Some Remarks on the Ground State of the Exciton and Exciton-Polariton System

Littlewood, P. B.; Brown, G.; Eastham, P. R.; Szymańska, M. H.

doi:10.1002/1521-3951(200211)234:1<36::aid-pssb36>3.0.co;2-w

Cited by 11 publications

(6 citation statements)

References 31 publications

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“…The bi-excitonic ground state is similar to a helium atom in the sense that there are two positive and two negative Coulomb bound charges. These states can be identified as "excitonic molecule" states [4]. The calculated permanent electric dipole moment p = xρ(x)d 3 x for the exciton and bi-exciton of the lens-shaped dot D2 are aligned along (001) direction (growth direction), and amount to p z =3.58 eÅ for the exciton and p z =7.16 eÅ for the biexciton.…”

Section: Many-body Statesmentioning

confidence: 97%

“…At medium and high densities, where the QDs have stronger coupling, there could be numerous phases as a function of carrier density and mass ratios, as proposed in Ref. 4. In these regions, the picture of (bi-)exciton on a single QD is not valid anymore.…”

Section: Many-body Statesmentioning

confidence: 99%

“…an "excitonic ground state" as envisioned by Mott [1] and Keldysh et al [2]. Indeed, the electron-hole system exhibits a rich range of phases [3,4] as a function of the carrier density and effective-mass ratio m e /m h , including various excitonic insulating states such as molecular solid, exciton liquid, Mott insulator, and also various metallic phases. The excitonic ground state is of fundamental interest in itself because excitons can be a better alternative to atoms for studying Bose-Einstein condensation [5,6] on account of the lighter excitonic mass, thus higher condensation temperature.…”

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confidence: 99%

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Prediction of an Excitonic Ground State inInAs/InSbQuantum Dots

Bester

Zunger

2005

Phys. Rev. Lett.

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Using atomistic pseudopotential and configuration-interaction many-body calculations, we predict a metal-nonmetal transition and an excitonic ground state in the InAs/InSb quantum dot (QD) system. For large dots, the conduction band minimum of the InAs dot lies below the valence band maximum of the InSb matrix. Due to quantum confinement, at a critical size calculated here for various shapes, the single-particle gap Eg becomes very small. Strong electron-hole correlation effects are induced by the spatial proximity of the electron and hole wavefunctions, and by the lack of strong (exciton unbinding) screening, afforded by the existence of fully discrete 0D confined energy levels. These correlation effects overcome Eg, leading to the formation of a bi-excitonic ground state (two electrons in InAs and two holes in InSb) being energetically more favorable (by ∼ 15 meV) than the state without excitons. We discuss the excitonic phase transition on QD arrays in the low dot density limit. The formation of excitons in semiconductors and insulators usually requires energy, e.g. photons, for one has to excite carriers across the single-particle band-gap E g . There is a special interest, however, in the possibility of forming excitons exothermically, i.e. an "excitonic ground state" as envisioned by Mott [1] and Keldysh et al. [2]. Indeed, the electron-hole system exhibits a rich range of phases [3,4] as a function of the carrier density and effective-mass ratio m e /m h , including various excitonic insulating states such as molecular solid, exciton liquid, Mott insulator, and also various metallic phases. The excitonic ground state is of fundamental interest in itself because excitons can be a better alternative to atoms for studying Bose-Einstein condensation [5,6] on account of the lighter excitonic mass, thus higher condensation temperature. It is natural to search for excitonic ground states in systems where E g is small, yet the screening is weak enough so as to prevent unbinding of the exciton. The search in bulk solids [7] has thus focused on indirect gap semiconductors and semimetals to reduce screening, but excitonic ground states have not been conclusively observed so far in such systems. Ground state excitons were also searched in nanostructures, specifically in spatially indirect quantum-wells [8,9], where electrons and holes are confined in different spatial regions. In "type II" systems such as GaInAs/InP or CdTe/CdSe, electrons are localized in the well, whereas holes are localized on the barrier, so screening is weak, but E g is finite. In contrast, in "type III" heterostructures such as [10] InAs/GaSb, the conduction band minium (CBM) of the InAs well is lower than the valence band maximum (VBM) of the GaSb barrier, so at certain a well thickness one can have E g →0 [10], as well as separation of electrons from holes. Thus, at this thickness, one could expect an excitonic ground state if the electron-hole correlation energy will be large enough to stabilize the complex. Recent experiments [11] show evid...

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Section: Many-body Statesmentioning

confidence: 97%

Section: Many-body Statesmentioning

confidence: 99%

mentioning

confidence: 99%

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Prediction of an Excitonic Ground State inInAs/InSbQuantum Dots

Bester

Zunger

2005

Phys. Rev. Lett.

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“…The electron-hole system is surely one of the simplest model systems in condensed matter physics. The ground state(s) of this model are likely to include various kinds of quantum solids and liquids [41]. The relevant parameters are the density (measured by r s ), the mass ratio of electron to hole Γ = m e /m h , and, for 2D bilayers, the separation d. If Γ ≫ 1, then we are discussing hydrogen, where we expect that the two basic phases are either a molecular solid of H 2 , or at very high densities a metallic crystal -where the electrons delocalise.…”

Section: Possible Phases Of the Electron-hole Systemmentioning

confidence: 99%

Models of coherent exciton condensation

Littlewood¹,

Eastham²,

Keeling³

et al. 2004

J. Phys.: Condens. Matter

109

138

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That excitons in solids might condense into a phase-coherent ground state was proposed about 40 years ago, and has been attracting experimental and theoretical attention ever since. Although experimental confirmation has been hard to come by, the concepts released by this phenomenon have been widely influential. This tutorial review discusses general aspects of the theory of exciton and polariton condensates, focussing on the reasons for coherence in the ground state wavefunction, the BCS to Bose crossover(s) for excitons and for polaritons, and the relationship of the coherent condensates to standard lasers.

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“…Luminescence of these biexcitons, which are bound states of excitons (electron-hole pairs), is potentially relevant for studying luminescence from semiconductor lasers. While semiconductor lasers correspond to the dense limit of the electron-hole phase diagram, where the electrons and holes ionise into a plasma 1 , it is well known that the inclusion of correlation effects with the surrounding electrons and holes is necessary for a good estimate of semiconductor luminescence [2][3][4] . Moreover, a variational Monte Carlo study of the electron-hole phase diagram has revealed a surprisingly large excitonic insulator phase, which extends well into these high densities 5 .…”

Section: Introductionmentioning

confidence: 99%

Optical recombination of biexcitons in semiconductors

et al. 2013

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We calculate the photoluminescence spectrum and lifetime of a biexciton in a semiconductor using Fermi's golden rule. Our biexciton wavefunction is obtained using a Quantum Monte Carlo calculation. We consider a recombination process where one of the excitons within the biexciton annihilates. For hole masses greater than or equal to the electron mass, we find that the surviving exciton is most likely to populate the ground state. We also investigate how the confinement of excitons in a quantum dot would modify the lifetime in the limit of a large quantum dot where confinement principally affects the centre of mass wavefunction. The lifetimes we obtain are in reasonable agreement with experimental values. Our calculation can be used as a benchmark for comparison with approximate methods.Comment: 6 pages, 2 figure

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Some Remarks on the Ground State of the Exciton and Exciton-Polariton System

Cited by 11 publications

References 31 publications

Prediction of an Excitonic Ground State inInAs/InSbQuantum Dots

Prediction of an Excitonic Ground State inInAs/InSbQuantum Dots

Models of coherent exciton condensation

Optical recombination of biexcitons in semiconductors

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