Spin-Hall Effect And Related Transport Property In Two-dimensional Spin-orbit Coupling System

In this dissertation we have made a detail investigation on spin Hall effect and related transport property in two-dimensional spin-orbital interaction electron system. Here the discussed spin Hall effect is in the regime of the intrinsic one which is induced by the spin-orbital interaction relied on the structure of the system rather than on the impurity scattering.In chapter one we review the recent theoretical and experimental research on the spin Hall effect and bulk spin polarization in spin-orbital coupling systems. We discuss the origin of the spin-orbital interaction in atom with both the phenomenological analysis and the rigorous Dirac equation, and describe the spin-orbital coupling in solid, especially, the Rashba coupling in chapter two. And finally we give the eigen energies and eigen states for Rashba system. In chapter three the definition of the spin current and some related problem are discussed. By using the conventional definition, we first calculate the spin-Hall conductivity without impurity, and then consider the system in the diffusive regime.We discuss the properties of the linear Rashba system in the presence of the THz optical field in chapter four. For high frequency situation the clean assumption is valid, we discuss the system without impurity. We find that the spin-Hall current oscillates with the frequency of the THz field and its amplitude is influenced by the optical intensity. We observe the nonlinearity between the spin-Hall current amplitude and the optical intensity, amplitude may reach a maximum and then decrease. These feature may provide a different way to control the spin polarization and the spintronic devices optically in nonmagnetic semiconductors. Since the oscillated spin current is directly related to the bulk spin polarization, this provides a direct method to study the relationship between the traditional spin current density and the experimental measurement. Since the precise cancellation of spin-Hall conductivity in the Rashba model of two dimensional electron systems occurs only for the parabolic energy spectrum, in chapter five we consider the nonparabolic situation. For nonparabolic Kane dispersion, we find that the cancellation effect from the spin-dependent part of the ladder current vertex in the Born approximation for impurity scattering will not occur. The total spin Hall conductivity is finite and its value not only relates to the nonparabolic degree of the electron energy dispersion but also strongly depends on the smoothness of the disorder, and it increases with the increasing electron density. The overshoot phenomena analogous with the one of charge current is observed for the transient situation.In chapter six, we discuss other properties of this Rashba system by the balance equation approach. In the case of realistic impurity and phonon scatterings, the longitudinal conductivity is shown to depend on the spin-orbital coupling strength, though the transverse conductivity remains zero. The nonlinear effect of spin-orbital coupling on the y component of the spin polarization is observed, while the other components still vanish. At high temperatures, the phonon scattering has an impact on the suppression of the mobility peak and the spin polarization. In the nonlinear case, we find that the spin-orbital coupling may enhance the electron cooling, a clear saturation of spin polarization appears at high electric field, and the maximum y component of spin polarization the system can reach is limited by the spin-split strength. These features are in qualitative agreement with experimental results. We have also studied the effect of nonparabolicity due to Rashba coupling and find that it plays an appreciable role for low density and strong spin-orbital coupling system.The last chapter gives the conclusion and outlook of this dissertation.