Quantum Transport In Simple 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 some typical effects in mesoscopic transport including weak localization, Ahoronov-Bohm oscillation, universal-conductance fluctuations, and so on. Then provided is in the detail theoretical investigation of several practical models.First, Spin-polarization-dependent quantum transport through a quantum dot array coupled with two semi-infinite leads is investigated in terms of the tight-binding Hamilton which is spin-dependent due to external magnetic fields. By use of the transfer matrix method it is found that both the reflection and transmission probabilities display complex spectra. The total and relative transmissions are also investigated. It is also shown that the spin-currents of opposite spin-polarizations can be generated in different energy range.Secondly, the spin-polarized quantum transport through a T-shape quantum dot-array is studied. The transmission probabilities are shown to be tunable in a wide range by adjusting the energy and the direction angle of magnetic fields as well. Particularly the opposite-spin-polarization currents separately flowing out to two electrodes can be generated and thus the system acts as a pin splitter. Then, the quantum transport in a dot-array coupled with an AB ring is studied via single-band tight-binding Hamiltonian. It is shown that the output spin current is a periodic function of the magnetic flux in the quantum unitΦ₀.Moreover, the persistent currents in the AB ring is also spin-polarization dependent in difference from the isolated AB ring.Finally, we study the indirect-barrier quantum tunneling through a heterostructure of GaAs/AlAs/GaAs/AlAs/GaAs along the [001] axis. The X-Valley quasi-bound state gives rise to the Fano resonance in different from the direct double-barrier transition of the resonance-tunneling-diode type. We demonstrate with quantitative calculations that a relatively higher spin-polarization of the transmission probability can be achieved comparing with the single-barrier tunneling case. Further, the extension to the multi-barrier device is provided and leads to an important observation that the spin polarization increases with the number of barrier.