Thesis defense of Eiko Evers

The nuclear spins in semiconductors can serve as a quantum mechanical system with minutes long spin relaxation times, enhanced by the decoupling from the surrounding matter in strained nanostructures and the absence of interaction with light. In order to manipulate the nuclear spin system optically, resident electrons confined in the nanostructure are introduced as a mediator. The electron localization leads to an efficient coupling of the electron spin to the nuclear spins via Fermi contact hyperfine interaction. This allows one to polarize the nuclear spins and to detect their dynamics. In this work, the nuclear spin dynamics in a cadmium telluride (CdTe) quantum well is characterized, assisted by nuclear magnetic resonance radio frequency pulses. The independent dynamics of the isotope spins turns out to be harmonized. In the enhanced localization in negatively doped indium gallium arsenide (InGaAs) quantum dots, two nuclear spin polarization protocols are assessed. Firstly, the developed extended pump-probe setup allows to investigate the established nuclei-induced frequency focusing by tracing the electron spin precession with improved spectral resolution. Secondly, a novel technique based on the pulsed excitation with 1 GHz pulse repetition frequency is introduced which allows to establish a substantial nuclear spin polarization in a transverse field while also reducing the fluctuations of the unordered nuclear spins.

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