Transport Properties Of Quantum Systems Driven By Spin Bias Voltage

Spintronics has been the main research field and has brought a major impact on the development of the microelectronics, optoelectronics and information industry. In this dissertation, we firstly reviews some of the effects of quantum transport, such as Quantum tunneling and Coulomb blockade effect, and introduces the spin bias voltage, pure spin current and none-equilibrium Green function approach. Next, the transport properties of quantum dots driven by spin bias in microwave field are studied. Numerical results show that the resonance peaks of spin current split and the pure spin current disappears due to the magnetic field destroying the degeneration of electron spin in quantum dot. When the time-dependent sine microwave field is imposed to the electrode, the quantum dot has more effective tunneling channels because electrons can absorb the photons. As a result, many side-peaks appear in the current curve. As the intensity of microwave field becomes stronger, the multiple-photon processes become more important. Finally, we study the transport properties of single molecular magnet driven by spin bias voltage. The single molecular magnet is simplified to a two energy-levels model if only considering two energy degenerate spin ground states with a macroscopic tunneling effect between them. The neutral state and the charged state of molecule are exchanged when the electron is through the molecule from one electrode to the other electrode. We utilize the Fock state of the molecule to constitute the Hamiltonian of model and calculate the spin-resolved current using non-equilibrium Green function technique. The pure spin current flows through the molecule under the spin bias voltage. With the increasing of transition energy of the molecule from the neutral state to the charged state which is controlled by gate voltage, different resonant energy levels pass through the spin bias window. When the resonant energy level is in the middle of the spin bias window, the peak of spin current appears. These conclusions contribute to a better understanding of quantum transport processes and provide a good basis to the development of spintronics.