Spin Transport In Low Dimensional Mesoscopic Systems

The spin-polarized electronic transport through mesoscopic structure has become one of the majors of the rapidly developed spintronics. This paper is firstly devoted to explain semiconductor quantum well, superlattices and quantum dot, then introduce several methods for quantum transport, for example: Landauer-Buttiker formula, transfer matrix, scattering matrix and noneqilibrium green function technique, finally provided is in the detail theoretical investigation of several practical models.First, using the effective-mass approximation, Floquet theory and transfer method, we investigate the electron resonance transmission through a symmetric double-barrier structure with the Dresselhaus spin-orbit coupling and an oscillating field applied to the potential-well region. It is demonstrated by the numerical evaluations that Dresselhaus spin-orbit coupling eliminates the spin degeneracy and leads to the splitting of resonance peaks in the conductivity. With the increasing of the amplitude of the oscillating field, photon-mediated transport process occur, the number of the resonance peaks and the distance between the adjacent peaks can be controlled by adjusting the amplitude and the frequency of the external field, respectively. Moreover, it is shown that a high spin polarization of the photon-mediated transmission probability can be achieved in the case of narrow potential well with a small amplitude of the oscillating field, which may be useful in the tunable spin filters of high efficiency.Secondly, using the transfer matrix method, we investigate the electron transmission over multiple-well semiconductor superlattices with Dresselhaus spin-orbit coupling in the potential-well regions. Compared to single well or double well, the superlattice structure enhances the effect of spin polarization in the transmission spectrum. The minibands of multiple-well superlattices for electrons with different spin can be completely separated at the low incident energy, leading to the 100% spin polarization in a broad energy windows, which may be an effective scheme for realizing spin filtering. Moreover, for the transmission over n-quantum-well, it is observed that the resonance peaks in the minibands split into n-folds or (n-1)-folds depending on the well width and barrier-thickness, which is different from the case of tunneling through n-barrier structure. Then, using the standard nonequilibrium Green's function techniques, we investigate the spin-polarization dependent Andreev-reflection currents through a double Aharonov-Bohm interferometer with Rashba spin-orbit interaction. The spin polarization of currents can be adjusted by tuning the Rashba spin-orbit interaction strength, the magnetic flux, and the interdot coupling as well, which lead to the transport current of complete spin polarization (either spin up or down) in both cases, with or without the interdot coupling. However, the current of complete spin polarization can approach its maximum value only in the absence of the interdot coupling.Finally, we investigate the ferromagnetic leads and Rashba spin-orbit interaction induced spin-polarized Andreev-reflection current through four-terminal Aharonov-Bohm interferometer. Based on crossed Andreev-reflection and normal transport process, the right lead can collect electrons and holes of both spin-up and spin-down. By adjusting the polarization of ferromagnetic leads, magnetic flux, and Rashba spin-orbit interaction strength, we obtain pure-spin current without charge current formed by equal number of electrons and holes with the same spin orientation. This may be an effective scheme for realizing a spin injector.