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 Title: Bose-Einstein condensation of excitons in uniaxially stressed cuprous oxide Author(s): Lin, Jia Ling Department / Program: Physics Discipline: Physics Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Physics, Condensed Matter Abstract: Excitons in Cu$\sb2$O have been demonstrated to be a nearly ideal gas of bosons, providing a unique system for studying Bose-Einstein statistics and Bose-Einstein Condensation of an ideal gas in the laboratory. In this study, I have applied uniaxial stress to optimize the conditions for a Bose-Einstein Condensation phase transition of the excitons in this crystal. Using time-resolved photoluminescence, an enhanced quantum degeneracy of the orthoexcitons is observed in this stressed crystal due to the lowered multiplicity of the orthoexciton ground state, although no evidence of the condensation phase of the orthoexcitons is observed. In contrast, I have found compelling evidence for Bose-Einstein Condensation of the singlet paraexcitons in uniaxially stressed Cu$\sp2$O. When the paraexciton gas attains a particle density exceeding the critical density for Bose-Einstein condensation, the paraexciton spectrum develops an extra component at low energy which is about 0.1-0.3 meV above the zero-kinetic-energy state. I also observe an anomalous spatial transport of the paraexcitons when this low-energy component is present. This ballistic wave-like (or drift-like) motion occurs at an expansion rate 3 $\times$ 10$\sp5$ cm/sec to 4 $\times$ 10$\sp5$ cm/sec, roughly correlated with a blue-shift of 0.1-0.3 meV for the low-energy component of the paraexcitons. I therefore interpret the low-energy component of the paraexcitons as a Bose-Einstein condensation peak. Issue Date: 1994 Type: Text Language: English URI: http://hdl.handle.net/2142/20190 Rights Information: Copyright 1994 Lin, Jia Ling Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9522140 OCLC Identifier: (UMI)AAI9522140
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