Macroscopically ordered state in an exciton system

Butov, L. V.; Gossard, A. C.; Chemla, D. S.

doi:10.1038/nature00943

Cited by 517 publications

(680 citation statements)

References 20 publications

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“…Similar phenomena are observed in the external ring region. At low T , the MOES forms in the external ring [37] (Figs. 1c and 2e) and a periodic polarization texture forms around the periodic array of beads in the MOES [44] (Fig.…”

Section: Methodsmentioning

confidence: 99%

Spontaneous coherence in a cold exciton gas

High¹,

Leonard²,

Hammack³

et al. 2012

Nature

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306

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Excitons, bound pairs of electrons and holes, form a model system to explore the quantum physics of cold bosons in solids. Cold exciton gases can be realized in a system of indirect excitons, which can cool down below the temperature of quantum degeneracy due to their long lifetimes. Here, we report on the measurement of spontaneous coherence in a gas of indirect excitons. We found that extended spontaneous coherence of excitons emerges in the region of the macroscopically ordered exciton state and in the region of vortices of linear polarization. The coherence length in these regions is much larger than in a classical gas, indicating a coherent state with a much narrower than classical exciton distribution in momentum space, characteristic of a condensate. We also observed phase singularities in the coherent exciton gas. Extended spontaneous coherence and phase singularities emerge when the exciton gas is cooled below a few Kelvin. Spontaneous coherence of excitonsIf bosonic particles are cooled down below the temperature of quantum degeneracy they can spontaneously form a coherent state in which individual matter waves synchronize and combine. Spontaneous coherence of matter waves forms the basis for a number of fundamental phenomena in physics, including superconductivity, superfluidity, and Bose-Einstein condensation (BEC) [1][2][3][4][5]. Spontaneous coherence is the key characteristic of condensation in momentum space [6].Excitons are hydrogen-like bosons at low densities [7] and Cooper-pair-like bosons at high densities [8]. The bosonic nature of excitons allows for condensation in momentum space, i.e. emergence of spontaneous coherence. Designing semiconductor structures with required characteristics and controlling the parameters of the exciton system gives an opportunity to study various types of exciton condensates.A condensate of exciton-polaritons was recently realized in semiconductor microcavities [9][10][11][12][13]. This condensate is characterized by a strong coupling of excitons to the optical field and a short lifetime of the polaritons. Unlike BEC, equilibrium is not required for the polariton condensation and coherence in the polariton condensate forms due to a coherent optical field similar to coherence in lasers [14].There are intriguing theoretical predictions for a range of coherent states in cold exciton systems, including BEC [7], BCS-like condensation [8], charge-density-wave formation [15], and condensation with spontaneous timereversal symmetry breaking [16]. In these condensates, spontaneous coherence of exciton matter waves emerges below the temperature of quantum degeneracy.Since excitons are much lighter than atoms, quantum degeneracy can be achieved in excitonic systems at temperatures orders of magnitude higher than the microKelvin temperatures needed in atomic vapors [1, 2]. Exciton gases need be cooled down to a few Kelvin to enter the quantum regime. Although the temperature of the semiconductor crystal lattice T lat can be lowered well below 1 K in He-refrigerators, lower...

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Section: Methodsmentioning

confidence: 99%

Spontaneous coherence in a cold exciton gas

High¹,

Leonard²,

Hammack³

et al. 2012

Nature

Self Cite

306

307

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“…In this case, as it is shown in [5], spatial instability and inhomogeneous exciton distribution may emerge. This model has a problem with the correct prediction of the temperature of the ring fragmentation, because in the experiment [1] the fragmentation is observed at higher temperature (or at smaller exciton density) than the theory predicts. The model [6] was based on the traditional phase transition theory, generalized for the case of a non-equilibrium system, in which created particles (excitons) have finite lifetimes.…”

Section: Introductionmentioning

confidence: 98%

“…Indirect excitons have long lifetime, because electrons and holes are separated in the space. In AlGaAs and InGaAs double QW structures, a spot of the laser excitation was reported to be surrounded by a concentric bright ring separated from the laser spot by a dark intermediate region [1][2][3][4]. The distance between the ring and the spot grew with increasing the intensity of the pumping.…”

Section: Introductionmentioning

confidence: 99%

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Electron-Hole Distribution and Exciton Condensed Phase Formation in Semiconductor Quantum Wells

Chernyuk

Sugakov

2006

Acta Phys. Pol. A

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We study the development of ring luminescence of indirect excitons at macroscopical distances from the central excitation spot in quantum well structures. The Landau model for exciton condensation generalized for particles with finite lifetimes in conditions of inhomogeneous excitation is proposed. The transition between the fragmented and continuous rings and the temperature dependence of the effects are considered. The irradiation of the system by two spatially separated laser spots is simulated as well.

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“…First, optically generated indirect excitons in GaAs/AlGaAs systems have been studied, with a particular focus on macroscopic coherent ring-shaped patterns which suggest the presence of an excitonic condensate. [10][11][12] The second method is to induce an electron-hole (e-h) bilayer by doping and/or electrostatic gating. 13 This class of devices benefits from having independent ohmic contacts to the two layers, making it possible to use transport experiments to probe the state of the system.…”

mentioning

confidence: 99%

A complete laboratory for transport studies of electron-hole interactions in GaAs/AlGaAs ambipolar bilayers

Cumis

Waldie

Croxall

et al. 2017

Applied Physics Letters

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We present GaAs/AlGaAs double quantum well devices that can operate as both electron-hole (e-h) and hole-hole (h-h) bilayers, with separating barriers as narrow as 5 nm or 7.5 nm. With such narrow barriers, in the h-h configuration, we observe signs of magnetic-field-induced exciton condensation in the quantum Hall bilayer regime. In the same devices, we can study the zero-magnetic-field e-h and h-h bilayer states using Coulomb drag. Very strong e-h Coulomb drag resistivity (up to 10% of the single layer resistivity) is observed at liquid helium temperatures, but no definite signs of exciton condensation are seen in this case. Self-consistent calculations of the electron and hole wavefunctions show this might be because the average interlayer separation is larger in the e-h case than the h-h case.

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Macroscopically ordered state in an exciton system

Cited by 517 publications

References 20 publications

Spontaneous coherence in a cold exciton gas

Spontaneous coherence in a cold exciton gas

Electron-Hole Distribution and Exciton Condensed Phase Formation in Semiconductor Quantum Wells

A complete laboratory for transport studies of electron-hole interactions in GaAs/AlGaAs ambipolar bilayers

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