THE EFFECT OF MILLITESLA MAGNETIC FIELDS ON ELECTRON-NUCLEAR SPIN DYNAMICS IN InGaAs QUANTUM DOTS

We present a comprehensive investigation of the electron-nuclear system of negatively charged InGaAs/GaAs self-assembled quantum dots under the influence of weak external magnetic fields (up to 2~mT). We demonstrate that, in contrast to conventional semiconductor systems, these small fields have a profound influence on the electron spin dynamics, via the hyperfine interaction. Quantum dots, with their comparatively limited number of nuclei, present electron-nuclear behavior that is unique to low-dimensional systems. We show that the conventional Hanle effect used to measure electron spin relaxation times, for example, cannot be used in these systems when the life times are long. An individual nucleus in the QD is subject to millitesla effective fields, arising from the interaction with its nearest-neighbors and with the electronic Knigh) field. The alignment of each nucleus is influenced by application of external fields of the same magnitude. A polarized nuclear system, which may have an effective field strength of several Tesla, may easily be influenced by these millitesla fields. This in turn has a dramatic effect on the electron spin dynamics, and we use this technique to gain a measure of both the dipole-dipole field and the maximum Knight field in our system, thus allowing us to estimate the maximum Overhauser field that may be generated at zero external magnetic field. One may fine-tune the angle which the Overhauser field makes with the optical axis.