We propose a graphene nanoribbon pumping device and study its quantum charge and spin pumping properties for both adiabatic and non-adiabatic regimes by using the Keldysh non-equilibrium Green's function and renormalization procedure. We show that the adiabatic regime is suitable for the generation of high charge current, while the non-adiabatic regime is appropriate for the generation of fully spin polarized and pure spin currents. Also, it is shown that the proposed device can act as a perfect and controllable spin filter. Moreover, we investigate the effects of width and edge of graphene nanoribbons and show that the pumped charge current in the zigzag graphene nanoribbon (ZGNR) strongly depends on nanoribbon width so that the maximum pumped current for width with even numbers of carbon chains is about one order of magnitude larger than that with odd numbers. In contrast with ZGNR, in armchair graphene nanoribbon, the pumped currents with even and odd numbers have the same order of magnitude.
We study spin-resolved electron transport in a double quantum ring in the presence of Rashba spin-orbit interaction and a magnetic flux using quantum waveguide theory. We show that, at the proper values of the system parameters such as the Rashba coupling constant, the radius of the rings, and the angle between the leads, the double quantum ring can act as a perfect electron spin-inverter with very high efficiency. Also, the double quantum ring can work as a spin switch. The spin polarization of transmitted electrons can be controlled and changed from −1 to +1 by using a magnetic flux.
Articles you may be interested inInduced spin-accumulation and spin-polarization in a quantum-dot ring by using magnetic quantum dots and Rashba spin-orbit effectIn this paper, spin-filtering properties of transmitted electrons through a quantum ring in the presence of Rashba spin-orbit interaction and magnetic flux are studied. To investigate the effects of coupling between the leads and ring on the spin-filtering, the S-matrix method is used. It is shown that by tuning the Rashba spin-orbit strength and the magnetic flux, the quantum ring can act as a perfect spin-filter with high efficiency. The spin-filtering can be changed from spin up to spin down and vice versa by changing the Rashba strength when the magnetic flux is held constant or by changing the magnetic flux when the Rashba strength is held constant. In addition, the effect of the angle between the leads on spin-filtering properties is taken into account and the angles at which the spin-filtering can occur are determined. The spin-filtering can take place in narrow ranges of electron energy for weak coupling, while for strong coupling it can take place in a wide range of electron energy. V C 2013 American Institute of Physics. [http://dx.
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