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Collective elementary excitations of Bose-Einstein condensed two-dimensional magnetoexcitons strongly interacting with electron-hole plasma
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
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2005 In: Moldavian Journal of the Physical Sciences, ISSN 1810-648X, Vol. 4, no 2, 55- p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2005. Vol. 4, no 2, 55- p.
URN: urn:nbn:se:uu:diva-94782OAI: oai:DiVA.org:uu-94782DiVA: diva2:168761
Available from: 2006-09-07 Created: 2006-09-07Bibliographically approved
In thesis
1. Bose-Einstein Condensation of Magnetic Excitons in Semiconductor Quantum Wells
Open this publication in new window or tab >>Bose-Einstein Condensation of Magnetic Excitons in Semiconductor Quantum Wells
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis regimes of quantum degeneracy of electrons and holes in semiconductor quantum wells in a strong magnetic field are studied theoretically. The coherent pairing of electrons and holes results in the formation of Bose-Einstein condensate of magnetic excitons in a single-particle state with wave vector K. We show that correlation effects due to coherent excitations drastically change the properties of excitonic gas, making possible the formation of a novel metastable state of dielectric liquid phase with positive compressibility consisting of condensed magnetoexcitons with finite momentum. On the other hand, virtual transitions to excited Landau levels cause a repulsive interaction between excitons with zero momentum, and the ground state of the system in this case is a Bose condensed gas of weakly repulsive excitons. We introduce explicitly the damping rate of the exciton level and show that three different phases can be realized in a single quantum well depending on the exciton density: excitonic dielectric liquid surrounded by weakly interacting gas of condensed excitons versus metallic electron-hole liquid. In the double quantum well system the phase transition from the excitonic dielectric liquid phase to the crystalline state of electrons and holes is predicted with the increase of the interwell separation and damping rate.

We used a framework of Green's function to investigate the collective elementary excitations of the system in the presence of Bose-Einstein condensate, introducing "anomalous" two-particle Green's functions and symmetry breaking terms into the Hamiltonian. The analytical solution of secular equation was obtained in the Hartree-Fock approximation and energy spectra were calculated. The Coulomb interactions in the system results in a multiple-branch structure of the collective excitations energy spectrum. Systematic classification of the branches is proposed, and the condition of the stability of the condensed excitonic phase is discussed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 67 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 211
Physics, Bose-Einstein condensation, magnetic excitons, electron-hole pairs, electron-hole liquid, magnetorotons, magnetoplasmons, superfluidity, Fysik
urn:nbn:se:uu:diva-7112 (URN)91-554-6636-2 (ISBN)
Public defence
2006-09-28, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Available from: 2006-09-07 Created: 2006-09-07Bibliographically approved

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