Electron Transport Properties Of Mesoscopic Nano-system

Mesoscopic nano-systems are forefront in condensed matter physics. There existing in these systems a great deal of novel and marvelous physics properties and prospective potential applications. In this thesis, we study the electron transport properties of mesoscopic nano-system by using the Green's function method. The aim is to explore the physical mechanisms of the found new effects in these systems, and to supply physical models and theoretical validity in designing novel quantum devices with better properties.The thesis consists of eight chapters. In chapter one, we introduce typical structure of mesoscopic nano-systems and their characteristics, especially their transport properties.In chapter two, the Green's function method is simply introduced. By applying the method, we calculate the electron transport properties of T-shaped quantum wires under potential modulation. The influence of potential modulation in vertical quantum wire on electronic transport across one or two-coupled T-shaped quantum wire(s) is discussed. For a single T-shaped quantum wire, the potential induces a dip-peak couple structure in the conductance curves for parallel and bend transport. The change of the potential thickness induces the dip-peak couple more pronounced. For two coupled T-shaped quantum wires, two dips in the parallel conductance are associated with the potential modulation. Conductance profiles can be tailored by the modulation.In chapter three, we calculate the bound state energies and wave functions of crossed, T-shaped, L-shaped quantum wire and quantum dot under potential modulation by using mode-match method. The relation of the bound state energy and the potential height for different structures is found. The contour plots of the probability density visualize the evolution of the bound state in different structures. The calculation to the lifetime of bound states in quantum dot indicates that there is an evolution of eigenstate in quantum dot from a bound state to a quasibound state and then to a bound state.In chapter four, the resonant peaks via the quasibound states in the confined array of antidots are studied. We calculate the conductance of several structures, and discuss the influence of the distance between antidots on the bound states and electron transport. The influence of the period of antidot array on the higher-energy bound states is also discussed. Some interesting higher-energy bound states are found, electrons in the states are not localized at the junctions but at the intersections of the junctions.In chapter five, we calculate the conductance of two typical open periodic structures. For the periodic multiwaveguide structure including n constrictions, (n-1)-fold splitting peaks appear at the low energies of conductance while (n-2)-fold splitting peaks appear at the high energies. The former resonant peaks are induced by the quasibound states mainly localized in the stubs, while the latter peaks are originated from the high quasibound states mainly localized in the constrictions. To the high quasibound states, the stubs act as potential barriers rather than wells. More quasibound states will exist in the constriction between two stubs, as the length of the constriction increases. For the periodic antidots arrays, (n-2)-fold splitting rule is also found around the first threshold energy.Based on chapter five, transmission resonant via quantum bound states in two typical periodic structures under magnetic field is studied in chapter six. For the electric superlattice consisting of n barriers, (n-1)-fold resonant peaks are shown in the beginning of the first conductance step under magnetic modulation. The peaks are induced by the magnetically quasibound states which wavefunctions are confined in the potential barriers rather than in the wells. For the open periodic multi-waveguides consisting of n constrictions, under magnetic modulation, the (n-2)-fold resonant splitting at the higher-energy region will change into (n-1)-fold splitting.In chapter seven, we study the conductance and local density of states of four kinds of L graphene nanoribbon. It is found that, the conductance around the Fermi-surface is determined by the type of graphene nanoribbon with armchair edge. As the nanoribbon is narrow, the conductance and density of states are very sensitive to the geometry of the structure.The last chapter presents a conclusion of this thesis and some prospects for this investigation.