Condensation of Indirect Excitons in Coupled AlAs/GaAs Quantum Wells

Butov, L. V.; Zrenner, A.; Abstreiter, G.; Böhm, G.; Weimann, G.

doi:10.1103/physrevlett.73.304

Cited by 355 publications

(213 citation statements)

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“…The onset of spontaneous coherence was evidenced by a strong enhancement of the recombination [25] and tunneling [26] rate, respectively. The results of other transport and optical experiments were also consistent with spontaneous coherence of indirect excitons [24,25,[27][28][29][30][31][32][33]. However, no direct measurement of coherence has been performed in these studies.…”

supporting

confidence: 69%

Spontaneous coherence in a cold exciton gas

High¹,

Leonard²,

Hammack³

et al. 2012

Nature

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299

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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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supporting

confidence: 69%

Spontaneous coherence in a cold exciton gas

High¹,

Leonard²,

Hammack³

et al. 2012

Nature

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307

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“…In these structures, the band alignments are such that electrons and holes are spatially separated in equilibrium, as the bottom of the conduction band on one side of the heterojunction lies lower than the top of the valence band on the other. Butov et al 10 have reported photoluminescence experiments in AlAs/GaAs heterojunctions, and their results suggest the appearance of a Bose condensate in at least the high magnetic field regime. Kono et al have also reported interesting spectroscopic data suggesting an infraredactive state in the InAs/Al x Ga 1−x Sb system with unusual properties, reminiscent also of those of a condensate.…”

Section: Introductionmentioning

confidence: 99%

Interaction potential between dynamic dipoles: Polarized excitons in strong magnetic fields

Olivares-Robles

Ulloa

2001

Phys. Rev. B

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The interaction potential of a two-dimensional system of excitons with spatially separated electron-hole layers is considered in the strong magnetic field limit. The excitons are assumed to have free dynamics in the x-y plane, while being constrained or 'polarized' in the z direction. The model simulates semiconductor double layer systems under strong magnetic field normal to the layers. The residual interaction between excitons exhibits interesting features, arising from the coupling of the center-of-mass and internal degrees of freedom of the exciton in the magnetic field. This coupling induces a dynamical dipole moment proportional to the center-of-mass magnetic moment of the exciton. We show the explicit dependence of the inter-exciton potential matrix elements, and discuss the underlying physics. The unusual features of the interaction potential would be reflected in the collective response and non-equilibrium properties of such system.

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“…The condensation of an exciton gas in semiconductors has been extensively discussed in the literature [39,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56]. The transition takes place when the system meets the so-called quantum degeneracy criterion nX D > 1.…”

Section: Bose-einstein Condensation and Coherent Control Of Excitomentioning

confidence: 99%

“…The finite lifetime of excitons represents an obvious drawback to achieve condensation. However, we note that typical lifetimes are long enough for the excitons to reach a quasi thermodynamic equilibrium, which can be studied using timeresolved techniques [47].…”

Section: Bose-einstein Condensation and Coherent Control Of Excitomentioning

confidence: 99%

Control of Electron Coherences with Coherent Phonons

Merlín¹

2000

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Condensation of Indirect Excitons in Coupled AlAs/GaAs Quantum Wells

Cited by 355 publications

References 20 publications

Spontaneous coherence in a cold exciton gas

Spontaneous coherence in a cold exciton gas

Interaction potential between dynamic dipoles: Polarized excitons in strong magnetic fields

Control of Electron Coherences with Coherent Phonons

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