Kondo Effect In Ring- Dot Coupled To Ferromagnetic Leads

As the typical representation of exhibiting quantum effect in low dimensional mesoscopic system, the Kondo phenomenon quantum in dot system becomes the hot topic in condensed matter physics. In recent years, finding the clear Kondo phenomenon in tunnelling conductance of quantum dot, peple used Quantum Dots coupled tocircuit by tunneling barriers under controlled circumstances exprimentally. In contrast to the enhancement of heresistivity of the Kondo effect in a bulk metal, the Kondo resonance near the Fermi level localized at the quantum dot provides a new channel for the mesoscopic current and leads to an increase of the conductance in a quantum dot. In order to the study of Kondo effect in quantum dot coupled to ferromagnetic leads, we use the slave-boson mean-filed approximation and equation of motion technique to solve the Green function, for investigating the Kondo effect in a quantum dot coupled to ferromagnetic leads and a mesoscopic ring. The thesis shows that:(i) for anti-parallel spin alignment, the Kondo resonances of spin up and spin down configurations do not appear at the same position. And this agreement does not present periodic change by the aggrandizement of the magnetic flux, the intensity of polarization in ferromagnetic leads and the angle. (ⅱ) For parallel spin alignment, the Kondo resonance splits obviously for spin up and spin down configurations. At the same time, the Kondo resonance at the Fermi level of the dot presents the periodic-changing along with the aggrandizement of the magnetic flux and the number of lattice sites NR in the mesoscopic ring. (ⅲ) Both the Kondo resonance and the spin-splitting of the single electron levels can be controlled by internal magnetization of the electrodes, which can be used to generate a spin-valve effect. We can clearly certificate that this spin-valve effect was produced by strong correlation and coupled ferromagnetic leads, by the mesoscopic nature of the Kondo scattering.