Electronic Correlation Effects On Kondo Resonances In The T-Shaped Double Quantum Dots

Following the development of the technology related to the preparation of nano-particles and the demand from information technology, people hope to develop small size, high reliability, and highly integrated quantum devices. However, the continuous decrease of their size will bring a series of boundary and quantum effects. In order to develop electronic devices according to the principles of quantum mechanics, the influence of the Kondo effect(observed in quantum dot system) on the transport properties of mesoscopic systems has become an important topic in condensed matter physics. Nowadays, people spent a lot of effort to study T-shaped double quantum dot(DQD) systems coupling with ferromagnetic electrodes, its asymmetrical structure showing some unique properties: electrons can be differentiated as those passing through the center of quantum dots and others passing through side-coupled quantum dots. Thus, we can take this model as an ideal amphoteric impurity system to study the strong correlation effect. In previous studies, people discussed the influence of the Coulomb repulsive interactions within quantum dots(ignoring the inter-dot coulomb repulsion) on electronic and electronic spin-polarized transports. Therefore we need to investigate the influence of correlation effects(such as the inter-dot coulomb repulsion, the coupling strength, etc.) on the electronic density of states. In this thesis, we use the Hamiltonian of the amphoteric impurity model of Anderson, and solve it by means of the slave-boson mean-field approximation and motion equation method, which allow us to obtain the electronic density of states and transmissivity of centered quantum dots. Through the analysis of images obtained under different parameters, we discuss the influence of electronic correlation effects on the Kondo resonances. The results show that: Firstly, the Coulomb interaction has an important influence on the Kondo resonance of centered quantum dots. In the symmetric case, the Kondo resonance peak width become narrow with the increase of U, which suppresses the Kondo resonance. The reason is that the Coulomb interaction destroys the double occupancy of the electron, hindering the electron tunneling, which is an indirect Coulomb blockade. In the asymmetric case, when U<1.5, the Kondo resonance peak width becomes narrow with the increase of U, however, when U>1.5, its width becomes broader, which is a special change. Secondly, when U = 0, the Kondo resonance peak width becomes narrow with the increase of 20 E, which suppresses the Kondo resonance. In the case of U = 1.5, when 20 E <?2.0, the Kondo resonance peak width becomes narrow with the increase of 20 E, and becomes broader when 20 E >?2.0, which is also a peculiar change. Thirdly, the coupling strength between quantum dots in the weak coupling region almost does not affect the Kondo effect. After getting into the strong coupling area, the influence becomes significant, showing a narrow Kondo resonance peak and suppressing the Kondo resonance. Finally, the bias makes the peak position of the Kondo resonance shift, and the peak width change obviously. Because T-shaped DQD systems can contain single and double quantum dots, we have reason to believe that these properties have positive significance both in theory and applications.