Single Carrier In The Dynamics Of Coupled Double Quantum Dot System

Only in late 20 years of last century, mesoscopic physics, one burgeoning subject of Condensed States Physics, quickly comes into being and becomes a new hotspot of the studies in Condensed States Physics. Because of the expecting widespread applications of mesoscopic devices in micro-electronics technology and integrate circuits and so on, more and more attention has been paid to the research of those in many countries. Quantum dot is a basic cell of quantum device. It is formed on the two dimensional electron gas by the technology of splitting gates. Inside the quantum dots the motion of the electron is confined, which possesses quantum trait. We study the dynamical characteristic of single electron in coupled-quantum-dot system in this thesis. Some typical effects including weak localization effect, universal conductance fluctuations, coulomb blockade effect, Ahoronov-Bolm effect, and integer and fractional quantum Hall effect have been introduced briefly in Chapter 1. In Chapter 2, the two dimensional electron gas in heterostructures and the state density of the low dimensional electron gas are presented. We introduce some important characteristic lengths such as Fermi length, mean free path, phase-relaxation length and so forth. We also give the conditions in which electrons transport ballistically and derive the basic Landauer ?B黷tike conductance formula in mesocopic physics. At last we introduce a method of how to form a quantum dot and present the basic character of quantum dot. In Chapter 3 we discuss the effect of electric field on the probability of electron in the two coupled-quantum-dot system. An electric field is applied which changes the symmetry of the system. It is proved that the electric field changes the probability of the electron in the two quantum dots compared to Abstract them without the electric field. It is also demonstrated that the probability of the electron is related to the orientation of the electric field. According to perturbation theory of degenerate state, in coupled-quantum- dot system of two quantum dots, one energy level in each isolated quantum dot corresponds to two splitting energy levels of the coupled-quantum-dot system of two same quantum dots. Chapter 4 is contributed to the probability of the electron in the two energy levels, and the effect of positive coupling coefficient and negative coupling coefficient on it is discussed. The dynamical characteristic of single electron in coupled-quantum-dot system of more than three quantum dots is investigated in Chapter 5. In our study, we first discuss the moving characteristic of single electron in the coupled-quantum-dot of system. We show that unless very strong coupling the electron can not completely tunnel from the first dot to the third dot. According to the above investigation we can draw conclusions as follow. 1. When an electric field perpendicular to the barrier layer of the coupled quantum dots is applied the electric potential energy will change the occupation probability. By controlling the direction and intensity of the electric field, we can adjust the time evolution of the electron occupation probability in the system. 2. According to perturbation theory for degenerate energy level, a system of two coupled quantum dots has two energy levels梥ymmetric state and anti- symmetric state. We show that the...