Charged Excitons in the Fractional Quantum Hall Regime

Yusa, Go; Shtrikman, Hadas; Bar‐Joseph, I.

doi:10.1103/physrevlett.87.216402

Cited by 115 publications

(138 citation statements)

References 27 publications

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“…Also the predicted singlettriplet crossing was reported recently [34]. In this paper we summarize our results [7], which, concerning the PL experiments are consistent with the observations of Yusa et al [6], i.e., (i) we observe a charged exciton at very low temperatures, which is not present in the spectrum at T = 2 K, (ii) this exciton occurs for filling factor ν < 1/3 only, i.e., related to the fractional quantum Hall effect (FQHE) regime, and (iii) the PL intensity of this excitation is of similar strength to that of the singlet exciton. Figure 2 shows a comparison of left-circularly polarized PL spectra, which were recorded at T = 2 K (upper spectrum), and at T = 0.1 K (lower spectrum).…”

Section: Methodssupporting

confidence: 81%

“…In a subsequent work, Szlufarska et al found that in asymmetric quantum wells the singlet-triplet crossing can be at considerably lower fields [33]. In experiments at very low temperatures the dark triplet exciton was identified by Yusa et al [6] and Schüller et al [7]. Also the predicted singlettriplet crossing was reported recently [34].…”

Section: Methodsmentioning

confidence: 85%

“…Instead, a saturation of the X − t binding energy was found at high fields [11,14,31,32]. Recent theoretical [19] and experimental work [6,7] solved this puzzle. It was found [19] that at high magnetic field two different triplet excitons exist as bound states.…”

Section: Methodsmentioning

confidence: 95%

“…The past decades have shown that optical experiments, like photoluminescence (PL) spectroscopy, can provide further and in some sense complementary information about the ground state of quantum Hall systems [1][2][3][4][5][6][7][8][9]. In fact, in optical experiments one is able to probe the bulk of a quantum Hall system, whereas transport is mostly governed by edge channels.…”

Section: Introductionmentioning

confidence: 99%

“…However, one of the striking differences of optical experiments, compared to transport, is the presence of photoexcited holes in the system, which can significantly influence its properties. In samples with very low carrier concentration, the Coulomb interaction between electrons and holes leads to the formation of negatively charged excitons, which have been a subject of intense research during the past decade (see, e.g., [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]). For samples with relatively strong disorder, the commonly accepted picture is that at low density the two-dimensional electron system (2DES) breaks up into areas with finite density (electron puddles) and completely depleted regions, where neutral excitons (X 0 ) can form.…”

Section: Introductionmentioning

confidence: 99%

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Charged Excitons in the Quantum Hall Regime

et al. 2004

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We review our recent optical experiments on two-dimensional electron systems at temperatures below 1 K and under high magnetic fields. The two-dimensional electron systems are realized in modulation-doped GaAsAlGaAs single quantum wells. Via gate electrodes the carrier density of the two-dimensional electron systems can be tuned in a quite broad range between about 1 × 10 10 cm −2 and 2 × 10 11 cm −2 . In dilute two-dimensional electron systems, at very low electron densities, we observe the formation of negatively charged excitons in photoluminescence experiments. In this contribution we report about the observation of a dark triplet exciton, which is observable at temperatures below 1 K and for electron filling factors < 1/3, i.e., in the fractional quantum Hall regime only. In experiments where we have increased the density of the two-dimensional electron systems so that a uniform two-dimensional electron system starts to form, we have found a strong energy anomaly of the charged excitons in the vicinity of filling factor 1/3. This anomaly was found to exist in a very narrow parameter range of the density and temperature, only. We propose a model where we assume that localized charged excitons and a uniform Laughlin liquid coexist. The localized charged exciton in close proximity to the Laughlin liquid leads to the creation of a fractionally-charged quasihole in the liquid, which can account for the experimentally observed anomaly.

