Research On The Electronic Transport Properties In Carbon Nanotube Structures

As one of typical nanomaterials, carbon nanotube may has great potential applica-tions in the nanoelectronics and future quantum devices, due to their unique geometrystructures and physical properties. In this thesis,we study the electronic transportproperties in some carbon nanotube structures,and analyze the conductance and lo-cal electronic structures in these systems. The results are discussed and interpreted indetail.We deal with the junction between two parallel nanotubes within theπelectrontight-binding model. Coupling parameters are adopted to describe the nanotube junc-tion. It is found that conductance shows oscillating behavior with the increase of cou-pling strength and coupling length. We calculate the local densities of states in thejunction, and find that the conductance oscillation concur with the ?uctuation of lo-cal densities of states. We point out that the phenomena observed are origin from thescattering due to the local electronic structures in the junction.We study the Rashba spin-orbit coupling induced by adatoms in carbon nanotubes,starting from the analogy with the spin-orbit coupling in two dimensional electron gassystems. The effects of Rashba term on the electronic transport are investigated. It isfound spin-orbit coupling break the energy orbit generacy at the Fermi level. Whenthe coupling strength becomes strong enough, the conductance peak near the Fermilevel will get splitted. The spin-valve effect of carbon nanotube based magnetic tunnel-ing junction changes because of the appearance of spin-orbit coupling. The magneticresistance depends on the coupling strength between the carbon nanotube and the fer-romagnetic electrodes. It shows different behaviors according to the magnitude of thecontact coupling. The phenomena can be attributed to the spin-?ip process and the splitof conductance peak induced by spin-orbit coupling.We also study the Kondo effect induced by magnetic impurities on the electronictransport at finite temperature in carbon nanobutes by using Anderson model. The mag-netic impurities induce Kondo resonance near the Fermi level, and hence a conductancedip appears. As the temperature increases, the Kondo resonance peak and the conduc- tance dip fade out, and the total conductance increases. Based on the Mott relation, weinvestigate the thermoelectric power of carbon nanotubes with magnetic impurities. Itchanges the sign near the Fermi level due to the emergence of Kondo resonance. Atlow temperature, thermoelectric power increases with the increasing temperature, andthen it gets decrease after reaching a peak value. When scaled x axis according to theKondo temperature, we get the dependence of thermoelectric power on the absolutetemperature, and find that it can interpret the results in the experiments well.