Excitonic condensation in quasi-two-dimensional systems

We present a low energy model for the Bose-Einstein condensation in a quasi-two-dimensional excitonic gas. Using the flow equations of the Renormalization group and a $\Phi^4$ model with the dynamical critical exponent $z=2$ we calculate the temperature dependence of the critical density, coherence length, magnetic susceptibility, and specific heat. The model can be relevant for the macroscopic coherence observed in GaAs/AlGaAs coupled quantum wells.Comment: 4 Revtex page

On the microscopic theory of the exciton ring fragmentation

The description is presented for the dependence of the indirect exciton condensate density at the ring as a function of the polar angle at zero temperature with the involvement of the processes of formation and recombination of the excitons. In particular, starting from the quasi one-dimensional Gross-Pitaevskii equation with a spatially uniform generating term, we derive an exact analytical solution yielding the fragmentation of an exciton ring which is probably observed in the experiments.Comment: 4 pages, 1 figure. The preprint has been brought into accord with the journal's varian

Dynamics of Long-Living Excitons in Tunable Potential Landscapes

A novel method to experimentally study the dynamics of long-living excitons in coupled quantum well semiconductor heterostructures is presented. Lithographically defined top gate electrodes imprint in-plane artificial potential landscapes for excitons via the quantum confined Stark effect. Excitons are shuttled laterally in a time-dependent potential landscape defined by an interdigitated gate structure. Long-range drift exceeding a distance of 150 um at an exciton drift velocity > 1000 m/s is observed in a gradient potential formed by a resistive gate stripe.Comment: 4 pages, 4 figures. To appear in Phys. E (MSS-12-Proceedings

Conditions and possible mechanism of condensation of e-h pairs in bulk GaAs at room temperature

A mechanism of the condensation of e-h pairs in bulk GaAs at room temperature, which has been observed earlier, is proposed. The point is that the photon assisted pairing happens in a system of electrons and holes that occupy energy levels at the very bottoms of the bands. Due to a very high e-h density, the destruction of the pairs and loss of coherency does not occur because almost all energy levels inside a 30-60 meV band from the bottom of the conduction band prove to be occupied. As a result, a coherent ensemble of composite bosons (paired electrons and holes) with the minimum possible energy appears. The lifetime of this strongly non-equilibrium coherent e-h BCS-like state is as short as a few hundred of femtosecondsComment: 10 pages, 8 figure

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Ellipses and hyperbolas of decomposition of even numbers into pairs of prime numbers

This is just an attempt to associate sums or differences of prime numbers with points lying on an ellipse or hyperbola. Certain pairs of prime numbers can be represented as radius-distances from the focuses to points lying either on the ellipse or on the hyperbola. The ellipse equation can be written in the following form: |p(k)| + |p(t)| = 2n. The hyperbola equation can be written in the following form: ||p(k)| - |p(t)|| = 2n. Here p(k) and p(t) are prime numbers (p(1) = 2, p(2) = 3, p(3) = 5, p(4) = 7,...), k and t are indices of prime numbers, 2n is a given even number, k, t, n ∈ N. If we construct ellipses and hyperbolas based on the above, we get the following: 1) there are only 5 non-intersecting curves (for 2n=4; 2n=6; 2n=8; 2n=10; 2n=16). The remaining ellipses have intersection points. 2) there is only 1 non-intersecting hyperbola (for 2n=2) and 1 non-intersecting vertical line. The remaining hyperbolas have intersection points. Will there be any new thoughts, ideas about this

Ellipses and hyperbolas of decomposition of even numbers into pairs of prime numbers

This is just an attempt to associate sums or differences of prime numbers with points lying on an ellipse or hyperbola. Certain pairs of prime numbers can be represented as radius-distances from the focuses to points lying either on the ellipse or on the hyperbola. The ellipse equation can be written in the following form: |p(k)| + |p(t)| = 2n. The hyperbola equation can be written in the following form: ||p(k)| - |p(t)|| = 2n. Here p(k) and p(t) are prime numbers (p(1) = 2, p(2) = 3, p(3) = 5, p(4) = 7,...), k and t are indices of prime numbers, 2n is a given even number, k, t, n ∈ N. If we construct ellipses and hyperbolas based on the above, we get the following: 1) there are only 5 non-intersecting curves (for 2n=4; 2n=6; 2n=8; 2n=10; 2n=16). The remaining ellipses have intersection points. 2) there is only 1 non-intersecting hyperbola (for 2n=2) and 1 non-intersecting vertical line. The remaining hyperbolas have intersection points. Will there be any new thoughts, ideas about this

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Origin of the inner ring in photoluminescence patterns of quantum well excitons

In order to explain and model the inner ring in photoluminescence (PL) patterns of indirect excitons in GaAs/AlGaAs quantum wells (QWs), we develop a microscopic approach formulated in terms of coupled nonlinear equations for the diffusion, thermalization and optical decay of the particles. The origin of the inner ring is unambiguously identified: it is due to cooling of indirect excitons in their propagation from the excitation spot. We infer that in our high-quality structures the in-plane diffusion coefficient is about 10-30cm^2/s and the amplitude of the disorder potential is about 0.45meV.Comment: 4 pages, 3 figure