ACTA

Charged Excitons in the Quantum Hall Regime

C. Schüller^a, K.-B. Broocks^a, P. Schröter^a, C. Heyn^a, D. Heitmann^a, M. Bichler^b, W. Wegscheider^c, V.M. Apalkov^d and T. Chakraborty^e
^aInstitut für Angewandte Physik und Zentrum für Mikrostrukturforschung,
Universität Hamburg, Jungiusstrasse 11, 20355 Hamburg, Germany
^bWalter-Schottky-Institut der Technischen Universität München,
Am Coulombwall, 85748 Garching, Germany
^cInstitut für Experimentelle und Angewandte Physik, Universität Regensburg,
93040 Regensburg, Germany
^dPhysics Department, University of Utah,
Salt Lake City, Utah 84112-0830, USA
^e Department of Physics and Astronomy, University of Manitoba,
Winnipeg, Manitoba, R3T 2N2, Canada

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Received: 10 06 2004

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 1×10¹⁰ cm^-2 and 2×10¹¹ 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.

DOI: 10.12693/APhysPolA.106.341
PACS numbers: 71.35.-y, 71.30.+h, 71.35.Ji, 71.70.Ej