Thermoelectric Transport In Quasi-One-Dimensional Defected Nanostructures

Based on non-equilibrium Green’s function method and linear response theory, we have investigated the electronic and spintronic transport in both quasi-one-dimentional (QID) nanowires with long-range correlated disorders and graphene nanoribbons with periodic defects. It is shown that the defects in Q1D nanostructures can effectively modulated the electronic and spintronic transport properties by electron-electron interaction and spin-orbit coupling. The main points of my dissertation are listed as follows:1. The normalized localization length of QID nanowires with long-range correlated disorders (LRCDs) as a function of energy and correlation exponent is investigated numerically by using generalized scattering matrix technique. It is found that both localization and delocalization are enhanced by LRCDs, similar to that observed in the microwave waveguide. Especially, the delocalization behavior can be controlled by adjusting the ratio of the ordered building blocks to disordered ones.2. The normalized localization length of two-side rough nanowires as functions of energy, magnetic field and correlation strength is numerically investigated by using modular recursive Green’s function method. It is found that in the absence of correlation, while in the presence of magnetic field, the localization length increases linearly for two-side roughness, which is different from diverging exponentially for one-side roughness. Moreover, the localization of electrons is suppressed in the low energy region, but enhanced in the high energy region. In the presence of correlation, an exponential enhancement in the localization length resumes in high energy region, in contrast to that in low energy region, the long-range correlations abnormally enhance the localization of electrons.3. The up-spin and down-spin normalized localization length of one-side rough nanowires with spin-orbit coupling is calculated numerically by using modular recursive Green’s function method. A semi-metal-insulator transition is observed. It is shown that the polarization is enhanced by increasing magnetic field, disorder degree and Lande factor, but reduced by increasing energy, correlation strength and Rashba strength.4. The thermoelectric properties of armchair graphene nanoribbons (AGNRs) with defects and magnetic field are investigated numerically by using non-equilibrium Green’s function method. For perfect armchair graphene nanoribbons, it is shown that with its width increasing, the maximum of the figure of merit ZT is monotonously decreased while the phononic thermal conductance increases linearly. In the presence of defects, the phononic thermal conductance decreases monotonously with the defect number increasing. Interestingly, the maximum of ZT values is proportional to the defect number in longitudinal direction, but inversely proportional to that in transversal direction. In the presence of magnetic field, very remarkable enhancement of ZT value is further obtained at the bottom of conduction band.5. The electronic properties and spin polarization of graphene nanoribbons (GNRs) with periodic defects are studied numerically by using non-equilibrium Green’s function method. The band splitting and spin-polarized edge states are observed, which results from electron-electron interaction. It is found that with the defects’ number increasing, the local magnetic moment increases and bandgap decreases.