Quantum saturation and condensation of excitons in copper (I) oxide
Kavoulakis, Georgios
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https://hdl.handle.net/2142/23470
Description
Title
Quantum saturation and condensation of excitons in copper (I) oxide
Author(s)
Kavoulakis, Georgios
Issue Date
1996
Doctoral Committee Chair(s)
Baym, Gordon A.
Department of Study
Physics, Condensed Matter
Discipline
Physics, Condensed Matter
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
"Recent experiments on high-density excitons in Cu$\sb2$O provide evidence for degenerate quantum statistics and Bose-Einstein condensation of this nearly ideal gas. We model the time dependence of this bosonic system including exciton decay mechanisms, energy exchange with phonons, and interconversion between ortho (triplet-state) and para (singlet-state) excitons, using parameters for the excitonic decay, the coupling to acoustic and low-lying optical phonons, Auger recombination, and ortho-para interconversion derived from experiment. The single adjustable parameter in our model is the optical-phonon cooling rate for Auger and laser-produced hot excitons. We show that the orthoexcitons move along the phase boundary without crossing it (i.e., exhibit a ""quantum saturation""), as a consequence of the balance of entropy changes due to cooling of excitons by phonons and heating by the non-radiative Auger two-exciton recombination process. Our study implies that the Auger annihilation rate for para-para collisions is much smaller than that for ortho-para and ortho-ortho collisions due to the band structure of the material, explaining why, under the given experimental conditions, the paraexcitons condense while the orthoexcitons fail to do so. Furthermore, we review the band structure underlying the properties of excitons in Cu$\sb2$O and connect these properties to the Auger recombination process of excitons."
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