Theoretical Study On Quantum Transport Properties Of Multi-treminal Coupled-quantum-dot Systems

Electron interference in quantum-dot systems plays a dominant role in the electronic transport process through a mesoscopic structure. Such as multiple quantum-dot systems provide a variety of Feynman paths to take part in the quantum interference. To study the electronic transport of coupled quantum-dot systems reveals the phenonmenon about resonance and antiresonance of their electron interference which will offer theoretic foundation for future nanoelectronical design. The future miniaturization of electronic devices has directed attention to the study of discrete structures. In this paper, by making use of the nonequilibrium Green's function technique, we investigated the quantum transport properties of multi-terminal coupled quantum-dot molecular bridge and a four-quantum-dot ring with two side-coupled long quantum-dot arrays systems theoretically. Below we outline our works briefly.We investigated quantum transport of multi-terminal coupled quantum-dot molecular bridge. Both Dyson equations and equations of motion method for Green functions are used to obtain the current formula. In numerically analysis, we investigate the variety of transmission probability T1α(ω) of different single quantum-dot energy level of QDs and inter-dot coupling amplitudes when the system decoupled as two terminal, three terminal and four terminal systems. The calculations reveal that the transmission probabilities display oscillation structures. The energy level of each dot and lead play crucial roles in the transport properties of the system. If the energy level of lead and the single quantum-dot are the same espically when the system exists suspended quantum-dot, there would be occurring "antiresonant" tunneling. In additional, the electron transport through incident lead could not completely entry into another lead, this called "backward wave".We investigated transport through a four-quantum-dot ring with two side-coupled long quantum-dot arrays. With the side-coupled arrays, we investigate the even-odd parity dependence of the transmission probability. Then we examine the influence of the single electron energy levels of QDs to the transport and the regularity of the occurrence of antiresonance. By numerically calculating the transmission probability, with all single quantum dot energy levels are the same, we find that the transmission spectrum exceeds slightly the range ofε0±2V0, because of the side-coupling QD arrays and an obvious even-odd behavior appears atε0:antiresonance appears when both side-coupled QD arrays consisting odd number of QDs. While for the case of the single electron energy levels of QDs in the ring being different from those of QDs in the side-coupled QD arrays, this even-odd parity is absent. Instead, antiresonance appears when the number of the QDs in each array together with the QD coupling to the array in the ring is integer times of three. Then, for the case of electron energy with the inter-dot coupling being different, the number of resonance and the zero position of antiresonance have been not changed, in the meantime, the different coupling states have play significant role on transmission probability.