Charge Separation of Dense Two-Dimensional Electron-Hole Gases: Mechanism for Exciton Ring Pattern Formation

Rapaport, Ronen; Chen, Gang; Snoke, D. W.; Simon, Steven H.; Pfeiffer, L. N.; West, K. W.; Liu, Y.; Denev, S.

doi:10.1103/physrevlett.92.117405

Cited by 146 publications

(148 citation statements)

References 7 publications

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“…Exciton rings, including the inner ring, external ring, and localized bright spot (LBS) rings were observed earlier [37]. The external and LBS rings are exciton sources that form on the boundaries between electron-rich and hole-rich regions; the former is created by current through the structure (specifically, by the current filament at the LBS center in the case of the LBS ring), while the latter is created by optical excitation [38][39][40][41]. Figure 1c shows a segment of the exciton emission pattern with a section of the external ring and smaller LBS rings.…”

Section: Methodsmentioning

confidence: 99%

Spontaneous coherence in a cold exciton gas

High¹,

Leonard²,

Hammack³

et al. 2012

Nature

306

307

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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

306

307

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show abstract

“…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: 98%

“…To study the problem of exciton condensation afterwards, we use the results of calculations of the exciton generations rate G, obtained in [3,4,6]. As it is shown in Refs.…”

Section: Model Of the Systemmentioning

confidence: 99%

“…The distribution of electrons and holes in a double QW plane is described by diffusion equations [3,4]. To study the problem of exciton condensation afterwards, we use the results of calculations of the exciton generations rate G, obtained in [3,4,6].…”

Section: Model Of the Systemmentioning

confidence: 99%

“…The mechanism of ring appearance was suggested in [3,4] basing on two assumptions: (1) without light irradiation the well is populated with a certain density of electrons; (2) holes are captured by the well with a larger probability than electrons. As the result of charge separation, the irradiated structure divides into two differently charged spatial regions: holes nearby the central spot and electrons far from it.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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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Manipulating luminescence in semiconductor nanostructures via field‐effect‐tuneable potentials

Kotthaus

2006

Physica Status Solidi (b)

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The luminescence properties of III -V quantum wells under the influence of field-effect-tuneable and laterally modulated potentials are reviewed. Large electric fields generated in the quantum well plane cause a modulation of the quantum well absorption via the Franz -Keldysh effect as well as a reversible separation of optically excited electron -hole pairs. The electron -hole pair separation by field effect can prolong the recombination lifetimes by many orders of magnitude and yields a controllably delayed reemission of luminescence radiation. Dynamic in-plane electric fields caused by the propagation of surface acoustic waves on piezoelectric heterostructures make possible spatially and temporarily delayed luminescence whereas a two-dimensional modulation of the electrostatic potential enables the delayed storage of optical images. Spatial modulation of the quantum confined Stark effect via the out-of-plane electric field is employed to realize tuneable excitonic traps and to study macroscopic transport of long-living, spatially indirect excitons in suitably designed double quantum wells. This is possibly paving the way for the observation of excitonic Bose -Einstein condensation in quantum well structures.

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Charge Separation of Dense Two-Dimensional Electron-Hole Gases: Mechanism for Exciton Ring Pattern Formation

Cited by 146 publications

References 7 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

Manipulating luminescence in semiconductor nanostructures via field‐effect‐tuneable potentials

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