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Influence of Coulomb scattering of electrons and holes between Landau levels on energy spectrum and collective properties of two-dimensional magnetoexcitons
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2007 (English)In: Physica. E, Low-Dimensional systems and nanostructures, ISSN 1386-9477, E-ISSN 1873-1759, Vol. 39, no 1, 137-149 p.Article in journal (Refereed) Published
Abstract [en]

This study is concerned with a two-dimensional electron-hole system in a strong perpendicular magnetic field with special attention devoted to the influence of the virtual quantum transitions of interacting particles between the Landau levels. It is shown that virtual quantum transitions of two Coulomb interacting particles from the lowest Landau levels to excited Landau levels with arbitrary quantum numbers n and m and their transition back to the lowest Landau levels in the second order of the perturbation theory result in indirect attraction between the particles supplementary to their Coulomb interaction. The influence of this indirect interaction on the chemical potential of the Bose-Einstein condensed magnetoexcitons and on the ground state energy of the metallic-type electron-hole liquid (EHL) is investigated in the Hartree-Fock approximation. The supplementary electron-electron and hole-hole interactions being averaged with direct pairing of operators increases the binding energy of magnetoexciton and the energy per pair in the EHL phase. The terms obtained in the exchange pairing of operators give rise to repulsion. Together with the Bogoliubov self-energy terms arising from the electron-hole supplementary interaction they both influence in the favor of BEC of magnetoexcitons with small momentum. The influence of the excited exciton bands on the energy spectrum and on the wave function of the lowest magnetoexciton band is studied in the second order of the perturbation theory. The BEC of magnetoexcitons in the superposition state is considered. The generalized Bogoliubov transformations, the BCS-type ground state wave function and the phase-space filling factors of the lowest and first excited Landau levels are determined.

Place, publisher, year, edition, pages
2007. Vol. 39, no 1, 137-149 p.
Keyword [en]
Bose-Einstein condensation, Magnetoexcitons
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-94783DOI: 10.1016/j.physe.2007.02.004ISI: 000248438000025OAI: oai:DiVA.org:uu-94783DiVA: diva2:168762
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2011-01-26Bibliographically 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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