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

Ivanov, A. L.; Smallwood, L. E.; Hammack, A. T.; Yang, Sen; Butov, L. V.; Gossard, A. C.

doi:10.1209/epl/i2006-10002-4

Cited by 87 publications

(201 citation statements)

References 23 publications

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“…In contrast to the external and LBS rings, the intensity profile along the inner ring was smooth 9 and no intensity modulation was reported in the inner ring until this work. In this article, we present observations of radial and azimuthal modulation of the emission intensity of indirect excitons in the inner ring.…”

Section: Introductionmentioning

confidence: 67%

“…7,9,17,18,26,28,29 For a strong laser excitation, the density of generated excitons is high so that they can effectively screen the disorder potential, delocalize, and travel and cool to the lattice temperature outside the laser excitation spot thus forming the inner ring. 7,9,17,18,26,28,29 Figures 1 The external ring can also be seen beyond the inner ring; the external ring radius (that is the distance to the excitation line for the studied case of line excitation) quickly increases with the excitation power. E pump = E probe = 1960 meV.…”

Section: A Experimentsmentioning

confidence: 99%

“…10,13,24,27 A set of exciton transport phenomena was observed, including the transistor effect for excitons, 14,15,19,21 localizationdelocalization transition in random potentials 7,9,10,13,17,22 and in static and moving lattices, 18,23,29 and the inner ring in emission patterns. 7,9,17,18,26,28,29,32 The studies of the latter form the subject of this work.…”

Section: Introductionmentioning

confidence: 99%

“…When excitons travel away from the excitation spot they thermalize to the lattice temperature so that the emission intensity increases outside of the excitation spot forming the inner ring. 7,9,17,18,26,28,29 Besides the inner ring, the external ring can be observed around the excitation spot 7,[36][37][38][39][40][41][42][43][44] and localized bright spot (LBS) rings can be observed around localized carrier sources. 7,36,[40][41][42][43]45 The external and LBS rings form on the boundaries between electron-rich and hole-rich regions; the former is created by current through the structure and the latter is created by optical excitation.…”

Section: Introductionmentioning

confidence: 99%

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Pattern formation in the exciton inner ring

et al. 2013

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We report on the two-beam study of indirect excitons in the inner ring in the exciton emission pattern. One laser beam generates the inner ring and a second weaker beam is positioned in the inner ring. The beam positioned in the inner ring is found to locally suppress the exciton emission intensity. We also report on the inner ring fragmentation and formation of multiple rings in the inner ring region. These features are found to originate from a weak spatial modulation of the excitation beam intensity in the inner ring region. The modulation of exciton emission intensity anticorrelates with the modulation of the laser excitation intensity. The three phenomena-inner ring fragmentation, formation of multiple rings in the inner ring region, and emission suppression by a weak laser beam in the inner ring-have a common feature: a reduction of exciton emission intensity in the region of enhanced laser excitation. This effect is explained in terms of exciton transport and thermalization.

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Section: Introductionmentioning

confidence: 67%

Section: A Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pattern formation in the exciton inner ring

et al. 2013

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“…The photoexcited electrons recombine within the inner ring [42,43]. Therefore, in the area of external and LBS rings with no photoexcited electrons coherence forms spontaneously; it is not affected by coherence of the optical pumping.…”

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

Cited by 87 publications

References 23 publications

Pattern formation in the exciton inner ring

Pattern formation in the exciton inner ring

Spontaneous coherence in a cold exciton gas

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

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