian model and non-equilibrium Green's function method. The device consists of a one-dimensional quantum wire of MoS 2 monolayer sandwiched between two zigzag MoS 2 nanoribbons such that the sites A and B of the honeycomb lattice are constructed by the molecular orbital of Mo atoms, only. Spin-valley coupling is seen in energy dispersion curve due to the inversion asymmetry and time-reversal symmetry. Although, the time reversal symmetry is broken by applying an external magnetic field, the valley polarization is very small. A valley polarization equal to 46% can be achieved using an exchange field of 0.13 eV. It is shown that a particular spin-valley combination with perfect valley polarization can be selected based on a given set of exchange field and gate voltage as input parameters. Therefore, the valley polarization can be detected by detecting the spin degree of freedom.

We consider a double-stranded DNA molecule connected to non-magnetic and magnetic (nickel (Ni) and iron (Fe)) leads and study its spintronic properties using tight binding non-equilibrium Green function method. By considering the combination of the spin-orbit coupling, the environment-induced dephasing, and the helical symmetry, it is shown that although the hopping parameter of spin up electrons is higher than spin down electrons for both Ni and Fe leads, the spin up (spin down) current is significantly higher than spin down (spin up) current when the lead is Ni (Fe) and for non-magnetic leads the difference is not high with respect to magnetic leads, i.e., there should be a matching process rule between leads and dsDNA. Also, we show that by applying an AC electric (gating) field perpendicular to helix-axis, the spin current is approximately zero at half period and will be maximized for specific gate voltage at other half period and therefore dsDNA habits as a field effect transistor (FET). It is found that there are both p-channel and n-channel FET and the logical cell can be designed theoretically. We think that the results of present paper could motivate further experimental studies on DNA spintronics.