Spin-Polarized Transport Property Of The Mesoscopic Systems

In this work, we have made a detailed investigation of the spin polarized transport properties through mesoscopic systems, which owns great potential application in future electronic devices. Our aim is to explore the physical mechanisms of the new effects in mesoscopic systems; and on the other hand, to supply physical models and provide theoretical validity in the device design for better properties. After a brief review of some important theoretical and experimental developments in mesoscopic systems, and also a relatively detailed introduction of the method used in this work-nonequilibrium Green's function theory, this dissertation is devoted to theoretical investigation of several interesting transport-devices.First, we propose, theoretically, a new type of design that generates the spin-polarized current through a mesoscopic device composed of lateral double-quantum-dot in the company of time oscillating and spin-polarization dependent tunneling. A formula for the spin-dependent current is obtained to discuss the transport properties. We demonstrate that the spin and charge currents are controllable by adjusting the gate voltage, the frequency of driving field and the magnitude of the magnetic field as well. In particular an in- teresting resonance phenomenon of the spin current is qualitatively explained in terms of the exact solutions of a time-dependent Schrodinger equation for an electron moving between the two quantum dots.Then, we investigate the spin-current and its shot-noise spectrum in a single-molecule quantum dot coupled with a local phonon mode. We pay special attention to the effect of the phonon on the quantum transport property. The spin-polarization-dependent current is generated by a rotating magnetic field applied in the quantum dot. Our results show the remarkable influence of phonon mode on the zero-frequency shot noise. The electron-phonon interaction leads to sideband peaks that are located exactly at the integer number of the phonon frequency, and moreover, the peak height is sensitive to the electron-phonon coupling.Finally, Based on the infinite-U Anderson model spin-polarized transport through the tunnel magnetoresistance (TMR) system of single-molecule quantum dot with two ferromagnetic leads is investigated under the interplay of strong electron correlation and electron-phonon (e-ph) coupling. The spectral density and the nonlinear differential conductance is calculated using an extended equation of motion approach. It is observed that the transport properties are similar with the previous results for the antiparallel magnetic configuration of electrodes, while for the parallel case both the Kondo-resonance peak and the phonon-induced satellite-peaks split up into two asymmetric peaks of lower height. Correspondingly, the nonlinear differential conduc- tance displays a set of symmetric satellite-peaks around the Kondo-peak in the large e-ph coupling region. Increase of the e-ph coupling leads to an overall decrease of the conductance resonance-peaks. Furthermore, extra maxima and minima appear in the TMR curve vs bias-voltage resulted by the e-ph interaction. The TMR alternates between the positive and the negative values along with the variation of polarization and bias voltage. While the positive value of TMR increases markedly with the increase of polarization. The peculiar TMR line-shape observed here may serve as a more effective tool to explore the Kondo-resonance features in practical systems.