The Electron Dynamics And Transport Properties In The Coupled Double-Quantum-Dot System

In this dissertation, the generalized Hubbard model, which describes the double-quantum-dot system, is introduced by the canonical quantization method. Its Hamiltonian includes not only the normal Josephson tunneling and Coulomb interaction terms, but also the terms which indicate the exchange of electrons and the tunneling of electron pairs. Then, based on this generalized Hubbard model, the charges stability diagram, the electron dynamics and the transport properties of the double quantum dot are investigated. The following are the main contents and results:(1) The influence of quantum effect on classical charge stability diagram is studied. The single electron and electron-pairs tunneling make the boundaries of hexagonal configuration in the classical charge stability diagram become smooth, and the tunneling of electron pairs only affect the boundaries of two-electron-occupied regions. The hexagonal configuration is not changed by the electron exchange effect.(2) The effects of resonant tunneling and localization of two electron state in double quantum dot is discussed. When the energy levels in two quantum dots are resonance, the Josephson tunneling couple induces the periodical oscillating evolution of probabilities occupied on different two-electron configuration in double quantum dot. The Coulomb interaction changes both the oscillating frequency and amplitude while the electron pairs tunneling breaks down the properties of periodical evolution. When the energy levels in two quantum dots are detuned, the localization of the electron depends on the initial state of the system due to the Coulomb interaction and electron pair tunneling. If two electrons with opposite spin are in one of quantum dots initially, they will stay there as the system is evolving. But if two electrons are in different quantum dots, they will not be local in the initial state.(3) The effects of electron pair tunneling on the current and noise is studied by the method of quantum rate equation. When the system is completely symmetrical, the variation curves of both current and the shot noise with the bias voltage are symmetric about zero value of bias voltage. Fano factor is sub-Poissonian in the whole bias region. The electrons pair tunneling can make the step positions and values of the current and Fano factor change. When the system is asymmetrical, the variation curves of current and shot noise are not symmetric about zero bias voltage. With the increasing of the couple asymmetry, the absolute value of the current decreases, while the Fano factor increases. In certain bias voltage, the negative differential conductance and the super-Poissonian shot noise appear and the electron pair tunneling make them increase.