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Title: Microcavity polaritons propagation, scattering, and localization
Author: Zajac, Joanna M.
ISNI:       0000 0004 2734 6458
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2012
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Strong coupling between a Fabry-Perot cavity mode and a quantum well exciton give rise to the new quasi-particles microcavity exciton-polaritons. Microcavity polaritons were for the first time demonstrated in 1992 in Ref [1] and since then, the field developed dramatically. Fundamental physics was explored in these systems including a quantum phase transitions of microcavity polaritons [2–4], demonstration of quantized vortices [5] and superfluidity [6]. Concerning applications [7], properties of microcavity polaritons are explored in optoelectronic devices e.g. low threshold electrically pumped polariton lasers, polarization sensitive optical bistable switches, spin memories and spin logic gates. Main research interest of this work concerned the field of quantum phase transitions and the many-body physics of microcavity polaritons which are relatively easily accessible experimentally as compared to similar physics in cold-atoms systems [8] from the point of view of equipment complexity. However, in polariton physics, samples with desirable properties play a crucial role. Microcavity samples commonly suffer from disorder, for both the exciton and the photon components of the polaritons, which strongly modifies polariton quantum effects and makes them difficult to interpret. This fact emphasizes the importance of the further development in the field of the sample design and growth, and this was one of the goals of this contribution. In particular, we worked to identify and suppress disorder in microcavity samples and to develop reproducible growth receipts providing samples with long photon lifetime. Photonic disorder was identified as cross-hatch dislocations and point-like-defects. A novel cross-hatch suppressing sample design was proposed and demonstrated, providing samples with long polariton propagation lengths in the order of millimeters in which genuine quantum fluid effects can be explored. Moreover, the origin behind the point-like-defects formation was identified as Ga nano-droplets deposited in microcavity during the molecular-beam epitaxial growth. These states were investigated using surface (differential-interference contrast microscopy, scanning-electron microscopy, chemical etching) and volume (focused-ion beam milling) techniques. Point-like-defect resulted in 0-dimensional polariton states exhibiting quantized energy levels which we have characterized in real and reciprocal space. The second part of this work was the investigation of quantum many-body effects in low disorder microcavities. In particular, we investigated polariton parametric scattering and demonstrated experimentally and theoretically scattering into ”ghost” branches which arises due to energy and momentum conservation of polaritons. Finally, we theoretically modeled quantum fluid effects of polaritons using Gross- Pitaievskii equation reproducing superfluid transition and bistability for spin independent polariton interactions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics