Andreev Conductance And Spin Current In Quantum Dots

Using nonequilibrium Green's function techniques,we have studied the transport properties of the spin-dependent electron in quantum dots.We first present the development of quantum dots,superconductor and ferromagnet,and then,introduce the nonequilibrim Green's function method.At last,we conclude our works in the past three years.We investigate Andreev reflection and Aharonov-Bohm oscillations through a parallel-coupled double quantum dots connected with a ferromagnetic lead and a superconductor lead.Andreev reflection and Aharonov-Bohm oscillations of the system is explored by tuning the interdot coupling,the gate voltage,the magnetic flux, and the intradot spin-flip scattering.Due to the asymmetrical levels of the two quantum dots,Fano resonant peaks occur.When the spin-flip scattering increases,Fano resonant peaks begin to split,and Aharonov-Bohm oscillations are suppressed.Due to the interdot coupling,one strongly and one weakly coupled states of the system can be formed.The magnetic flux can exchange the function of the two states,which leads to a swap effect.Spin current in the device with three normal metal leads via triple quantum dot in the presence of Rashba spin-orbit interaction and coulomb interaction were investigated.In the device,there is not magnetic field or magnetic material.Bying using nonequilibrium Green's function technique,we investigate spin current in normal metal.We find the spin current is affected by the strength of Rashba spin-orbit interaction and coulomb interaction.The oscillatory period of spin-up(spin-down) current is controlled by Rashba spin-orbit interaction.Increasing of bias voltage of leads producing spin current is always accompanied by the increasing of coulomb interaction.