Spin-polarized Electronic Transport Of The Quantum Dot Ring Embedded In The AB Interferometer

A semiconductor quantum dot (QD) is a quasi-zero-dimensional mesoscopic structure, which presents prominent quantum effect of the electronic transport properties. It is well known that quantum interference plays a dominant role in electronic transport through a mesoscopic structure. As a typical mesoscopic structure, coupled multiple QDs embedded in the Aharonov-Bohm (AB) interferometer provide a variety of quantum interference paths to take part in the quantum interference, which contains abundant physical phenomena and physical mechanisms. QD has the artificial controllable character. Thus far the manufactures of QD devices have gained remarkable development, which represents a major field of the development of the nanoelectronic devices. The spin properties of the electron in the QD play an important role in the transport process. Some scientific researches indicate that the two different states of the electronic spin can be as 1 and 0 of a quantum information unit, which can transact the quantum information. It is considered as the most expectable realization of the quantum computer. In contrast to a single QD, coupled multiple-QD structures possess more structural parameters to tune their electronic transport properties, which bring about many new physical effects. Exploring the physical mechanisms and rules of the new effects can supply physical models and provide theoretical validity in the device design for better properties.In this thesis we investigate the electron and spin transport through a quantum-dot-ring embedded in the AB interferometer theoretically, by means of the standard nonequilibrium Green's function techniques, thereby, some significative results are obtained. Below we outline our works briefly from two aspects:On one hand, we establish such a system: a coupled multiple QDs ring embedded in the AB interferometer with different geometric configurations, and numerically simulate the conductance spectra of the electronic transport through the system by the Anderson model Hamiltonian and the non-equilibrium Green's function method. Then, we theoreticaly investigate the decoupled states and antiresonance phenomena presenting in the electronic transport by the molecular orbital representation theory. We find that the symmetry of the system and the magnetic flux through the AB interferometer are two physical mechanisms which induce to decoupled states. Even-odd parity oscillations occurs in linear conductance spectra of such a highly symmetric geometric configuration, due to even or odd molecular state decoupling from the leads with tuning the structure parameters , i.e., the magnetic flux. Moreover, other structure parameters, i.e., the inter-dot coupling strength and the dot-lead coupling strength, can not affect the even-odd parity oscillations. These results provide a new model for the designing of the nano-device.On the other hand, we investigate the spin-polarized conductance and current through such a system: a 4-QD-ring is embedded in the AB interferometer symmetrically, a magnetic flux threads the AB ring and a Rashba spin-orbit interaction induced spin-polarized transport only exists in the QD embedded in one arm of the AB interferometer. We also theoretically study the quantum interference presenting in the electronic transport by the molecular orbital representation theory. The results show that the spin-polarized transport occurs periodical oscillations by tuning the magnetic flux and the Rashba phase factor, and the resonance peaks of one spin encounter with the antiresonance points of another spin when the system is in equilibrium. In linear regime, the different spin-dependent molecule states decouple from the leads, due to the Rashba phase factor adjusting the quantum interference. It is the physical mechanisms of the spin polarization. We can effectively control the spin polarization strength by tuning the structure parameters, i.e., the inter-dot coupling strength or the dot-lead coupling strength, which can provide theoretical validity in the device design for quantum bit. When a bias voltage is applied on the two leads, spin polarized current exists in the system. The different spin-polarized current can occupy dominant station by turns with tuning the bias and the appropriate structure parameters. The spin current and charge current can move in opposite directions driven by the bias. Thus, we can control the spin-dependent current to design a device of spin current filter. Furthermore, the negative differential conductance also exists in the I-V spectra of the system, which may be devised as high-frequency oscillator.