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Charged Excitons in the Quantum Hall Regime

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Schüller C., Broocks K., Schröter P., Heyn C., Heitmann D., Bichler M., Wegscheider W., Apalkov V., Chakraborty T.

Acta Physica Polonica A

2004

vol. 106

issue 3

341-353

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 GaAs-AlGaAs 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.

Surfactant proteins SP-A and SP-D in human health and dis

100%

Kishore U., Lopez B. A., Kamran M. F., Saxena S., Singh M., Sarma P. U., Madan T., Chakraborty T.

Archivum Immunologiae et Therapiae Experimentalis

2005

vol. 53

issue 5

399-417

Surfactant proteins A (SP-A) and D (SP-D) are lung surfactant-associated hydrophilic proteins which have been implicated in surfactant homeostasis and pulmonary innate immunity. They are collagen-containing C-type (calcium-dependent) lectins, called collectins, and are structurally similar to mannose-binding protein of the lectin pathway of the complement system. Being carbohydrate pattern-recognition molecules, they recognize a broad spectrum of pathogens and allergens via the lectin domain, with subsequent activation of immune cells via the collagen region, thus offering protection against infection and allergenic challenge. SP-A and SP-D have been shown to be involved in viral neutralization, clearance of bacteria, fungi, and apoptotic and necrotic cells, the down-regulation of allergic reaction, and the resolution of inflammation. Studies on single-nucleotide polymorphism, protein levels in broncho-alveolar lavage, and gene knock-out mice have clearly indicated an association between SP-A and SP-D and a range of pulmonary diseases. In addition, recent studies using murine models of allergy and infection have raised the possibility that the recombinant forms of SP-A and SP-D may have therapeutic potential in controlling pulmonary infection, inflammation, and allergies in humans.

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1 Acta Physica Polonica A

1 Archivum Immunologiae et Therapiae Experimentalis

1 2005

1 2004

2 Chakraborty T.

1 Apalkov V.

1 Bichler M.

1 Broocks K.

1 Heitmann D.

1 Heyn C.

1 Kamran M. F.

1 Kishore U.

1 Lopez B. A.

1 Madan T.

1 Sarma P. U.

1 Saxena S.

1 Schröter P.

1 Schüller C.

1 Singh M.

1 Wegscheider W.

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Charged Excitons in the Quantum Hall Regime

Surfactant proteins SP-A and SP-D in human health and dis