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Optically controlled carrier and Nuclear spintronics: towards nano-scale memory and imaging applications (OptoDNPcontrol)
Start date: Feb 1, 2013, End date: Jan 31, 2018 PROJECT  FINISHED 

Carrier spin states in semiconductor nano-structures can be manipulated with fast optical pulses via the optical selection rules. The electron and hole spins in quantum dots interact strongly with the nuclear spins in the host material via the hyperfine interaction. This allows a new, versatile approach to nuclear spintronics, namely applying fast optical initialisation to carrier states and subsequent transfer via dynamic nuclear polarisation (DNP) of the spin information onto long-lived nuclear spin states, with promising applications in quantum information science and novel nuclear magnetic resonance (NMR) techniques.This project aims to develop new, efficient optical pumping schemes to maximise DNP by going beyond the established Overhauser effects, investigating the possibility of self-polarization and phase transitions of the nuclear spin ensemble. An innovating aspect of this proposal is to use valence state engineering to tailor the highly anisotropic dipolar interaction between nuclei and holes, which can lead to novel, non-colinear hyperfine coupling.The next innovation proposed is the development of an all-optical technique AONMR that does not require any radiofrequency (rf) coil set-up capable to control mesoscopic spin ensembles. Contrary to standard NMR techniques based on the generation of macroscopic rf-fields, AONMR can address the nuclear spins in one single nano-object via resonant laser excitation.A further important target is to use quantum dots and other carrier localisation centres as efficient sources of DNP generation and to carry out a detailed study of the diffusion of DNP throughout the sample and finally across the sample surface, varying key sample (chemical composition, strain, substrate orientation) and experimental parameters such as temperature and applied external fields. These experiments are a feasibility study for using hyperpolarized compound semiconductors for increasing the sensitivity in Magnetic Resonance Imaging (MRI).
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