Proceedings of nanoGe September Meeting 2015 (NFM15)
Publication date: 8th June 2015
Charged quantum dots provide an important platform for a range of emerging quantum technologies from spin qubits to single phonon sources. Colloidal quantum dots in particular could offer unique advantages for such applications (eg. facile synthesis, manipulation and compatibility with a wide range of environments), especially if stable charged states can be harnessed in these materials. We use engineered CdSe nanocrystal core and shell structures to efficiently ionize at cryogenic temperatures, resulting in stable trion emission from single nanocrystals exhibiting single sharp zero-phonon lines and mono exponential decays [1]. Magneto-optical spectroscopy of single nanocrystals reveals Zeeman splitting of the single line into four spectral lines from which the Landé g-factors for both the electron and hole can be directly measured. Surprisingly, we find that spherical CdSe nanocrystals with a zinc-blende crystal structure have isotropic g-factors in analogy to atomic species. This presents an exciting new engineering direction towards orientation-free quantum dots. Furthermore, a pronouced onset of spin relaxation in the excited state shows up for Zeeman splittings approaching the energy of the lowest l=2 acoustic phonon mode. This is a signature of an acoustic phonon bottleneck effect, which is a phenomenon unique to colloidal nanocrystals, due to their finite size [1]. The presentation will also be dedicated to our spectroscopic investigations on the band-edge exciton fine structure [2-5], which provide a spectral fingerprint of the low energy sub-levels, revealing the morphology and the crystal structure of individual nanocrystals. In order to probe the entire band-edge exciton fine structure, a high resolution luminescence excitation technique has been developed. Zeeman and anisotropy-induced splittings are used to reveal the entire 8-state band-edge fine structure, enabling a complete comparison with band-edge exciton models. State-selective excitation enables the preparation of single quantum states. It is also used to map the hole spin relaxation pathways between the fine structure sublevels.
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