Spin Transport through One-Dimensional Systems with Periodic Structures

• Main Authors: Jhih-Sheng Wu, 吳致盛
• Other Authors: Ching-Ray Chang
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/41505131521159155246

碩士 === 國立臺灣大學 === 物理研究所 === 98 === The thesis presents a theoretical study of spin transport in one-dimensional systems with periodic structures. In this thesis, all the transport is in the ballistic regime and one-dimensional systems are made by confining electrons in two-dimensional systems. The main purpose of this thesis is to investigate the effects of spin-orbit coupling (SOC) and magnetic field on spin transport, especially spin filtering in one-dimensional systems with periodic structures. In solids, SOC describes the interaction between the momentum of an electron and its own spin. The symmetry breaking of space inversion of the solid structure gives rise to two kinds of SOC: (i) Rashba SOC and (ii) Dresselhaus SOC. Rashba SOC, originated from structure inversion asymmetry (SIA), can be tuned by voltage gates while Dresselhaus SOC, originated from bulk inversion asymmetry (BIA), can be not easily controlled. Two methods are used to create periodic SOC in space: (i) to modulate Rashba SOC periodically by voltage gates and (ii) making a periodically curved wire. The periodic SOC in space can make a band structure with spin-dependent band gaps. SOC contributes an effective magnetic field, which has time reversal symmetry. With the two methods, we can control the effective magnetic field. The influences of the absolute value and the direction of the effective magnetic field are studied. It have been shown that without breaking time reversal symmetry, single-channel one-dimensional systems can not have spin filtering properties. Therefore, the effect of an exterior magnetic filed applied to the one-dimensional systems is examined. This exterior magnetic filed moves the spin-dependent band gaps to different energy levels. When electrons'' energies lie in these spin-dependent band gaps, full spin-polarized current is produced. In chapter 1, the motivation is mentioned in the start and an introduction to electron transport in the ballistic regime and the origin of SOC is given . Chapter 2 will be devoted to confined quantum systems in curvilinear space. The curvilinear effects on kinetic energy and SOC are both described. In chapter 3, the methods for transmittance and band structures are introduced to investigate the properties of spin transport. The transmittance and band structures of specific systems are calculated in chapter 4. The effects of SOC, magnetic filed and geometric structures are discussed in the separate sections. Conclusion of the thesis will be summarized in chapter 5.