The Theoretical Study On Electron And Spin Transport Properties In Quantum Dot System

As the typical representation exhibiting quantum effects, quantum dot system hasbecome one of the most active areas in mesoscopic physics in resent years. In this paper,using Green，s function approach, we investigate the electron and spin transportproperties in some typical quantum dots structure.First, we study the transport properties of a quantum dot embedded in one arm ofan AB ring, with a magnetic flux threading the ring. The numerical results show that thetwo conductance peaks show a typical Fano resonance shape due to the interference ofelectrons passing the two arms of the AB ring. The phase difference between the twopaths can be controlled by adjusting the magnetic flux. When there is a split level withinthe quantum dot, different spin electrons occupy different level. The resonance peak ofconductance for spin up and spin down electrons appear atE=-E_d-U,E EdandE=E_d-U，E=E_drespectively. At some levels, spin-polarization arrives at100%.Moreover, when the energy level is fixed, the conductance is a2-periodic functionswith respect to magnetic flux..Second, a quantum dot coupled to two electrodes with spin-dependent splitting ofchemical potentials (spin bias) is proposed as a detector of an individual electron spin.Spin polarized transport properties through the quantum dot have been investigatedtheoretically by means of the nonequilibrium Green’s function formalism. We found thatthe direction of current flow is dependence on the electronic spin state in quantum dot.Measuring the direction of the current flow through the devices, we can determine thedirection of the electronic spin state in quantum dot. This proposed detector provides apractical and all electrical approach to detect the electronic spin state in quantum dotstructure.Last, based on the nonequilibrium Green function method, quantum transportthrough a benzene-shaped quantum dots system is studied. It is shown that theconductance spectrum is sensitive to the arrangement of energy levels of dots. When theenergy levels of dots are mismatched, the conductance shows apparent asymmetricstructure and striking novel conductance dips appear due to the interference between two distinct paths. The differential conductance as a function of magnetic flux alwaysexhibits2π period. An overall suppression of differential conductance emerges for thecondition that the levels of dots are all aligned and=(2n+1)π(n is an integer). Inaddition, the influence of temperature on the differential conductance is presented.