Spin precession in spin-orbit fields under wire confinement and drift

This thesis reports on the effects of wire confinement and drift on the electron spin dynamics in gallium arsenide quantum wells. The spin dynamics in such systems is governed by spin-orbit interaction. The motivation for this work is explained in Chapter 1. Chapter 2 will provide the reader with background information on semiconductor quantum wells and what role spin-orbit interaction plays in such systems. It will particularly specify the relevant mechanisms that act on spins and introduce suffcient theoretical background for the reader to understand the results presented in the later chapters. The methodology is explained in Chapter 3. Scanning Kerr microscopy as the main experimental technique, as well as methods for data evaluation will be depicted. Chapter 4 focuses on the impact of wire confinement. Two studies are presented that evaluate measured spin dynamics for increasing wire confinement for two different symmetries of the spin-orbit interaction. The data is compared to theoretical models and we find that wire confinement affcts the spin dynamics differently in the two cases. While in one the impact is a suppression of diffusion, in the other it is an enhancement of the spin lifetime by an order of magnitude. The interplay between drift motion and diffusive motion is the subject of Chapter 5. It is demonstrated that, under drift, quasistationary electrons experience a temporal spin precession in the absence of an external magnetic field. The corresponding frequency scales linearly with the drift velocity. This unexpected finding is explained theoretically as a consequence of nonlinear terms of the spin-orbit interaction, for which drift leads to a spin precession angle twice that of spins that diffuse the same distance. In an outlook section, measurements are presented that show that under certain conditions a higher-order regime is accessible in which the spin precession depends nonlinearly on the drift velocity. Based on this nonlinear dependence, which is also predicted by a theoretical model, a novel scheme for spin amplification is developed in Chapter 6. The proposed concepts also profit from the findings of Chapter 4