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| 2. |
- Moskalenko, S. A., et al.
(författare)
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Coherence of two-dimensional electron-hole systems : Spontaneous breaking of continuous symmetries: A review
- 2013
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Ingår i: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 55:8, s. 1563-1595
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Forskningsöversikt (refereegranskat)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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| 3. |
- Moskalenko, S. A., et al.
(författare)
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Spontaneous Symmetry Breaking and Coherence in Two-Dimensional Electron-Hole and Exciton Systems
- 2012
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Ingår i: Journal of Nanoelectronics and Optoelectronics. - : American Scientific Publishers. - 1555-130X .- 1555-1318. ; 7:7, s. 640-670
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Forskningsöversikt (refereegranskat)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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| 4. |
- Moskalenko, S. A., et al.
(författare)
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Two-Dimensional Electron-Hole System under the Influence of the Chern-Simons Gauge Field Created by the Quantum Point Vortices
- 2021
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Ingår i: Semiconductors (Woodbury, N.Y.). - : Pleiades Publishing Ltd. - 1063-7826 .- 1090-6479. ; 55:SUPPL 1, s. S35-S48
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Tidskriftsartikel (refereegranskat)abstract
- The Chern-Simons (CS) gauge field theory was widely used to explain and to deeper understand the fractional quantum Hall effects. In this work, we apply the Chern-Simons gauge field theory to a two-dimensional (2D) electron-hole (e-h) system in a strong perpendicular magnetic field under the influence of the quantum point vortices creating by the Chern-Simons (CS) gauge field. The composite electron-hole particles with equal integer positive numbers phi of the attached quantum point vortices are described by the dressed field operators that obey to either the Fermi or Bose statistics depending on the even or odd numbers phi. It is shown that the phase operators, as well as the vector and scalar potentials of the CS gauge field, depend on the difference between the electron and the hole density operators. They vanish in the mean field approximation, when the average values of the electron and of the hole densities coincide. Nevertheless, even in this case, quantum fluctuations of the CS gauge field lead to new properties of the 2D e-h system. It is found that the numbers of vortices attached to each electron and hole are the same. This result is not obvious, and a different distribution of vortices in the environment of electron-hole pairs could be expected. A simple analytical formula is obtained for the shift of the magnetoexciton energy level at the point k = 0 due to the influence of the CS gauge field.
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| 7. |
- Clark, C. J., et al.
(författare)
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Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar
- 2018
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Ingår i: Science Advances. - : American Association for the Advancement of Science. - 2375-2548. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appear to pulsate as their emission beams cross our line of sight. To date,radio pulsations have been detected from all rotation-powered MSPs. In an attempt to discover radio-quiet gamma-ray MSPs,we used the aggregated power from the computers of tens of thousands of volunteers participating in the Einstein@Home distributed computing project to search for pulsations from unidentified gamma-ray sources in Fermi Large Area Telescope data. This survey discovered two isolated MSPs,one of which is the only known rotation-powered MSP to remain undetected in radio observations. These gamma-ray MSPs were discovered in completely blind searches without prior constraints from other observations,raising hopes for detecting MSPs from a predicted Galactic bulge population.
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| 8. |
- Dumanov, E. V., et al.
(författare)
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Interaction of two-dimensional magnetoexcitons
- 2017
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - : Elsevier BV. - 1386-9477 .- 1873-1759. ; 88, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- We study interaction of the two-dimensional magnetoexcitons with in-plane wave vector (k) over right arrow (parallel to) = 0, taking into account the influence of the excited Landau levels (ELLS) and of the external electric field perpendicular to the surface of the quantum well and parallel to the external magnetic field., It is shown that the account of the ELLS gives rise to the repulsion between the spinless magnetoexcitons with (k) over right arrow (parallel to) = 0 in the Fock approximation, with the interaction constant g decreasing inverse proportional to the magnetic field strength B (g(0) similar to 1/B). In the presence of the perpendicular electric field the Rashba spin-orbit coupling (RSOC), Zeeman splitting (ZS) and nonparabolicity of the heavy-hole dispersion law affect the Landau quantization of the electrons and holes. They move along the new cyclotron orbits, change their Coulomb interactions and cause the interaction between 21) magnetoexcitons with (k) over right arrow (parallel to) = 0. The changes of the Coulomb interactions caused by the electrons and by the holes moving with new cyclotron orbits are characterized by some coefficients, which in the absence of the electric field turn to be unity. The differences between these coefficients of the electron-hole pairs forming the magnetoexcitons determine their affinities to the interactions. The interactions between the homogeneous, semihomogeneous and heterogeneous magnetoexcitons forming the symmetric states with the same signs of their affinities are attractive whereas in the case of different sign affinities are repulsive. In the heterogeneous asymmetric states the interactions have opposite signs in comparison with the symmetric states. In all these cases the interaction constant g have the dependence g(0) - 1/root B.
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| 9. |
- Dumanov, E. V., et al.
(författare)
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Mixed exciton-plasmon collective elementary excitations of the Bose-Einstein condensed two-dimensional magnetoexcitons with motional dipole moments
- 2013
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 250:1, s. 115-127
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Tidskriftsartikel (refereegranskat)abstract
- The collective elementary excitations of the two-dimensional (2D) magnetoexcitons in the state of their BoseEinstein condensation (BEC) with nonzero wave vector k and inplane parallel oriented motional dipole moments are investigated in the HartreeFockBogoliubov approximation (HFBA). The breaking of the gauge symmetry is achieved using the Bogoliubov theory of quasiaverages and the KeldyshKozlovKopaev (KKK) method. The starting Hamiltonian and the Green's functions are determined using the integral two-particle operators instead of the single-particle Fermi operators. The infinite chains of equations of motion for the multioperator four- and six-particle Green-s functions are truncated following the Zubarev method and introducing a small parameter of the perturbation theory related with the lowest Landau levels (LLLs) filling factor and with the phase-space filling factor. The energy spectrum of the collective elementary excitations consists of the mixed excitonplasmon energy braches, mixed excitonplasmon quasienergy branches as well as the optical and acoustical plasmon energy branches. The exciton branches of the spectrum have gaps related with the negative values of the chemical potential and attractive interaction between the 2D megnetoexcitons with inplane, parallel oriented motional dipole moments. The slopes of the mixed excitonplasmon branches are determined by the group velocities of the moving condensed excitons in the laboratory reference frame. The acoustical and optical plasmon energy branches are gapless. Their dependence on the small wave vectors accounted from the condensate wave vector k is linear and quadratic, respectively, with saturation in the range of high values of the wave vectors.
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| 10. |
- Hakioglu, T., et al.
(författare)
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The influence of the Rashba spin-orbit coupling on the two-dimensional magnetoexcitons
- 2011
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23:34, s. 345405-
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field.
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