| 1. |
- Moskalenko, S. A., et al.
(author)
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Coherence of two-dimensional electron-hole systems : Spontaneous breaking of continuous symmetries: A review
- 2013
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In: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 55:8, s. 1563-1595
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Research review (peer-reviewed)abstract
- The spontaneous breaking of the continuous symmetries of a two-dimensional electron-hole system in a strong magnetic field perpendicular to the plane leads to the formation of new ground states and determines the energy spectrum of collective elementary excitations that appear above these new ground states. In this review, the main attention is paid to the electron-hole system formed from coplanar magnetoexcitons under conditions of Bose-Einstein condensation in the ground state with the wave vector k = 0 taking into account the influence of excited Landau levels, when exciton-type elementary excitations coexist with plasmon-type oscillations. At the same time, the properties of a two-component system consisting of a two-dimensional electron gas and a two-dimensional hole gas spatially separated in a double quantum well under conditions of the fractional quantum Hall effect are of great interest, because these properties can affect the quantum states of magnetic excitons that are formed when the distance between the layers tends to zero. Bilayer electron systems are also considered under conditions of the fractional quantum Hall effect with the one-half filling factor for each layer and the total filling factor equal to unity for both layers. The coherence between the electron states in the two layers is equivalent to the formation of excitons in a macroscopic coherent state. This makes it possible to compare the energy spectrum of collective elementary excitations of Bose-Einstein condensed excitons under conditions of the quantum Hall effect and coplanar magnetoexcitons. The breaking of the global gauge symmetry or of the continuous rotational symmetry leads to the formation of a gapless spectrum of the Nambu-Goldstone type, whereas the breaking of the local gauge symmetry is accompanied by the appearance of a gap in the energy spectrum (Higgs phenomenon). These phenomena are equivalent to the formation of massless and massive particles in the relativistic physics. The application of the Nielsen-Chadha theorem, which determines the number of Nambu-Goldstone modes as a function of the number of broken symmetry operators, is demonstrated using the example of Bose-Einstein condensation of spinor atomic gases in an optical trap. This example is presented for a better understanding of the results obtained in the case of a Bose-Einstein condensation of coplanar magnetoexcitons. The Higgs phenomenon leads to the formation of composite particles under conditions of the fractional quantum Hall effect. Their description is given in terms of the Ginzburg-Landau theory. The possibilities for the appearance of spontaneous coherence in a system of indirect excitons in structures with a double quantum well are analyzed. The experimental attempts to create these conditions, the main results obtained in this field, and the accumulated knowledge are reviewed. The basic properties of the energy spectrum of magnetoexciton polaritons in a microcavity are formulated. A hypothesis is put forward about the possibility of forming two-dimensional magnetoexcitons and two-dimensional magnetoexciton polaritons of high density with attached point quantum vortices, i.e., about the possibility of forming new composite particles.
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| 2. |
- Moskalenko, S. A., et al.
(author)
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Spontaneous Symmetry Breaking and Coherence in Two-Dimensional Electron-Hole and Exciton Systems
- 2012
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In: Journal of Nanoelectronics and Optoelectronics. - : American Scientific Publishers. - 1555-130X .- 1555-1318. ; 7:7, s. 640-670
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Research review (peer-reviewed)abstract
- The spontaneous breaking of the continuous symmetries of the two-dimensional (2D) electron-hole systems in a strong perpendicular magnetic field leads to the formation of new ground states and determines the energy spectra of the collective elementary excitations appearing over these ground states. In this review the main attention is given to the electron-hole systems forming coplanar magnetoexcitons in the Bose-Einstein condensation (BEC) ground state with the wave vector (k) over right arrow = 0, taking into account the excited Landau levels, when the exciton-type elementary excitations coexist with the plasmon-type oscillations. At the same time properties of the two-dimensional electron gas (2DEG) spatially separated as in the case of double quantum wells (DQWs) from the 2D hole gas under conditions of the fractional quantum Hall effect (FQHE) are of great interest because they can influence the quantum states of the coplanar magnetoexcitons when the distance between the DQW layers diminishes. We also consider in this review the bilayer electron systems under conditions of the FQHE with the one half filling factor for each layer and with the total filling factor for two layers equal to unity because the coherence between the electron states in two layers is equivalent to the formation of the quantum Hall excitons (QHExs) in a coherent macroscopic state. This makes it possible to compare the energy spectrum of the collective elementary excitations of the Bose-Einstein condensed QHExs and coplanar magnetoexcitons. The breaking of the global gauge symmetry as well as of the continuous rotational symmetries leads to the formation of the gapless Nambu-Goldstone (NG) modes while the breaking of the local gauge symmetry gives rise to the Higgs phenomenon characterized by the gapped branches of the energy spectrum. These phenomena are equivalent to the emergence of massless and of massive particles, correspondingly, in the relativistic physics. The application of the Nielsen-Chadha theorem establishing the number of the NG modes depending of the number of the broken symmetry operators and the elucidation when the quasi-NG modes appear are demonstrated using as an example related with the BEC of spinor atoms in an optical trap. They have the final aim to better understand the results obtained in the case of the coplanar Bose-Einstein condensed nnagnetoexcitons. The Higgs phenomenon results in the emergence of the composite particles under the conditions of the FQHE. Their description in terms of the Ginzburg-Landau theory is remembered. The formation of the high density 2D magnetoexcitons and magnetoexciton-polaritons with point quantum vortices attached is suggested. The conditions in which the spontaneous coherence could appear in a system of indirect excitons in a double quantum well structures are discussed. The experimental attempts to achieve these conditions, the main results and the accumulated knowledge are reviewed.
