105 research outputs found

    The Interaction in the Macroscopically Ordered Exciton State

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    The macroscopically ordered exciton state (MOES) - a periodic array of beads with spatial order on a macroscopic length - appears in the external exciton rings at low temperatures below a few Kelvin. Here, we report on the experimental study of the interaction in the MOES. The exciton PL energy varies in concert with the intensity along the circumference of the ring, with the largest energy found in the brightest regions. This shows that the MOES is characterized by the repulsive interaction and is not driven by the attractive interaction.Comment: 3 pages, 3 figure

    S- and P-polarized reflectivities of strongly correlated plasma

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    Charge transport and phase transition in exciton rings

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    The macroscopic exciton rings observed in the photoluminescence (PL) patterns of excitons in coupled quantum wells (CQWs) are explained by a series of experiments and a theory based on the idea of carrier imbalance, transport and recombination. The rings are found to be a source of cold excitons with temperature close to that of the lattice. We explored states of excitons in the ring over a range of temperatures down to 380 mK. These studies reveal a sharp, albeit continuous, second order phase transition to a low-temperature ordered exciton state, characterized by ring fragmentation into a periodic array of aggregates. An instability at the onset of degeneracy in the cold exciton system, due to stimulated exciton formation, is proposed as the transition mechanism.Comment: 8 pages including 4 figure

    Electrical conductivity of plasmas of DB white dwarf atmospheres

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    The static electrical conductivity of non-ideal, dense, partially ionized helium plasma was calculated over a wide range of plasma parameters: temperatures 1104KT1105K1\cdot 10^{4}\textrm{K} \lesssim T \lesssim 1\cdot 10^{5}\textrm{K} and mass density 1×106g/cm3ρ2g/cm31 \times 10^{-6} \textrm{g}/\textrm{cm}^{3} \lesssim \rho \lesssim 2 \textrm{g}/\textrm{cm}^{3}. Calculations of electrical conductivity of plasma for the considered range of plasma parameters are of interest for DB white dwarf atmospheres with effective temperatures 1104KTeff3104K1\cdot 10^{4}\textrm{K} \lesssim T_{eff} \lesssim 3\cdot 10^{4}\textrm{K}. Electrical conductivity of plasma was calculated by using the modified random phase approximation and semiclassical method, adapted for the case of dense, partially ionized plasma. The results were compared with the unique existing experimental data, including the results related to the region of dense plasmas. In spite of low accuracy of the experimental data, the existing agreement with them indicates that results obtained in this paper are correct

    Magneto optics of the spatially separated electron and hole layers in GaAs=AlGaAs coupled quantum wells

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    Abstract We report on the photoluminescence (PL) study of the spatially separated electron and hole layers in GaAs=AlGaAs coupled quantum wells at low temperatures T ¿50 mK. At high magnetic ÿelds cusps are observed in the energy and intensity of the indirect (interwell) exciton PL. We tentatively attribute these to the commensurability e ects of the magnetoexciton with island structures in the sample. Strong nonlinearities in the indirect exciton PL kinetics are observed: right after the excitation is switched o , the indirect exciton PL intensity jumps up, and the consequent PL intensity decay rate increases strongly with excitation density. The e ects can be attributed to stimulated exciton scattering to the optically active exciton states (the boser e ect) and exciton superradiance. ? 2000 Elsevier Science B.V. All rights reserved. Keywords: Magneto optics; Coupled quantum wells The system of spatially separated electron (e) and hole (h) layers in coupled quantum wells (CQWs) is remarkable by the fact that because of much longer e-h recombination time compared to single-layer e-h systems one can reach lower e-h temperatures that are close to the lattice temperature. Therefore, CQWs provide a unique opportunity for studying low-temperature 2D neutral e-h systems. * Correspondence address: Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia. Fax: +7-096-576-4111. We report on the cw and time-resolved photoluminescence (PL) study of the spatially separated e and h layers in GaAs=AlGaAs CQW at low-temperatures T ¿50 mK and high magnetic ÿelds B616 T. The electric-ÿeld-tunable n + − i − n + GaAs=AlGaAs CQW structure was grown by MBE. The i-region consists of two 8 nm GaAs QWs separated by a 4 nm Al 0:33 Ga 0:67 As barrier and surrounded by two 200 nm Al 0:33 Ga 0:67 As barrier layers. The n + -layers are Si-doped GaAs with N Si = 5 × 10 17 cm −3 . The electric ÿeld in the z-direction is monitored by the external gate voltage V g applied between n + -layers. The small disorder in the CQW is indicated by the 1386-9477/00/$ -see front matter ? 2000 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 6 -9 4 7 7 ( 9 9 ) 0 0 1 4 5 -
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