The Electron And Spin Properties Of Quantum Dots

Semiconductor quantum dot (QD) is a quasi-zero-dimensional mesoscopic structure, which presents discrete electron energy spectrum and strong electron interaction. Because of such electronic characteristics, a single QD is viewed as an artificial atom. Accordingly, a structure consisting of several coupled QDs confines electrons in a way as an artificial molecule. In contrast to a single QD, multiple QD structures possess more structural parameters to tune their electronic transport properties. Therefore, the investigations on the multiple QD structures are the current focus in the field of mesoscopic physics. In this thesis we report our theoretical investigations about the electron and spin transport through parallel double QD structure, by means of non-equilibrium Green function technique, thereby, some interesting results are obtained. Below we outline our works briefly from two aspects:On the one hand, the Coulomb-induced changes of electronic transport through a double quantum dot ring are discussed. For the linear-transport case, the variation of Coulomb interaction in the reference channel QD can remarkably modify the sign of the Fano parameter, which lead to the change in Fano interference, including the increase or decrease in the symmetry of the Fano lineshape, as well as the inversion of the Fano lineshape. When both the QD levels are adjustable, the Coulomb-induced splitting of the reference channel induces the destruction of Fano interference. As for the nonlinear electron transport, the Fano lineshape emerge in the differential spectra when the resonant-channel QD levels is adjusted to the vicinity of the chemical potential of either lead, expect for the case where it encounters the reference-channel QD level. The presented Coulomb interactions also play a nontrivial role in the appearance of the negative conductance and capacitance.On the other hand, By means of the nonequilibrium Green function technique, spin transport through a three-terminal parallel double-quantum-dot structure is theoretically studied, with the application of a local Rashba spin-orbit coupling. We find that an incident electron from the source can select a specific drain to depart from the quantum dots according to its spin state, as a result, spin polarization and spin separation can be simultaneously realized in this structure. The influence of the intradot Coulomb interaction on the electron tunneling is studied in detail. It is interesting that the change of the electron interaction in the quantum dot coupled to the additional lead gives rise to nontrivial variation of conductance.