Tunneling Transport Of Electrons On The Surface Of A Topological Insulator Under The Modulation Of Spiral Magnetization Superlattices

Spintronics starting the discovery of giant magnetoresistance effect (GMR). It rapid development and has become a new branch of condensed-matter physics. It main research some novel phenomenon which are related to degrees of freedom of electronic spin, and utilize electronic spin to design new high-speed and low energy dissipation electronic devices. The operation of a spintronic device requires the generation, detection, and manipulation of the spin current. By means of the Spin-Orbit Coupling, we can control the spin by the electricity. Topological insulator is a new state of matter that was caused by the Spin-Orbit Coupling and its unique band structure.This material have a bulk band gap like an ordinary insulator, but have protected gapless edge state on their edge or surface. The 2D topological insulator is a quantum spin Hall insulator, which is a close cousin of the integer quantum Hall state. A 3D topological insulator supports novel spin polarized 2D Dirac fermions on its surface. These systems possess the characteristics of low power consumption and working in room temperature with no external magnetic field, being a significant steps for the further development of new semiconductor devices. In Chapter 1, we give a brief introduction to giant magnetoresistance (GMR), the development of spintronics and spin hall effect.In chapter 2, we investigate the transport properties of Dirac electrons on the surface of a 3D TIs attached with a spiral multiferroic oxide. Those Dirac electrons was modulated by the exchange interaction generated by the proximity of SMO. The orientation of the SMO magnetization is controlled by the spiral orderq. The tunability of the spiral wave vector q by gate voltages offers a way to modulate the conductance of the system. For the spiral plane of the SMO parallel to the spiral axis and the surface normal, the proximity-induced exchange field causes a particle-hole asymmetry and a transmission gap near the Dirac point. The transmission gap interval depends on the spiral wave vector q. This fact together with the tunability of q by gate voltages indicates an electric switch with high on-off ratios.