The Spin-polarized Transport In Semiconductor Quantum Structures

Electronic spin transport in semiconductor quantum structures are important issues in condensed matter physics and have attracted considerable attention in recent years. In this thesis we present some detailed theoretical investigations on electronic spin transport in semiconductor quantum structures.The effects of magnetic field and bias voltage on spin polarized electron transport through a dual magnetic barriers quantum structure are investigated in this paper. The results show that: (i) the spin-polarization of electron can not be produced in the anti-parallel magnetic barriers structure at zero bias voltage; (ii) the energy threshold of electronic transmission are increase with the increases of magnetic field or bias voltage; (iii) the comparison of the electron spin polarization degree is made between the electron transport through GaAs and through InAs quantum structure, and find that though the spin polarization degree oscillation decrease with the increase of the incidence energy, the spin polarization degree of InAs is an order of magnitude higher than that of GaAs because of the higher Lande effective factor.The infuence of Rashba spin-orbit coupling on the spin-polarized transport were investigated by effective-mass theory. At a critical value of the strength of the Rashba effect, the spin polarization of the current is resonantly enhanced, due to the special structure of the Landau levels. Our above work shows that spin-polarized current can be generated by energy band or energy level engineering in a weakly spin-polarized system. We investigates the electric-field-induced Rashba spin splitting in quantum wells using the eight-band effective-mass model. Through improved derivation we obtain an analytical expression for Rashba spin splitting. Results show that Rashba spin splitting is intrinsically a nonlinear function of the wave vector. We propose a two-parameter nonlinear Rashba model, which solves the disagreement between recent numerical results (showing that Rashba spin splitting exhibits certain nonlinear behaviors) and the widely used analytical model (i.e., the linear Rashba model, which treats Rashba spin splitting as a linear function of the wave vector).