Theoretical Study Of Quantum Transport Properties In The Superconductor/Normal Quantum Dot Composite System

Today,under the nanofabrication technology,we have been able to make complex mesoscopic structure of quantum dot molecule with superconducting electrodes in this experiment.It is not difficult to imagine,compared to the single quantum dot,quantum dot molecule with superconducting electrodes will have more abundant transport properties.On one hand,compared to the single quantum point,the system has various topologies and provides much more Feynman path for the electron transmission.When system scales is less than or close to the coherence length of the quasiparticle and superconductors,there will be rich quantum interference phenomenon in the system.On the other hand,because of the electronic exchange interaction between quantum-dot in molecules,another energy scale is the exchange coupling coefficient which is complex competitive with the Kondo temperature Tk and the superconducting energy gap of performance.Accordingly,0-? conversion phenomena of Josephson currents will appear new characteristic in this system.In this work,we have carried on the theoretical research for the structure of a superconductor/quantum dot molecule/superconductor Josephson current by means of exact diagonalization techniques,the results are as follows:Firstly,we have carried on the theoretical research for the structure of a S/TQD/S Josephson effect by means of exact diagonalization techniques.Study found that,when we consider the strong coulomb interaction in the quantum dots,the Josephson current in the system will be affected by the different correlation mechanism and show the complex phase transition results.Specifically speaking,we found that 0-? phase transition is due to the inter-dot antiferromagnetic and various kinds' correlations mechanism if the electron in the quantum dots is half-filled.By adjusting the related parameters of the structure,we observed rich Josephson phase transition by Kondo effect?spin correlation between quantum dots and Cooper correlations in the superconducting controlled.Secondly,we investigated the S/CQD/S Josephson effect.The interplay between the Kondo effect,spin correlation between quantum dots,and Cooper correlations in the superconductors can induce rich Josephson phase transition phenomena.More interestingly,the indirect spin correlation can be constructed significantly between the two lateral quantum dots in some energy regions of the system.The phenomenon will be good for quantum dots system to realize spin correlation of indirect control which is based on Josephson effect.