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| 3. |
- Agekyan, V F, et al.
(author)
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Effect of a magnetic field on energy transfer of band states to the Mn2+ 3d shell in the CdMgTe matrix with ultrathin CdMnTe layers
- 2010
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In: PHYSICS OF THE SOLID STATE. - 1063-7834. ; 52:1, s. 27-31
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Journal article (peer-reviewed)abstract
- The effect of external magnetic fields on two radiative (band-to-band and on-site) recombination channels in II-VI dilute magnetic semiconductors and related nanostructures has been considered. The 3d on-site emission of manganese ions in CdMgTe matrices containing periodic inclusions of CdMnTe narrow-band-gap layers with thicknesses of 0.5, 1.5, and 3.0 monolayers has been investigated in magnetic fields of up to 6 T. It has been shown that, in a magnetic field, luminescence of manganese ions weakens because of the decrease in the rate of spin-dependent excitation transfer from band states to the Mn2+ 3d shell. The maximum suppression of 3d luminescence has been observed in the matrix with a CdMnTe layer 3.0 monolayers thick. This indicates that the main factor responsible for the energy transfer is the internal field near the CdMnTe layers, which determines the magnetic splitting and spin polarization of band states.
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| 4. |
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| 5. |
- Agekyan, V F, et al.
(author)
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Magnetoluminescence of CdTe/MnTe/CdMgTe heterostructures with ultrathin MnTe layers
- 2011
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In: Semiconductors (Woodbury, N.Y.). - : MAIK Nauka/Interperiodica (and#1052;and#1040;and#1048;and#1050; and#1053;and#1072;and#1091;and#1082;and#1072;/and#1048;and#1085;and#1090;and#1077;and#1088;and#1087;and#1077;and#1088;and#1080;and#1086;and#1076;and#1080;and#1082;and#1072;). - 1063-7826 .- 1090-6479. ; 45:10, s. 1301-1305
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Journal article (peer-reviewed)abstract
- CdTe/MnTe/CdMgTe quantum-well structures with one or two monolayers of MnTe inserted at CdTe/CdMgTe interfaces were fabricated. The spectra of the excitonic luminescence from CdTe quantum wells and their variation with temperature indicate that introduction of ultrathin MnTe layers improves the interface quality. The effect of a magnetic field in the Faraday configuration on the spectral position of the exciton-emission peaks indicates that frustration of magnetic moments in one-monolayer MnTe insertions is weaker than in two-monolayer insertions. The effect of a magnetic field on the exciton localization can be explained in terms of the exciton wave-function shrinkage and obstruction of the photoexcited charge-carrier motion in the quantum well.
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| 6. |
- Larsson, Arvid, et al.
(author)
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Magnetic field enabled charge state control of single InAs/GaAs quantum dots
- 2009
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In: 2009 9th IEEE Conference on Nanotechnology, IEEE NANO 2009. ; , s. 510-512
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Conference paper (peer-reviewed)abstract
- Micro-photoluminescence in the presence of an external magnetic field is employed to study individual InAs/GaAs quantum dots (QDs). By varying the strength of the applied magnetic field, the charge state of the QD is tuned from a double negatively charged exciton to a neutral exciton. This effect is shown to be related to carrier transport in the QD-plane prior to capture into the QD. The temperature dependence of the tuning effect is discussed. © 2009 IEEE NANO Organizers.
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| 7. |
- Larsson, L. A., et al.
(author)
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Quantum Dot Charging By Means Of Temperature And Magnetic Field
- 2011
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In: AIP Conference Proceedings. - : AIP. - 0094-243X.
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Conference paper (other academic/artistic)abstract
- A micro‐photoluminescence study of individual InAs/GaAs quantum dots is presented. It is demonstrated that by varying the strength of an applied magnetic field and/or the temperature, the charge state of a quantum dot can be tuned. The charge tuning mechanism is shown to be due to the modification of the electron and hole transport in the wetting layer plane prior to their capture into the quantum dot.
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| 8. |
- Larsson, L. A., et al.
(author)
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Spin Polarizing Neutral Excitons In Quantum Dots
- 2011
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In: AIP Conference Proceedings. - : AIP. - 0094-243X.
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Conference paper (other academic/artistic)abstract
- A high degree of spin polarization for the neutral exciton in individual InAs quantum dots, without any external magnetic field applied, is demonstrated. The polarization mechanism is shown to be due to the difference in capture time into the QD for the electrons and holes after photo excitation in the wetting layer. This leads to optical pumping of the QD nuclei by spin polarized electrons and hence suppression of the anisotropic electron—hole exchange interaction.
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| 9. |
- Larsson, L. Arvid, et al.
(author)
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Temperature and Magnetic Field Effects on the Transport Controlled Charge State of a Single Quantum Dot
- 2010
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In: NANOSCALE RESEARCH LETTERS. - : Springer Science Business Media. - 1931-7573 .- 1556-276X. ; 5:7, s. 1150-1155
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Journal article (peer-reviewed)abstract
- Individual InAs/GaAs quantum dots are studied by micro-photoluminescence. By varying the strength of an applied external magnetic field and/or the temperature, it is demonstrated that the charge state of a single quantum dot can be tuned. This tuning effect is shown to be related to the in-plane electron and hole transport, prior to capture into the quantum dot, since the photo-excited carriers are primarily generated in the barrier.
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| 10. |
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