Electronic Transport Properties And Quantum Confined Stark Effect In Mesoscopic Systems

The mesoscopic systems have attracted a lot of attention in recent years because of both the fundamental physics and the potential applications for future nanoelectronics. In this thesis, by making use of various theoretical methods, we investigate the electronic transport properties of several coupled quantum dot systems and quantum confined Stark effect in a rectangular quantum wire. Below we outline our works briefly.First, by means of non-equilibrium Green function technique, we investigated the electronic transport properties, such as the linear conductance spectrum and the I-V spectrum, in a side-coupled triple quantum dot array (QDA). With the increase of the dot-lead coupling, the multi-peak structure of the conductance spectrum changes into a structure with multiple conductance plateaus. In the range of conductance plateaus, the staircase step behavior of I-V spectrum disappears and the current is an approximate linear function of the bias voltage. When the intra-dot Coulomb repulsions are taken into account, the antiresonance valley in the conductance spectrum splits into three antiresonance valleys and the electron-hole symmetry of the conductance spectrum vanishes for the case of QDA with the sided coupled quantum dots. There is not split of the antiresonance valley in the conductance spectrum of the QDA without the sided coupled quantum dots. We discussed the feasibility of applying our structure to the electron spin polarized device and investigated the relation between the ratio of the spin polarized current flows and the bias voltage.Secondly, we investigated theoretically the persistent spin current and the persistent charge current in a semiconductor quantum-dot ring with the Rashba spin-orbit interaction. We found that a pure persistent spin current can be induced even in the absence of external magnetic flux and magnetic material. The magnitude and direction of the persistent spin current can be controlled experimentally by adjusting the energy levels of the quantum dots. Besides, the dot-lead coupling strength can influence the magnitude of the persistent spin current. We investigated the dissipation mechanism of the leads and the relation of the zero points of the persistent current and the resonant peaks of the linear conductance. When the geometrical symmetry of the system is destroyed, the pure persistent spin current still exists because the time-reversal symmetry of the system is maintained. Because the magnetic flux can break the time-reversal symmetry of the quantum-dot ring system, when a magnetic flux threads the quantum-dot ring, the persistent spin current can present with an accompanying persistent charge current. In addition, it is found that a certain spin component of the persistent currents can be suppressed by an appropriate external magnetic flux. When we consider the intra-dot Coulomb repulsions, the pure persistent spin current still exists.Thirdly, we investigated theoretically the inter-dot and Josephson current in a superconductor/quantum-dot ring/superconductor system by means of non-equilibrium Green’s functions technique in the Nambu representation. We found that a persistent current can coexist with Josephson current in this hybrid quantum-dot ring system when the values of superconducting phase difference and the magnetic flux in some regions. The magnitude and direction of the persistent current can be controlled experimentally by adjusting the quantum dot levels. In addition, the magnitude and sign of the persistent current in the quantum-dot ring can be manipulated by the phase difference of the two external superconducting leads because of the Andreev reflection process at the normal/superconductor interface.Finally, by means of the variational calculation method and effective-mass approximation, we have investigated the influence of the geometrical confinement and the effects on the transverse Stark effect in a rectangular quantum wire in the presence of an electric field. We obtained the asymptotic expansions of the Stark shift for low electric fields and for strong electric fields, respectively. We found that the Stark shift is a quadratic function of the electric field for low electric fields and is an approximate linear function of the electric field for strong electric fields. The Stark shift is influenced by the section figure of the quantum wire. Especially for high electric fields, the Stark shift is decided only by the size of the quantum wire in the direction of applied electric fields when the electric field is along the edge of quantum wire. In order to examine the validity of the variational wave function, we compared the results that obtained from the variational and the exact solution.