Spin-polarized nano-systems theory and transport properties

　　Title: Spin-polarized nano-systems theory and transport properties of
　　Author: Li important
　　Degree-granting units: Fudan University
　　Keywords: Spintronics;; spin - orbit coupling;; spin Hall effect;; molecular electronics;; density functional theory;; spin polarization;; evanescent waves;; local state;; single-layer graphite;; carbon atom chain;; spin transport
　　Abstract:
　　Spintronics major research role of the spin of electrons in solids as well as effective control of the electron spin and the operation is a combination http://www.chinamagnets.biz/ of magnetic and cross-disciplinary and microelectronics. As the use of electron spin have been developed in line with the nature of industrial development needs, spintronics in recent years become a very popular field of study. Spin - orbit coupling effect is the field of spintronics is an important research branch. Spin - orbit coupling to the electron orbital motion and spin of electrons linked together, providing people with an external electric field may be used to control the movement of electrons, and thus the means to control electron spin. Such an all-electrical, no external magnetic field or magnetic materials can control the spin of the method has aroused wide interest and enthusiasm for research. By spin - orbit coupling caused by the discovery of the spin Hall effect is to promote awareness of the spin - orbit coupling effect and spintronics research. Another has the potential to revolutionize today's electronics industry development area of ​​research is molecular electronics, it is trying to bottom, from atoms, molecules start to build a new generation of electronic devices. With the scanning tunneling microscope, self-assembly, split end technology, the development of experimental techniques and first principles density functional theory calculations and other advances in research methods, molecular electronics has also been rapid development in recent years. Experimentally and theoretically, it is through electric, magnetic, force, optical, chemical, electrochemical and other effects to control electronic transport in molecular junctions course, to expect to achieve at the molecular scale electronic devices function. In spintronics and molecular electronics-related fields, this Rare earth magnets theory of nano system of spin - orbit coupling, spin polarization and spin transport properties and other characteristics.
　　The first chapter briefly describes the spintronics and molecular electronics much attention to these two research areas. Spintronics associated with the spin - orbit coupling and spin Hall effect were also introduced.
　　The second chapter describes some of the theories used in this article research methods, including: flat and the model wave expansion method, density functional theory and nonequilibrium Green function method.
　　Chapter III analyzes the Rashba spin - orbit coupling caused by spin polarization. Equilibrium, due to time reversal invariance, the spin - orbit coupling does not cause any spin polarization. In the steady state value, due to system geometry and symmetry of the Hamiltonian, spin-polarized distribution of certain symmetry. We focus on the Rashba ballistic system in the steady state value, the decay of its spin-wave polarization effects. Consideration of wave attenuation will help to improve the numerical accuracy and reliability to ensure the linear response approximation system to be the "about" symmetry. Although the local area in the vicinity of the interface wave attenuation due to wave and plane wave attenuation of the coupling, its effect on the spin polarization also has a long-term nature. Wave attenuation effects of spin-polarized electrons with the incident energy has a very close relationship. Finally, we also discussed the wave attenuation effects of the spin current.
　　Chapter IV studies the extension of state and local state of polarization of the spin Hall effect. Although the pure spin Hall polarization of the evanescent wave contribution is almost negligible, but the extension of local states and mixed states on spin Hall polarization term has a great impact. In the Rashba narrowband system, the mixed term effects on spin Hall polarization dominant; in the wider system, the extension is based on the contribution of state-based. As the competition between the two, with the system width or Rashba coupling strength changes, the spin Hall polarization flip will occur. The width of the spin flip and system characteristics have a close relationship Rashba length. In the semi-infinite system, with the Rashba coupling strength changes, this spin-flip phenomenon does not exist.
　　Chapter V briefly describes the single-layer graphene, monolayer graphene and then studied in Ni (111), Au (111) and Ag (111) metal substrates on the spin - orbit coupling effect. Placed on Ni (111) graphite substrate on the existence of a single spin - orbit coupling effect; However, the single-band Rashba splitting graphite only about the size of 10 meV. This spin - orbit coupling effects from the metal substrate in a single layer of graphite near the interface with the interaction. In the single-layer graphite / Au (111) the stability of the system, single-layer graphite band spin - orbit coupling splitting about 25 meV can be achieved. We did not find single-layer graphene spin - orbit coupling and electron transfer system has a direct relationship between the local electric field near the interface of the model is not suitable to explain this effect.
　　Chapter VI using first-principles calculations of the single-layer graphene can be carved through the cut made of carbon atoms in its chain of magnetic spin-polarized transport properties. Isolated and short carbon chain may have very interesting magnetic characteristics. C2. Pure carbon atom chain with 2μB the total magnetic moment of the magnetic atoms are mainly distributed in the end of the chain. For nitrogen doped carbon chain NC2n +1 N and CnNCn, its magnetic ground state of the spin density wave with a similar distribution pattern. C2n +1 and NC2nN atomic chain is not magnetic. All of these magnetic characteristics of atomic chains of atoms can be in the chain through the bonding between atoms and how the system state and the unpaired electron is well explained. When the atomic chain placed between the non-magnetic metal electrodes to form a transport system, its magnetic properties will be greatly weakened. However, by some stretch effect, placed between two gold electrodes of the nitrogen-doped carbon chain can be an excellent spin filtering effect. For itself and does not have magnetic chain of carbon atoms, they have different Fermi spin-polarized conductivity characteristics. Even taking into account the spin polarization, the total conductance of the carbon atom chain of the parity oscillations still exist.
　　Chapter VII is a brief summary of this article.