Fano-Kondo Effect In Quantum Dots System Coupled To Ferromagnetic Leads

The Kondo effect was widely studied in condensed matter physics,it is a well-known physics phenomenon. The effect arises from the interactions between a single magnetic impurity and the electrons of the bulk mental under low temperature.Recent advances in nanofabrication technology have made it possible to investigate various aspects of this effect. One used Quantum Dots coupled to circuit by tunneling barriers under controlled circumstances experimentally, which has aroused new interest in this phenomenon. In contrast to the enhancement of the resistivity 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. Recently, a great effort has been dedicated to the study of Kondo effect in quantum dot coupled to ferromagnetic leads. In this thesis, we use the Keldysh nonequilibrium Green function and equation of motion technique to solve the Green function. We investigate the Fano-Kondo effect in a T shaped quantum dots coupled to ferromagnetic leads. On this basis, we have presented a qualitative study of spin-dependent transport of a triple-QD system in the Kondo regime. We have found that: (â…°) for antiparallel spin alignment the Kondo resonances for spin up and spin down configurations appear at the same position. (â…±) For parallel spin alignment, the Kondo resonance splits for spin up and spin down configurations. The down-spin resonance is enhanced and shift towards higher energy. However the up-spin resonance is suppressed and shift towards lower energy.. (â…²) Due to the existence of the coupled dots, the Kondo resonance and Fano interference coexist. Compared to the T-shaped QDs, the triple quantum dots system shows more variety of dip behaviors. The interdot coupling, the energy level of the side coupled QDs and the spin polarization strength greatly influence the DOS of the central quantum dot QD0. Either the increasing of the coupling strength between the two QDs or that of the energy levels of the side coupled QDs enhances the Kondo resonance. Especially, the Kondo resonance is strengthened greatly when the side dot energy is tuned at the Fermi energy. These novel results are helpful in exploring the electronic correlation in spintronics.