| 170991. |
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| 170992. |
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| 170993. |
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| 170994. |
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| 170995. |
- 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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| 170996. |
- Moskalenko, S. A., et al.
(författare)
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Collective Elementary Excitations of Two-Dimensional Magnetoexcitons in the Bose-Einstein Condensation State
- 2009
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Ingår i: Journal of Nanoelectronics and Optoelectronics. - : American Scientific Publishers. - 1555-130X .- 1555-1318. ; 4:1, s. 52-75
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Forskningsöversikt (refereegranskat)abstract
- The collective elementary excitations of a system of two-dimensional magnetoexcitons in a state of Bose-Einstein condensation (BEC) with arbitrary wave vector was investigated in Hartree-Fock-Bogoliubov approximation. The breaking of the gauge symmetry of the Hamiltonian was introduced following the idea proposed by Bogoliubov in his theory of quasi-averages. The equations of motion were written in the frame of the starting electron and hole creation and annihilation operators. The chains of equations of motion for a set of Green's functions describing the exciton-type excitations as well as the plasmon-type excitations were deduced. Their disconnections were introduced using the perturbation theory with a small parameter of the theory proportional to the filling factor multiplied by the phase space filling factor. The energy spectrum of the collective elementary excitations is characterized by the interconnection of the exciton and plasmon branches, because the plasmon-type elementary excitations are gapless and are lying in the same spectral interval as the exciton-type elementary excitations.
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| 170997. |
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| 170998. |
- Moskalenko, S. A., et al.
(författare)
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Exciton Condensation Under High Magnetic Field
- 2011
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Ingår i: Journal of Nanoelectronics and Optoelectronics. - : American Scientific Publishers. - 1555-130X .- 1555-1318. ; 6:4, s. 393-419
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Forskningsöversikt (refereegranskat)abstract
- The new results in the theory of Bose-Einstein condensation (BEC) of the two-dimensional (2D) magnetoexcitons formed by the high-density electron-hole (e-h) pairs created on the semiconductor mono-layer in a strong perpendicular magnetic field are reviewed. One of them is the metastable dielectric liquid phase (MDLP) formed by the 2D magnetoexcitons BEG-ed on the single-particle state with sufficiently large values of the wave vector k, so that its product kl with the magnetic length l equals about kl approximate to 3-4. This state was revealed in the conditions when the electrons and holes are situated on the lowest Landau levels (LLLs) and the polarizability of the Bose gas was calculated on the base of the Anderson-type coherent excited states. They give rise to correlation energy and to chemical potential displaying a nonmonotonous dependence on the filling factor v(2) with a relative minimum and with positive compressibility in its vicinity. The influence of the excited Landau levels (ELLs) on the quantum states of the e-h system is due to the virtual quantum transitions of particles from the LLLs to ELLs during the Coulomb scattering processes and to their subsequent return back. These quantum transitions were taken into account in the frame of the second order perturbation theory giving rise to an effective Hamiltonian describing the supplementary indirect interactions between the particles lying on the LLLs. This interaction is characterized by a small parameter equal to the ratio r of the magnetoexciton ionization potential l(ex)(0) to the Landau quantization energy (h) over bar omega(c). The parameter r = l(ex)(0)/(h) over bar omega(c), decreases as H-1/2 with the increasing the magnetic field strength H. The supplementary interaction is attractive, making the magnetoexcitons in the Hartree approximation more robust. Nevertheless its exchange, Fock terms as well as the Bogoliubov u-v transformation terms give rise to positive, repulsion-type contributions to the chemical potential. The Bose gas of magnetoexcitons with k = 0 becomes weakly nonideal when the ELLs are taken into account. The collective elementary excitations of two ground states corresponding to BEG-ed magnetoexcitons forming either a nonideal Bose gas with k = 0 or the MDLP with kl approximate to 3-4 were studied in the frame of the perturbation theory with the infinitesimal parameter v(2)(1 - v(2)), chosen as a product of the filling factor v(2) and of the phase space filling factor (1 - v(2)). The collective elementary excitations in both cases consist from the exciton and plasmon branches. Due to the presence of the condensate there are energy and quasi-energy branches. The self-energy parts containing the unknown frequency in denominators increase the degree of the dispersion equations and give rise to mixed exciton-plasmon and exciton-exciton elementary excitation branches.
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| 170999. |
- Moskalenko, S. A., et al.
(författare)
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Exciton-cyclotron resonance in two-dimensional structures in a strong perpendicular magnetic field and optical orientation conditions
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:12, s. 125425-
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Tidskriftsartikel (refereegranskat)abstract
- The absorption band shapes of the combined optical quantum transitions with creation of the two-dimensional magnetoexcitons and simultaneous excitation of one background electron from its lowest to the first-excited Landau level by circularly polarized radiation under the conditions of optical orientation and spin polarization are investigated. The light absorption in the frame of dipole-active transition is described in the second-order perturbation theory taking into account as the perturbations the electron-photon interaction and the electron-electron Coulomb interaction. The Hamiltonian of the electron-photon interaction depends on the directions of the light propagation and its circular polarization relative to the magnetic field direction and the electron-heavy-hole alignment with regard to the plane of the layer. It is shown that the probability of the combined absorption rate is four times larger if the optically created electron has the same spin projection as the background electrons, compared to the case when the electrons have antiparallel spins. The probability of quantum transition and the absorption band peaks decrease with the increased magnetic field as H-1/2 at a given filling factor v(2). If photocreated electron and hole have the same numbers of the Landau levels, n(e)=n(h), the quantum transitions are dipole active. If these numbers differ by one, the quantum transition is quadrupole active, depends on the projections of the light wave vector on the plane of the layer, and vanishes in the Faraday geometry.
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| 171000. |
- Moskalenko, S. A., et al.
(författare)
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Influence of excited Landau levels on a two-dimensional electron-hole system in a strong perpendicular magnetic field
- 2006
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 140:5, s. 236-239
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Tidskriftsartikel (refereegranskat)abstract
- The study of the quantum states of a two-dimensional electron-hole system in a strong perpendicular magnetic field is carried out with special attention to the influence of virtual quantum transitions of interacting particles between the Landau levels. These virtual quantum transitions from the lowest Landau levels to excited Landau levels with arbitrary quantum numbers n and m and their reversion to the lowest Landau levels in second order perturbation theory result in an indirect attraction between the particles. The influence of the indirect interaction on the magnetoexciton ground state, on the chemical potential of the Bose-Einstein condensed magnetoexcitons, and on the ground state energy of the metallic-type electron-hole liquid is investigated in the Hartree-Fock approximation. The coexistence of different phases is suggested.
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