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Section: Methodssupporting

confidence: 81%

Section: Methodsmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Charged Excitons in the Quantum Hall Regime

et al. 2004

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Linear and ultrafast optical spectroscopy in the regime of the quantum Hall effect

Broocks¹,

Su²,

Schröter³

et al. 2008

Physica Status Solidi (b)

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We review our optical experiments on two‐dimensional electron systems (2DES) of different mobilities, realized in modulation‐doped GaAs–AlGaAs single quantum wells, in quantizing magnetic fields. The carrier densities of the 2DESs could be tuned in a quite broad range between about 1 × 1010 cm–2 and 2 × 1011 cm–2 via gate electrodes. In photoluminescence (PL) and absorption experiments on 2DES with moderate mobility, at very low electron densities, we have observed the formation of negatively charged excitons. In these experiments, we could identify a dark triplet exciton, which is observable at temperatures below 1 K and for electron filling factors v < 1/3 i.e., in the fractional quantum Hall regime, only. In experiments where we have increased the density of the 2DES so that a uniform 2DES starts to form, we have found a strong energetic anomaly of the charged excitons in the vicinity of filling factor 1/3. The anomaly could be explained by a model, assuming that at very low temperatures localized charged excitons and a uniform Laughlin liquid coexist. Furthermore, we report on ultrafast optical experiments at the v = 1 quantum Hall state of a high‐mobility 2DES in a GaAs–AlGaAs single quantum well. By spectrally‐resolved four‐wave‐mixing experiments, we have investigated the coherent dynamics of photo‐excited electron–hole pairs and found extraordinarily long decoherence times for electrons, excited into the upper spin level, around v = 1 We attribute the observed faster decay of the dephasing time for v < 1 as compared to v > 1 presumably to the coherent coupling of the spin levels via spin waves. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Photoluminescence spectral evolution from 2DEG‐free hole to charged excitons in modulation‐doped GaAs/AlGaAs quantum wells

Ashkinadze¹,

Rudenkov

Christianen

et al. 2004

phys. stat. sol. (c)

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We report on a detailed study of the photoluminescence (PL) in high quality GaAs/AlGaAs quantum wells containing a two-dimensional electron gas. The 2DEG density was varied by optical depletion (with He-Ne laser illumination) in the range of n 2D = (7-3) × 10 10 cm -2 . The n 2D -dependent PL spectra were studied under a perpendicularly applied magnetic field B < 12 T at T L = 0.3 and 1.5 K. The evolution from free hole-2DEG to charged exciton PL with decreasing n 2D or with increasing magnetic field is attributed to the appearance of regions containing localized electrons as the filling factor decreases below ν = 0.4-0.3. This results in simultaneous PL of the free hole-2DEG originating from electron puddles and of charged exciton from regions with localized electrons.The remarkable transport properties of the two dimensional electron gas (2DEG) in the quantum Hall regime have stimulated an extensive investigation of the photoluminescence (PL) in modulation-doped quantum wells (MDQWs) under a perpendicularly applied magnetic field [1][2][3][4][5]. Intensity and energy oscillations of the free hole-2DEG PL lines were observed at integer and fractional filling factors ν in modulation-doped GaAs/AlGaAs heterostructures when the separation between the photoexcited valence hole and the 2DEG layer, d eh , exceeds the average electron-electron distance n 2D -1/2 (n 2D is the 2DEG density) or the magnetic lengthVarious theories predict that the PL, in this case, is a sensitive probe of the many-body interaction in the magnetized 2DEG [6][7][8].In the opposite case, d eh < L B , the Coulomb interaction of the photoexcited valence hole with the electrons affects the 2DEG properties. This is expected for MDQW's having n 2D < 10 11 cm -2 since the built-in electrical field is too weak to separate the hole from the 2D-electrons even in wide (20-30nm) MDQWs [9]. One of the most remarkable features of the low-temperature PL spectrum of MDQWs is the appearance of high-energy PL bands at filling factors ν < 1 [1]. Previously, these PL bands were attributed to the radiative recombination of the hole with fractionally charged 2DEG quisiparticles. Then, they were associated with neutral and negatively charged excitons, X 0 and X -, respectively [10, 11 and refs. there]. The X -complex consists of two electrons and a hole, and in a magnetic field, two bound states, X s --spin-singlet and X t --spin-triplet, can be formed. The lowest energy X t -is a "dark" state [12], and it can emit light either if it is localized or it is scattered by disorder or by 2D-electrons [11,12]. Recently, a splitting of the high-energy, broad PL band into two PL lines was observed at ν < 1/3, and these lines

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Charged Excitons in the Fractional Quantum Hall Regime

Cited by 115 publications

References 27 publications

Charged Excitons in the Quantum Hall Regime

Charged Excitons in the Quantum Hall Regime

Linear and ultrafast optical spectroscopy in the regime of the quantum Hall effect

Photoluminescence spectral evolution from 2DEG‐free hole to charged excitons in modulation‐doped GaAs/AlGaAs quantum wells

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