Transport in nanostructures with spin orbit interaction.

Abstract

Spin-orbit interactions (SOI) play important roles in the emerging field of spintronics by providing means to manipulate spins without the use of magnetic fields. In this thesis, we study the charge and currents flowing inside, and through, one-dimensional (1D), two-dimensional (2D) and quasi-one dimensional (Q1D) SOI systems. Understanding the transport characteristics of SOI systems is important in optimizing the performances of spin polarization and manipulation devices.

We first derive analytic formulae for the transmission and transmission coefficients in 1D interfaces between two RSOI segments with different RSOI strengths. We next present numerical results for these coefficients across 2D interfaces for spin polarized currents. We then present numerical results for how transport in a single 2D RSOI segment of finite width sandwiched between two non-RSOI leads varies with energy, incidence angle, RSOI segment length, RSOI strength and external potential for a spin polarized current. We use the results as a basis for understanding the transport properties when the incident current is spin unpolarized. We then calculate the transverse pure spin currents and the longitudinal spin polarization for systems consisting of both single and double-RSOI segments sandwiched between non-RSOI leads.

We next calculate the dispersion relations and eigenstates for Q1D RSOI systems, and give a short introduction to the Non-Equilibrium Green's Function (NEGF) formalism that will be used to calculate the transport properties in Q1D RSOI systems. We derive the key formulae used, and present results for the variation of the charge current with energy, RSOI segment length and RSOI strength, as well as the spin and charge accumulation and current distributions inside the RSOI segment. We present results for both polarized and unpolarized source currents. The spin current distribution in the RSOI segments for unpolarized currents motivate the subsequent consideration and analysis of RSOI segments with an off-centre defect and RSOI segments with two drain terminals for generating spin polarized drain currents from unpolarized source currents.

Finally, we present a multi-scale scheme that combines the NEGF scheme for the modelling of the SOI region and the Spin Drift Diffusion (SDD) model for modelling the diffusive transport that occur inside mesoscopic sized leads. We use this scheme to study the effects of a Dresselhaus SOI on spin injection from a ferromagnetic lead into a semiconductor lead through the SOI region.