Mott transition of excitons in GaAs-GaAlAs quantum wells

Manzke, G.; Semkat, D.; Stolz, H.

doi:10.1088/1367-2630/14/9/095002

Cited by 32 publications

(33 citation statements)

References 53 publications

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“…[25] with special attention to the influence of many-particle effects such as screening and lowering of the ionization energy. The dissociation of excitons in GaAs-GaAlAs quantum wells with increasing excitation was studied within two different theoretical approaches [26]. From a thermodynamic approach a simple criterion for the transition to the EHP was obtained: the sum of chemical potentials of carriers, reflecting the effective shrinkage of the band edge, crosses the exciton energy with increasing excitation.…”

Section: Introductionmentioning

confidence: 99%

“…Alternatively, a spectral approach, based on the semiconductor Bloch equations within linear optical response, was used to analyze the quasiparticle properties of carriers and the dynamical screening between electron-hole pairs. While the first is effectively a one-particle approach, in the second the whole two-particle spectrum is studied [26]. The transition between the excitons and the EHP was obtained in Hartree-Fock approximation for QWs [26].…”

Section: Introductionmentioning

confidence: 99%

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On the phase diagram of a two-dimensional electron–hole system

Berman

Kezerashvili

Ziegler

2015

Physica E: Low-dimensional Systems and Nanostructures

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A first order phase transition between a BCS phase and an insulating Mott phase for a gas of spatially separated electrons and holes with tunable Coulomb interaction and variable density is predicted. In the framework of a BCS-like mean-field approach and a Landau expansion in terms of the pairing order parameter the phase diagram is studied. This indicates several phases and phase transitions, including an electron-hole plasma at low density and weak interaction, an intermediate BCS phase with Cooper pairs and an electron-hole plasma at high density and weak interaction. The insulating Mott phase appears for the strong interaction and low temperatures. We briefly discuss the possibilities to realize these phases in realistic systems such as coupled quantum wells and graphene double layers.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the phase diagram of a two-dimensional electron–hole system

Berman

Kezerashvili

Ziegler

2015

Physica E: Low-dimensional Systems and Nanostructures

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“…This drawback can be circumvented in 2D systems. Here, most of the studies suggest a rather smooth MT [10][11][12][13]. On the contrary, experimental studies concerning the T dependence of the MT are extremely scarce.…”

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confidence: 99%

“…This is a purely fermionic effect which excludes excitonic absorption at the band edge. (ii) The crossing E X = E BGR , where the exciton merges with the continuum states and E b X vanishes [12,32]. Both criteria are depicted by the scheme of Fig.…”

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confidence: 99%

High-temperature Mott transition in wide-band-gap semiconductor quantum wells

et al. 2014

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The crossover from an exciton gas to an electron-hole plasma is studied in a GaN/(Al,Ga)N single quantum well by means of combined time-resolved and continuous-wave photoluminescence measurements. The twodimensional Mott transition is found to be of continuous type and to be accompanied by a characteristic modification of the quantum well emission spectrum. Beyond the critical density, the latter is strongly influenced by band-gap renormalization and Fermi filling of continuum states. Owing to the large binding energy of excitons in III-nitride heterostructures, their injection-induced dissociation could be tracked over a wide range of temperatures, i.e., from 4 to 150 K. Various criteria defining the Mott transition are examined, which, however, do not lead to any clear trend with rising temperature: the critical carrier density remains invariant around 10 12 cm −2 . At sufficiently low temperature T and carrier density n, free electrons and holes in a semiconductor bind and form neutrally charged quasiparticles. These so-called excitons represent the fundamental electronic excitation of a semiconductor and obey Bose statistics in the low-density limit. However, when increasing T or n beyond a certain limit, the exciton complexes get ionized and the system switches from an insulating state to a conductive electron-hole plasma (EHP)-the Mott transition (MT) [1]. While exciton dissociation induced by a hot phonon bath represents a classical process and occurs when the thermal energy becomes of the order of the exciton binding energy E b X ≈ k B T , the breakup of excitons due to an increasing carrier population relies on much more complex mechanisms. In simplified terms, when n approaches the hard-sphere limit, that is, when the interparticle distance is reduced to the order of the exciton Bohr radius a B , the fermionic properties of the exciton constituents become dominant: Coulomb screening and phase-space filling cause a reduction of E b X and eventually the dissociation of the excitonic bound state around a certain critical density n crit [2]. Note that the latter is usually overestimated by the simple hard-sphere criterion [3].Whereas the MT was initially claimed to be a first-order phase transition [1,4], later experiments led to partially conflicting results. Especially in three dimensions (3D), studies exist that argue to evidence the first-order nature of the MT [5,6], while others point toward a second-order transition [7][8][9]. However, note that in optically-probed bulk systems, the exponential absorption profile leads to an emission signal that mixes inhomogeneously injected regions and may conceal certain characteristics of the MT. This drawback can be circumvented in 2D systems. Here, most of the studies suggest a rather smooth MT [10][11][12][13]. On the contrary, experimental studies concerning the T dependence of the MT are extremely scarce. In a simple framework, an increasing Debye-screening length gives reason to expect a rise in n crit with T . Even if such a behavior was claimed for bulk ...

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“…Furthermore, we note, that for frequency independent absorption, equation (18) reduces to the known scaled version of the correlation functions…”

Section: General Correlation Functionsmentioning

confidence: 98%

Enhanced squeezing by absorption

Grünwald¹,

Vogel²

2016

Phys. Scr.

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Abstract. Absorption is usually expected to be detrimental to quantum coherence effects. However, the situation for complex absorption spectra has been little studied yet. We consider the resonance fluorescence of excitons in a semiconductor quantum well. The creation of excitons requires absorption of the incoming pump-laser light. Thus, the absorption spectrum of the medium acts as a spectral filter for the emitted light. Surprizingly, absorption can even improve quantum effects, as is demonstrated for the squeezing of the resonance fluorescence of the quantum-well system. This effect can be explained by an improved phase matching due to absorption.

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Mott transition of excitons in GaAs-GaAlAs quantum wells

Cited by 32 publications

References 53 publications

On the phase diagram of a two-dimensional electron–hole system

On the phase diagram of a two-dimensional electron–hole system

High-temperature Mott transition in wide-band-gap semiconductor quantum wells

Enhanced squeezing by absorption

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